spring-cloud-sleuth/1.2.x/spring-cloud-sleuth.xml

<?xml version="1.0" encoding="UTF-8"?>
<?asciidoc-toc maxdepth="8"?>
<?asciidoc-numbered?>
<book xmlns="http://docbook.org/ns/docbook" xmlns:xl="http://www.w3.org/1999/xlink" version="5.0" xml:lang="en">
<info>
<title>Spring Cloud Sleuth</title>
<date>2018-07-20</date>
<author>
<personname>
<firstname>Adrian Cole, Spencer Gibb, Marcin Grzejszczak, Dave Syer</firstname>
</personname>
</author>
<authorinitials>A</authorinitials>
</info>
<preface>
<title></title>
<simpara><emphasis role="strong">1.2.7.BUILD-SNAPSHOT</emphasis></simpara>
</preface>
<chapter xml:id="_introduction">
<title>Introduction</title>
<simpara>Spring Cloud Sleuth implements a distributed tracing solution for <link xl:href="https://cloud.spring.io">Spring Cloud</link>.</simpara>
<section xml:id="_terminology">
<title>Terminology</title>
<simpara>Spring Cloud Sleuth borrows <link xl:href="https://research.google.com/pubs/pub36356.html">Dapper&#8217;s</link> terminology.</simpara>
<simpara><emphasis role="strong">Span:</emphasis> The basic unit of work. For example, sending an RPC is a new span, as is sending a response to an
RPC. Span&#8217;s are identified by a unique 64-bit ID for the span and another 64-bit ID for the trace the span
is a part of.  Spans also have other data, such as descriptions, timestamped events, key-value
annotations (tags), the ID of the span that caused them, and process ID&#8217;s (normally IP address).</simpara>
<simpara>Spans are started and stopped, and they keep track of their timing information.  Once you create a
span, you must stop it at some point in the future.</simpara>
<tip>
<simpara>The initial span that starts a trace is called a <literal>root span</literal>. The value of span id
of that span is equal to trace id.</simpara>
</tip>
<simpara><emphasis role="strong">Trace:</emphasis> A set of spans forming a tree-like structure.  For example, if you are running a distributed
big-data store, a trace might be formed by a put request.</simpara>
<simpara><emphasis role="strong">Annotation:</emphasis>  is used to record existence of an event in time. Some of the core annotations used to define
the start and stop of a request are:</simpara>
<itemizedlist>
<listitem>
<simpara><emphasis role="strong">cs</emphasis> - Client Sent - The client has made a request. This annotation depicts the start of the span.</simpara>
</listitem>
<listitem>
<simpara><emphasis role="strong">sr</emphasis> - Server Received -  The server side got the request and will start processing it.
If one subtracts the cs timestamp from this timestamp one will receive the network latency.</simpara>
</listitem>
<listitem>
<simpara><emphasis role="strong">ss</emphasis> - Server Sent -  Annotated upon completion of request processing (when the response
got sent back to the client). If one subtracts the sr timestamp from this timestamp one
will receive the time needed by the server side to process the request.</simpara>
</listitem>
<listitem>
<simpara><emphasis role="strong">cr</emphasis> - Client Received - Signifies the end of the span. The client has successfully received the
response from the server side. If one subtracts the cs timestamp from this timestamp one
will receive the whole time needed by the client to receive the response from the server.</simpara>
</listitem>
</itemizedlist>
<simpara>Visualization of what <emphasis role="strong">Span</emphasis> and <emphasis role="strong">Trace</emphasis> will look in a system together with the Zipkin annotations:</simpara>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="https://raw.githubusercontent.com/spring-cloud/spring-cloud-sleuth/master/docs/src/main/asciidoc/images/trace-id.png"/>
</imageobject>
<textobject><phrase>Trace Info propagation</phrase></textobject>
</mediaobject>
</informalfigure>
<simpara>Each color of a note signifies a span (7 spans - from <emphasis role="strong">A</emphasis> to <emphasis role="strong">G</emphasis>). If you have such information in the note:</simpara>
<screen>Trace Id = X
Span Id = D
Client Sent</screen>
<simpara>That means that the current span has <emphasis role="strong">Trace-Id</emphasis> set to <emphasis role="strong">X</emphasis>, <emphasis role="strong">Span-Id</emphasis> set to <emphasis role="strong">D</emphasis>. It also has emitted
 <emphasis role="strong">Client Sent</emphasis> event.</simpara>
<simpara>This is how the visualization of the parent / child relationship of spans would look like:</simpara>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="https://raw.githubusercontent.com/spring-cloud/spring-cloud-sleuth/master/docs/src/main/asciidoc/images/parents.png"/>
</imageobject>
<textobject><phrase>Parent child relationship</phrase></textobject>
</mediaobject>
</informalfigure>
</section>
<section xml:id="_purpose">
<title>Purpose</title>
<simpara>In the following sections the example from the image above will be taken into consideration.</simpara>
<section xml:id="_distributed_tracing_with_zipkin">
<title>Distributed tracing with Zipkin</title>
<simpara>Altogether there are <emphasis role="strong">7 spans</emphasis> . If you go to traces in Zipkin you will see this number in the second trace:</simpara>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="https://raw.githubusercontent.com/spring-cloud/spring-cloud-sleuth/master/docs/src/main/asciidoc/images/zipkin-traces.png"/>
</imageobject>
<textobject><phrase>Traces</phrase></textobject>
</mediaobject>
</informalfigure>
<simpara>However if you pick a particular trace then you will see <emphasis role="strong">4 spans</emphasis>:</simpara>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="https://raw.githubusercontent.com/spring-cloud/spring-cloud-sleuth/master/docs/src/main/asciidoc/images/zipkin-ui.png"/>
</imageobject>
<textobject><phrase>Traces Info propagation</phrase></textobject>
</mediaobject>
</informalfigure>
<note>
<simpara>When picking a particular trace you will see merged spans. That means that if there were 2 spans sent to
Zipkin with Server Received and Server Sent / Client Received and Client Sent
annotations then they will presented as a single span.</simpara>
</note>
<simpara>Why is there a difference between the 7 and 4 spans in this case?</simpara>
<itemizedlist>
<listitem>
<simpara>2 spans come from <literal>http:/start</literal> span. It has the Server Received (SR) and Server Sent (SS) annotations.</simpara>
</listitem>
<listitem>
<simpara>2 spans come from the RPC call from <literal>service1</literal> to <literal>service2</literal> to the <literal>http:/foo</literal> endpoint. It has the Client Sent (CS)
and Client Received (CR) annotations on <literal>service1</literal> side. It also has Server Received (SR) and Server Sent (SS) annotations
on the <literal>service2</literal> side. Physically there are 2 spans but they form 1 logical span related to an RPC call.</simpara>
</listitem>
<listitem>
<simpara>2 spans come from the RPC call from <literal>service2</literal> to <literal>service3</literal> to the <literal>http:/bar</literal> endpoint. It has the Client Sent (CS)
and Client Received (CR) annotations on <literal>service2</literal> side. It also has Server Received (SR) and Server Sent (SS) annotations
on the <literal>service3</literal> side. Physically there are 2 spans but they form 1 logical span related to an RPC call.</simpara>
</listitem>
<listitem>
<simpara>2 spans come from the RPC call from <literal>service2</literal> to <literal>service4</literal> to the <literal>http:/baz</literal> endpoint. It has the Client Sent (CS)
and Client Received (CR) annotations on <literal>service2</literal> side. It also has Server Received (SR) and Server Sent (SS) annotations
on the <literal>service4</literal> side. Physically there are 2 spans but they form 1 logical span related to an RPC call.</simpara>
</listitem>
</itemizedlist>
<simpara>So if we count the physical spans we have <emphasis role="strong">1</emphasis> from <literal>http:/start</literal>, <emphasis role="strong">2</emphasis> from <literal>service1</literal> calling <literal>service2</literal>, <emphasis role="strong">2</emphasis> form <literal>service2</literal>
calling <literal>service3</literal> and <emphasis role="strong">2</emphasis> from <literal>service2</literal> calling <literal>service4</literal>. Altogether <emphasis role="strong">7</emphasis> spans.</simpara>
<simpara>Logically we see the information of <emphasis role="strong">Total Spans: 4</emphasis> because we have <emphasis role="strong">1</emphasis> span related to the incoming request
to <literal>service1</literal> and <emphasis role="strong">3</emphasis> spans related to RPC calls.</simpara>
</section>
<section xml:id="_visualizing_errors">
<title>Visualizing errors</title>
<simpara>Zipkin allows you to visualize errors in your trace. When an exception was thrown and wasn&#8217;t caught then we&#8217;re
setting proper tags on the span which Zipkin can properly colorize. You could see in the list of traces one
  trace that was in red color. That&#8217;s because there was an exception thrown.</simpara>
<simpara>If you click that trace then you&#8217;ll see a similar picture</simpara>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="https://raw.githubusercontent.com/spring-cloud/spring-cloud-sleuth/master/docs/src/main/asciidoc/images/zipkin-error-traces.png"/>
</imageobject>
<textobject><phrase>Error Traces</phrase></textobject>
</mediaobject>
</informalfigure>
<simpara>Then if you click on one of the spans you&#8217;ll see the following</simpara>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="https://raw.githubusercontent.com/spring-cloud/spring-cloud-sleuth/master/docs/src/main/asciidoc/images/zipkin-error-trace-screenshot.png"/>
</imageobject>
<textobject><phrase>Error Traces Info propagation</phrase></textobject>
</mediaobject>
</informalfigure>
<simpara>As you can see you can easily see the reason for an error and the whole stacktrace related to it.</simpara>
</section>
<section xml:id="_live_examples">
<title>Live examples</title>
<figure>
<title>Click Pivotal Web Services icon to see it live!</title>
<mediaobject>
<imageobject>
<imagedata fileref="https://raw.githubusercontent.com/spring-cloud/spring-cloud-sleuth/master/docs/src/main/asciidoc/images/pws.png" contentwidth="150" contentdepth="74"/>
</imageobject>
<textobject><phrase>Zipkin deployed on Pivotal Web Services</phrase></textobject>
</mediaobject>
</figure>
<simpara>The dependency graph in Zipkin would look like this:</simpara>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="https://raw.githubusercontent.com/spring-cloud/spring-cloud-sleuth/master/docs/src/main/asciidoc/images/dependencies.png"/>
</imageobject>
<textobject><phrase>Dependencies</phrase></textobject>
</mediaobject>
</informalfigure>
<figure>
<title>Click Pivotal Web Services icon to see it live!</title>
<mediaobject>
<imageobject>
<imagedata fileref="https://raw.githubusercontent.com/spring-cloud/spring-cloud-sleuth/master/docs/src/main/asciidoc/images/pws.png" contentwidth="150" contentdepth="74"/>
</imageobject>
<textobject><phrase>Zipkin deployed on Pivotal Web Services</phrase></textobject>
</mediaobject>
</figure>
</section>
<section xml:id="_log_correlation">
<title>Log correlation</title>
<simpara>When grepping the logs of those four applications by trace id equal to e.g. <literal>2485ec27856c56f4</literal> one would get the following:</simpara>
<screen>service1.log:2016-02-26 11:15:47.561  INFO [service1,2485ec27856c56f4,2485ec27856c56f4,true] 68058 --- [nio-8081-exec-1] i.s.c.sleuth.docs.service1.Application   : Hello from service1. Calling service2
service2.log:2016-02-26 11:15:47.710  INFO [service2,2485ec27856c56f4,9aa10ee6fbde75fa,true] 68059 --- [nio-8082-exec-1] i.s.c.sleuth.docs.service2.Application   : Hello from service2. Calling service3 and then service4
service3.log:2016-02-26 11:15:47.895  INFO [service3,2485ec27856c56f4,1210be13194bfe5,true] 68060 --- [nio-8083-exec-1] i.s.c.sleuth.docs.service3.Application   : Hello from service3
service2.log:2016-02-26 11:15:47.924  INFO [service2,2485ec27856c56f4,9aa10ee6fbde75fa,true] 68059 --- [nio-8082-exec-1] i.s.c.sleuth.docs.service2.Application   : Got response from service3 [Hello from service3]
service4.log:2016-02-26 11:15:48.134  INFO [service4,2485ec27856c56f4,1b1845262ffba49d,true] 68061 --- [nio-8084-exec-1] i.s.c.sleuth.docs.service4.Application   : Hello from service4
service2.log:2016-02-26 11:15:48.156  INFO [service2,2485ec27856c56f4,9aa10ee6fbde75fa,true] 68059 --- [nio-8082-exec-1] i.s.c.sleuth.docs.service2.Application   : Got response from service4 [Hello from service4]
service1.log:2016-02-26 11:15:48.182  INFO [service1,2485ec27856c56f4,2485ec27856c56f4,true] 68058 --- [nio-8081-exec-1] i.s.c.sleuth.docs.service1.Application   : Got response from service2 [Hello from service2, response from service3 [Hello from service3] and from service4 [Hello from service4]]</screen>
<simpara>If you&#8217;re using a log aggregating tool like <link xl:href="https://www.elastic.co/products/kibana">Kibana</link>,
<link xl:href="https://www.splunk.com/">Splunk</link> etc. you can order the events that took place. An example of
Kibana would look like this:</simpara>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="https://raw.githubusercontent.com/spring-cloud/spring-cloud-sleuth/master/docs/src/main/asciidoc/images/kibana.png"/>
</imageobject>
<textobject><phrase>Log correlation with Kibana</phrase></textobject>
</mediaobject>
</informalfigure>
<simpara>If you want to use <link xl:href="https://www.elastic.co/guide/en/logstash/current/index.html">Logstash</link> here is the Grok pattern for Logstash:</simpara>
<screen>filter {
       # pattern matching logback pattern
       grok {
              match =&gt; { "message" =&gt; "%{TIMESTAMP_ISO8601:timestamp}\s+%{LOGLEVEL:severity}\s+\[%{DATA:service},%{DATA:trace},%{DATA:span},%{DATA:exportable}\]\s+%{DATA:pid}\s+---\s+\[%{DATA:thread}\]\s+%{DATA:class}\s+:\s+%{GREEDYDATA:rest}" }
       }
}</screen>
<note>
<simpara>If you want to use Grok together with the logs from Cloud Foundry you have to use this pattern:</simpara>
</note>
<screen>filter {
       # pattern matching logback pattern
       grok {
              match =&gt; { "message" =&gt; "(?m)OUT\s+%{TIMESTAMP_ISO8601:timestamp}\s+%{LOGLEVEL:severity}\s+\[%{DATA:service},%{DATA:trace},%{DATA:span},%{DATA:exportable}\]\s+%{DATA:pid}\s+---\s+\[%{DATA:thread}\]\s+%{DATA:class}\s+:\s+%{GREEDYDATA:rest}" }
       }
}</screen>
<section xml:id="_json_logback_with_logstash">
<title>JSON Logback with Logstash</title>
<simpara>Often you do not want to store your logs in a text file but in a JSON file that Logstash can immediately pick. To do that you have to do the following (for readability
we&#8217;re passing the dependencies in the <literal>groupId:artifactId:version</literal> notation.</simpara>
<simpara><emphasis role="strong">Dependencies setup</emphasis></simpara>
<itemizedlist>
<listitem>
<simpara>Ensure that Logback is on the classpath (<literal>ch.qos.logback:logback-core</literal>)</simpara>
</listitem>
<listitem>
<simpara>Add Logstash Logback encode - example for version <literal>4.6</literal> : <literal>net.logstash.logback:logstash-logback-encoder:4.6</literal></simpara>
</listitem>
</itemizedlist>
<simpara><emphasis role="strong">Logback setup</emphasis></simpara>
<simpara>Below you can find an example of a Logback configuration (file named <link xl:href="https://github.com/spring-cloud-samples/sleuth-documentation-apps/blob/master/service1/src/main/resources/logback-spring.xml">logback-spring.xml</link>) that:</simpara>
<itemizedlist>
<listitem>
<simpara>logs information from the application in a JSON format to a <literal>build/${spring.application.name}.json</literal> file</simpara>
</listitem>
<listitem>
<simpara>has commented out two additional appenders - console and standard log file</simpara>
</listitem>
<listitem>
<simpara>has the same logging pattern as the one presented in the previous section</simpara>
</listitem>
</itemizedlist>
<programlisting language="xml" linenumbering="unnumbered">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;configuration&gt;
	&lt;include resource="org/springframework/boot/logging/logback/defaults.xml"/&gt;
	​
	&lt;springProperty scope="context" name="springAppName" source="spring.application.name"/&gt;
	&lt;!-- Example for logging into the build folder of your project --&gt;
	&lt;property name="LOG_FILE" value="${BUILD_FOLDER:-build}/${springAppName}"/&gt;​

	&lt;!-- You can override this to have a custom pattern --&gt;
	&lt;property name="CONSOLE_LOG_PATTERN"
			  value="%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){faint} %clr(${LOG_LEVEL_PATTERN:-%5p}) %clr(${PID:- }){magenta} %clr(---){faint} %clr([%15.15t]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}"/&gt;

	&lt;!-- Appender to log to console --&gt;
	&lt;appender name="console" class="ch.qos.logback.core.ConsoleAppender"&gt;
		&lt;filter class="ch.qos.logback.classic.filter.ThresholdFilter"&gt;
			&lt;!-- Minimum logging level to be presented in the console logs--&gt;
			&lt;level&gt;DEBUG&lt;/level&gt;
		&lt;/filter&gt;
		&lt;encoder&gt;
			&lt;pattern&gt;${CONSOLE_LOG_PATTERN}&lt;/pattern&gt;
			&lt;charset&gt;utf8&lt;/charset&gt;
		&lt;/encoder&gt;
	&lt;/appender&gt;

	&lt;!-- Appender to log to file --&gt;​
	&lt;appender name="flatfile" class="ch.qos.logback.core.rolling.RollingFileAppender"&gt;
		&lt;file&gt;${LOG_FILE}&lt;/file&gt;
		&lt;rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy"&gt;
			&lt;fileNamePattern&gt;${LOG_FILE}.%d{yyyy-MM-dd}.gz&lt;/fileNamePattern&gt;
			&lt;maxHistory&gt;7&lt;/maxHistory&gt;
		&lt;/rollingPolicy&gt;
		&lt;encoder&gt;
			&lt;pattern&gt;${CONSOLE_LOG_PATTERN}&lt;/pattern&gt;
			&lt;charset&gt;utf8&lt;/charset&gt;
		&lt;/encoder&gt;
	&lt;/appender&gt;
	​
	&lt;!-- Appender to log to file in a JSON format --&gt;
	&lt;appender name="logstash" class="ch.qos.logback.core.rolling.RollingFileAppender"&gt;
		&lt;file&gt;${LOG_FILE}.json&lt;/file&gt;
		&lt;rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy"&gt;
			&lt;fileNamePattern&gt;${LOG_FILE}.json.%d{yyyy-MM-dd}.gz&lt;/fileNamePattern&gt;
			&lt;maxHistory&gt;7&lt;/maxHistory&gt;
		&lt;/rollingPolicy&gt;
		&lt;encoder class="net.logstash.logback.encoder.LoggingEventCompositeJsonEncoder"&gt;
			&lt;providers&gt;
				&lt;timestamp&gt;
					&lt;timeZone&gt;UTC&lt;/timeZone&gt;
				&lt;/timestamp&gt;
				&lt;pattern&gt;
					&lt;pattern&gt;
						{
						"severity": "%level",
						"service": "${springAppName:-}",
						"trace": "%X{X-B3-TraceId:-}",
						"span": "%X{X-B3-SpanId:-}",
						"parent": "%X{X-B3-ParentSpanId:-}",
						"exportable": "%X{X-Span-Export:-}",
						"pid": "${PID:-}",
						"thread": "%thread",
						"class": "%logger{40}",
						"rest": "%message"
						}
					&lt;/pattern&gt;
				&lt;/pattern&gt;
			&lt;/providers&gt;
		&lt;/encoder&gt;
	&lt;/appender&gt;
	​
	&lt;root level="INFO"&gt;
		&lt;appender-ref ref="console"/&gt;
		&lt;!-- uncomment this to have also JSON logs --&gt;
		&lt;!--&lt;appender-ref ref="logstash"/&gt;--&gt;
		&lt;!--&lt;appender-ref ref="flatfile"/&gt;--&gt;
	&lt;/root&gt;
&lt;/configuration&gt;</programlisting>
<note>
<simpara>If you&#8217;re using a custom <literal>logback-spring.xml</literal> then you have to pass the <literal>spring.application.name</literal> in
<literal>bootstrap</literal> instead of <literal>application</literal> property file. Otherwise your custom logback file won&#8217;t read the property properly.</simpara>
</note>
</section>
</section>
<section xml:id="_propagating_span_context">
<title>Propagating Span Context</title>
<simpara>The span context is the state that must get propagated to any child Spans across process boundaries.
Part of the Span Context is the Baggage. The trace and span IDs are a required part of the span context.
Baggage is an optional part.</simpara>
<simpara>Baggage is a set of key:value pairs stored in the span context. Baggage travels together with the trace
and is attached to every span. Spring Cloud Sleuth will understand that a header is baggage related if the HTTP
 header is prefixed with <literal>baggage-</literal> and for messaging it starts with <literal>baggage_</literal>.</simpara>
<important>
<simpara>There&#8217;s currently no limitation of the count or size of baggage items. However, keep in mind that
too many can decrease system throughput or increase RPC latency. In extreme cases, it could crash the app due
to exceeding transport-level message or header capacity.</simpara>
</important>
<simpara>Example of setting baggage on a span:</simpara>
<programlisting language="java" linenumbering="unnumbered">Span initialSpan = this.tracer.nextSpan().name("span").start();
try (Tracer.SpanInScope ws = this.tracer.withSpanInScope(initialSpan)) {
	ExtraFieldPropagation.set("foo", "bar");
	ExtraFieldPropagation.set("UPPER_CASE", "someValue");</programlisting>
<section xml:id="_baggage_vs_span_tags">
<title>Baggage vs. Span Tags</title>
<simpara>Baggage travels with the trace (i.e. every child span contains the baggage of its parent). Zipkin has no knowledge of
baggage and will not even receive that information.</simpara>
<simpara>Tags are attached to a specific span - they are presented for that particular span only. However you
can search by tag to find the trace, where there exists a span having the searched tag value.</simpara>
<simpara>If you want to be able to lookup a span based on baggage, you should add corresponding entry as a tag in the root span.</simpara>
<programlisting language="java" linenumbering="unnumbered">@Autowired Tracer tracer;

Span span = tracer.getCurrentSpan();
String baggageKey = "key";
String baggageValue = "foo";
span.setBaggageItem(baggageKey, baggageValue);
tracer.addTag(baggageKey, baggageValue);</programlisting>
</section>
</section>
</section>
<section xml:id="_adding_to_the_project">
<title>Adding to the project</title>
<section xml:id="_only_sleuth_log_correlation">
<title>Only Sleuth (log correlation)</title>
<simpara>If you want to profit only from Spring Cloud Sleuth without the Zipkin integration just add
the <literal>spring-cloud-starter-sleuth</literal> module to your project.</simpara>
<formalpara role="primary">
<title>Maven</title>
<para>
<programlisting language="xml" linenumbering="unnumbered">&lt;dependencyManagement&gt; <co xml:id="CO1-1"/>
         &lt;dependencies&gt;
             &lt;dependency&gt;
                 &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
                 &lt;artifactId&gt;spring-cloud-dependencies&lt;/artifactId&gt;
                 &lt;version&gt;${release.train.version}&lt;/version&gt;
                 &lt;type&gt;pom&lt;/type&gt;
                 &lt;scope&gt;import&lt;/scope&gt;
             &lt;/dependency&gt;
         &lt;/dependencies&gt;
   &lt;/dependencyManagement&gt;

   &lt;dependency&gt; <co xml:id="CO1-2"/>
       &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
       &lt;artifactId&gt;spring-cloud-starter-sleuth&lt;/artifactId&gt;
   &lt;/dependency&gt;</programlisting>
</para>
</formalpara>
<calloutlist>
<callout arearefs="CO1-1">
<para>In order not to pick versions by yourself it&#8217;s much better if you add the dependency management via
the Spring BOM</para>
</callout>
<callout arearefs="CO1-2">
<para>Add the dependency to <literal>spring-cloud-starter-sleuth</literal></para>
</callout>
</calloutlist>
<formalpara role="secondary">
<title>Gradle</title>
<para>
<programlisting language="groovy" linenumbering="unnumbered">dependencyManagement { <co xml:id="CO2-1"/>
    imports {
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:${releaseTrainVersion}"
    }
}

dependencies { <co xml:id="CO2-2"/>
    compile "org.springframework.cloud:spring-cloud-starter-sleuth"
}</programlisting>
</para>
</formalpara>
<calloutlist>
<callout arearefs="CO2-1">
<para>In order not to pick versions by yourself it&#8217;s much better if you add the dependency management via
the Spring BOM</para>
</callout>
<callout arearefs="CO2-2">
<para>Add the dependency to <literal>spring-cloud-starter-sleuth</literal></para>
</callout>
</calloutlist>
</section>
<section xml:id="_sleuth_with_zipkin_via_http">
<title>Sleuth with Zipkin via HTTP</title>
<simpara>If you want both Sleuth and Zipkin just add the <literal>spring-cloud-starter-zipkin</literal> dependency.</simpara>
<formalpara role="primary">
<title>Maven</title>
<para>
<programlisting language="xml" linenumbering="unnumbered">&lt;dependencyManagement&gt; <co xml:id="CO3-1"/>
         &lt;dependencies&gt;
             &lt;dependency&gt;
                 &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
                 &lt;artifactId&gt;spring-cloud-dependencies&lt;/artifactId&gt;
                 &lt;version&gt;${release.train.version}&lt;/version&gt;
                 &lt;type&gt;pom&lt;/type&gt;
                 &lt;scope&gt;import&lt;/scope&gt;
             &lt;/dependency&gt;
         &lt;/dependencies&gt;
   &lt;/dependencyManagement&gt;

   &lt;dependency&gt; <co xml:id="CO3-2"/>
       &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
       &lt;artifactId&gt;spring-cloud-starter-zipkin&lt;/artifactId&gt;
   &lt;/dependency&gt;</programlisting>
</para>
</formalpara>
<calloutlist>
<callout arearefs="CO3-1">
<para>In order not to pick versions by yourself it&#8217;s much better if you add the dependency management via
the Spring BOM</para>
</callout>
<callout arearefs="CO3-2">
<para>Add the dependency to <literal>spring-cloud-starter-zipkin</literal></para>
</callout>
</calloutlist>
<formalpara role="secondary">
<title>Gradle</title>
<para>
<programlisting language="groovy" linenumbering="unnumbered">dependencyManagement { <co xml:id="CO4-1"/>
    imports {
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:${releaseTrainVersion}"
    }
}

dependencies { <co xml:id="CO4-2"/>
    compile "org.springframework.cloud:spring-cloud-starter-zipkin"
}</programlisting>
</para>
</formalpara>
<calloutlist>
<callout arearefs="CO4-1">
<para>In order not to pick versions by yourself it&#8217;s much better if you add the dependency management via
the Spring BOM</para>
</callout>
<callout arearefs="CO4-2">
<para>Add the dependency to <literal>spring-cloud-starter-zipkin</literal></para>
</callout>
</calloutlist>
</section>
<section xml:id="_sleuth_with_zipkin_via_spring_cloud_stream">
<title>Sleuth with Zipkin via Spring Cloud Stream</title>
<simpara>If you want both Sleuth and Zipkin just add the <literal>spring-cloud-sleuth-stream</literal> dependency.</simpara>
<formalpara role="primary">
<title>Maven</title>
<para>
<programlisting language="xml" linenumbering="unnumbered">&lt;dependencyManagement&gt; <co xml:id="CO5-1"/>
         &lt;dependencies&gt;
             &lt;dependency&gt;
                 &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
                 &lt;artifactId&gt;spring-cloud-dependencies&lt;/artifactId&gt;
                 &lt;version&gt;${release.train.version}&lt;/version&gt;
                 &lt;type&gt;pom&lt;/type&gt;
                 &lt;scope&gt;import&lt;/scope&gt;
             &lt;/dependency&gt;
         &lt;/dependencies&gt;
   &lt;/dependencyManagement&gt;

   &lt;dependency&gt; <co xml:id="CO5-2"/>
       &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
       &lt;artifactId&gt;spring-cloud-sleuth-stream&lt;/artifactId&gt;
   &lt;/dependency&gt;
   &lt;dependency&gt; <co xml:id="CO5-3"/>
       &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
       &lt;artifactId&gt;spring-cloud-starter-sleuth&lt;/artifactId&gt;
   &lt;/dependency&gt;
   &lt;!-- EXAMPLE FOR RABBIT BINDING --&gt;
   &lt;dependency&gt; <co xml:id="CO5-4"/>
       &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
       &lt;artifactId&gt;spring-cloud-stream-binder-rabbit&lt;/artifactId&gt;
   &lt;/dependency&gt;</programlisting>
</para>
</formalpara>
<calloutlist>
<callout arearefs="CO5-1">
<para>In order not to pick versions by yourself it&#8217;s much better if you add the dependency management via
the Spring BOM</para>
</callout>
<callout arearefs="CO5-2">
<para>Add the dependency to <literal>spring-cloud-sleuth-stream</literal></para>
</callout>
<callout arearefs="CO5-3">
<para>Add the dependency to <literal>spring-cloud-starter-sleuth</literal> - that way all dependant dependencies will be downloaded</para>
</callout>
<callout arearefs="CO5-4">
<para>Add a binder (e.g. Rabbit binder) to tell Spring Cloud Stream what it should bind to</para>
</callout>
</calloutlist>
<formalpara role="secondary">
<title>Gradle</title>
<para>
<programlisting language="groovy" linenumbering="unnumbered">dependencyManagement { <co xml:id="CO6-1"/>
    imports {
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:${releaseTrainVersion}"
    }
}

dependencies {
    compile "org.springframework.cloud:spring-cloud-sleuth-stream" <co xml:id="CO6-2"/>
    compile "org.springframework.cloud:spring-cloud-starter-sleuth" <co xml:id="CO6-3"/>
    // Example for Rabbit binding
    compile "org.springframework.cloud:spring-cloud-stream-binder-rabbit" <co xml:id="CO6-4"/>
}</programlisting>
</para>
</formalpara>
<calloutlist>
<callout arearefs="CO6-1">
<para>In order not to pick versions by yourself it&#8217;s much better if you add the dependency management via
the Spring BOM</para>
</callout>
<callout arearefs="CO6-2">
<para>Add the dependency to <literal>spring-cloud-sleuth-stream</literal></para>
</callout>
<callout arearefs="CO6-3">
<para>Add the dependency to <literal>spring-cloud-starter-sleuth</literal> - that way all dependant dependencies will be downloaded</para>
</callout>
<callout arearefs="CO6-4">
<para>Add a binder (e.g. Rabbit binder) to tell Spring Cloud Stream what it should bind to</para>
</callout>
</calloutlist>
</section>
<section xml:id="_spring_cloud_sleuth_stream_zipkin_collector">
<title>Spring Cloud Sleuth Stream Zipkin Collector</title>
<simpara>If you want to start a Spring Cloud Sleuth Stream Zipkin collector just add the <literal>spring-cloud-sleuth-zipkin-stream</literal>
dependency</simpara>
<formalpara role="primary">
<title>Maven</title>
<para>
<programlisting language="xml" linenumbering="unnumbered">&lt;dependencyManagement&gt; <co xml:id="CO7-1"/>
         &lt;dependencies&gt;
             &lt;dependency&gt;
                 &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
                 &lt;artifactId&gt;spring-cloud-dependencies&lt;/artifactId&gt;
                 &lt;version&gt;${release.train.version}&lt;/version&gt;
                 &lt;type&gt;pom&lt;/type&gt;
                 &lt;scope&gt;import&lt;/scope&gt;
             &lt;/dependency&gt;
         &lt;/dependencies&gt;
   &lt;/dependencyManagement&gt;

   &lt;dependency&gt; <co xml:id="CO7-2"/>
       &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
       &lt;artifactId&gt;spring-cloud-sleuth-zipkin-stream&lt;/artifactId&gt;
   &lt;/dependency&gt;
   &lt;dependency&gt; <co xml:id="CO7-3"/>
       &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
       &lt;artifactId&gt;spring-cloud-starter-sleuth&lt;/artifactId&gt;
   &lt;/dependency&gt;
   &lt;!-- EXAMPLE FOR RABBIT BINDING --&gt;
   &lt;dependency&gt; <co xml:id="CO7-4"/>
       &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
       &lt;artifactId&gt;spring-cloud-stream-binder-rabbit&lt;/artifactId&gt;
   &lt;/dependency&gt;</programlisting>
</para>
</formalpara>
<calloutlist>
<callout arearefs="CO7-1">
<para>In order not to pick versions by yourself it&#8217;s much better if you add the dependency management via
the Spring BOM</para>
</callout>
<callout arearefs="CO7-2">
<para>Add the dependency to <literal>spring-cloud-sleuth-zipkin-stream</literal></para>
</callout>
<callout arearefs="CO7-3">
<para>Add the dependency to <literal>spring-cloud-starter-sleuth</literal> - that way all dependant dependencies will be downloaded</para>
</callout>
<callout arearefs="CO7-4">
<para>Add a binder (e.g. Rabbit binder) to tell Spring Cloud Stream what it should bind to</para>
</callout>
</calloutlist>
<formalpara role="secondary">
<title>Gradle</title>
<para>
<programlisting language="groovy" linenumbering="unnumbered">dependencyManagement { <co xml:id="CO8-1"/>
    imports {
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:${releaseTrainVersion}"
    }
}

dependencies {
    compile "org.springframework.cloud:spring-cloud-sleuth-zipkin-stream" <co xml:id="CO8-2"/>
    compile "org.springframework.cloud:spring-cloud-starter-sleuth" <co xml:id="CO8-3"/>
    // Example for Rabbit binding
    compile "org.springframework.cloud:spring-cloud-stream-binder-rabbit" <co xml:id="CO8-4"/>
}</programlisting>
</para>
</formalpara>
<calloutlist>
<callout arearefs="CO8-1">
<para>In order not to pick versions by yourself it&#8217;s much better if you add the dependency management via
the Spring BOM</para>
</callout>
<callout arearefs="CO8-2">
<para>Add the dependency to <literal>spring-cloud-sleuth-zipkin-stream</literal></para>
</callout>
<callout arearefs="CO8-3">
<para>Add the dependency to <literal>spring-cloud-starter-sleuth</literal> - that way all dependant dependencies will be downloaded</para>
</callout>
<callout arearefs="CO8-4">
<para>Add a binder (e.g. Rabbit binder) to tell Spring Cloud Stream what it should bind to</para>
</callout>
</calloutlist>
<simpara>and then just annotate your main class with <literal>@EnableZipkinStreamServer</literal> annotation:</simpara>
<programlisting language="java" linenumbering="unnumbered">package example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.sleuth.zipkin.stream.EnableZipkinStreamServer;

@SpringBootApplication
@EnableZipkinStreamServer
public class ZipkinStreamServerApplication {

	public static void main(String[] args) throws Exception {
		SpringApplication.run(ZipkinStreamServerApplication.class, args);
	}

}</programlisting>
</section>
</section>
</chapter>
<chapter xml:id="_additional_resources">
<title>Additional resources</title>
<simpara><emphasis role="strong">Marcin Grzejszczak talking about Spring Cloud Sleuth and Zipkin</emphasis></simpara>

<simpara><link xl:href="https://www.youtube.com/watch?v=eQV71Mw1u1c">click here to see the video</link></simpara>
</chapter>
<chapter xml:id="_features">
<title>Features</title>
<itemizedlist>
<listitem>
<simpara>Adds trace and span ids to the Slf4J MDC, so you can extract all the logs from a given trace or span in a log aggregator. Example logs:</simpara>
<screen>2016-02-02 15:30:57.902  INFO [bar,6bfd228dc00d216b,6bfd228dc00d216b,false] 23030 --- [nio-8081-exec-3] ...
2016-02-02 15:30:58.372 ERROR [bar,6bfd228dc00d216b,6bfd228dc00d216b,false] 23030 --- [nio-8081-exec-3] ...
2016-02-02 15:31:01.936  INFO [bar,46ab0d418373cbc9,46ab0d418373cbc9,false] 23030 --- [nio-8081-exec-4] ...</screen>
<simpara>notice the <literal>[appname,traceId,spanId,exportable]</literal> entries from the MDC:</simpara>
<itemizedlist>
<listitem>
<simpara><emphasis role="strong">spanId</emphasis> - the id of a specific operation that took place</simpara>
</listitem>
<listitem>
<simpara><emphasis role="strong">appname</emphasis> - the name of the application that logged the span</simpara>
</listitem>
<listitem>
<simpara><emphasis role="strong">traceId</emphasis> - the id of the latency graph that contains the span</simpara>
</listitem>
<listitem>
<simpara><emphasis role="strong">exportable</emphasis> - whether the log should be exported to Zipkin or not. When would you like the span not to be
exportable? In the case in which you want to wrap some operation in a Span and have it written to the logs
only.</simpara>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<simpara>Provides an abstraction over common distributed tracing data models: traces, spans (forming a DAG), annotations,
key-value annotations. Loosely based on HTrace, but Zipkin (Dapper) compatible.</simpara>
</listitem>
<listitem>
<simpara>Sleuth records timing information to aid in latency analysis. Using sleuth, you can pinpoint causes of
latency in your applications. Sleuth is written to not log too much, and to not cause your production application to crash.</simpara>
<itemizedlist>
<listitem>
<simpara>propagates structural data about your call-graph in-band, and the rest out-of-band.</simpara>
</listitem>
<listitem>
<simpara>includes opinionated instrumentation of layers such as HTTP</simpara>
</listitem>
<listitem>
<simpara>includes sampling policy to manage volume</simpara>
</listitem>
<listitem>
<simpara>can report to a Zipkin system for query and visualization</simpara>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<simpara>Instruments common ingress and egress points from Spring applications (servlet filter, async endpoints,
rest template, scheduled actions, message channels, zuul filters, feign client).</simpara>
</listitem>
<listitem>
<simpara>Sleuth includes default logic to join a trace across http or messaging boundaries. For example, http propagation
works via Zipkin-compatible request headers. This propagation logic is defined and customized via
<literal>SpanInjector</literal> and <literal>SpanExtractor</literal> implementations.</simpara>
</listitem>
<listitem>
<simpara>Sleuth gives you the possibility to propagate context (also known as baggage) between processes. That means that if you set on a Span
a baggage element then it will be sent downstream either via HTTP or messaging to other processes.</simpara>
</listitem>
<listitem>
<simpara>Provides a way to create / continue spans and add tags and logs via annotations.</simpara>
</listitem>
<listitem>
<simpara>Provides simple metrics of accepted / dropped spans.</simpara>
</listitem>
<listitem>
<simpara>If <literal>spring-cloud-sleuth-zipkin</literal> then the app will generate and collect Zipkin-compatible traces.
By default it sends them via HTTP to a Zipkin server on localhost (port 9411).
Configure the location of the service using <literal>spring.zipkin.baseUrl</literal>.</simpara>
</listitem>
<listitem>
<simpara>If <literal>spring-cloud-sleuth-stream</literal> then the app will generate and collect traces via <link xl:href="https://github.com/spring-cloud/spring-cloud-stream">Spring Cloud Stream</link>.
Your app automatically becomes a producer of tracer messages that are sent over your broker of choice
(e.g. RabbitMQ, Apache Kafka, Redis).</simpara>
</listitem>
</itemizedlist>
<important>
<simpara>If using Zipkin or Stream, configure the percentage of spans exported using <literal>spring.sleuth.sampler.percentage</literal>
(default 0.1, i.e. 10%). <emphasis role="strong">Otherwise you might think that Sleuth is not working cause it&#8217;s omitting some spans.</emphasis></simpara>
</important>
<note>
<simpara>the SLF4J MDC is always set and logback users will immediately see the trace and span ids in logs per the example
 above. Other logging systems have to configure their own formatter to get the same result. The default is
 <literal>logging.pattern.level</literal> set to <literal>%5p [${spring.zipkin.service.name:${spring.application.name:-}},%X{X-B3-TraceId:-},%X{X-B3-SpanId:-},%X{X-Span-Export:-}]</literal>
 (this is a Spring Boot feature for logback users).
 <emphasis role="strong">This means that if you&#8217;re not using SLF4J this pattern WILL NOT be automatically applied</emphasis>.</simpara>
</note>
</chapter>
<chapter xml:id="_sampling">
<title>Sampling</title>
<simpara>In distributed tracing the data volumes can be very high so sampling
can be important (you usually don&#8217;t need to export all spans to get a
good picture of what is happening). Spring Cloud Sleuth has a
<literal>Sampler</literal> strategy that you can implement to take control of the
sampling algorithm. Samplers do not stop span (correlation) ids from
being generated, but they do prevent the tags and events being
attached and exported. By default you get a strategy that continues to
trace if a span is already active, but new ones are always marked as
non-exportable. If all your apps run with this sampler you will see
traces in logs, but not in any remote store. For testing the default
is often enough, and it probably is all you need if you are only using
the logs (e.g. with an ELK aggregator). If you are exporting span data
to Zipkin or Spring Cloud Stream, there is also an <literal>AlwaysSampler</literal>
that exports everything and a <literal>PercentageBasedSampler</literal> that samples a
fixed fraction of spans.</simpara>
<note>
<simpara>the <literal>PercentageBasedSampler</literal> is the default if you are using
<literal>spring-cloud-sleuth-zipkin</literal> or <literal>spring-cloud-sleuth-stream</literal>. You can
configure the exports using <literal>spring.sleuth.sampler.percentage</literal>. The passed
value needs to be a double from <literal>0.0</literal> to <literal>1.0</literal> so it&#8217;s not a percentage.
For backwards compatibility reasons we&#8217;re not changing the property name.</simpara>
</note>
<simpara>A sampler can be installed just by creating a bean definition, e.g:</simpara>
<programlisting language="java" linenumbering="unnumbered">@Bean
public Sampler defaultSampler() {
	return new AlwaysSampler();
}</programlisting>
<tip>
<simpara>You can set the HTTP header <literal>X-B3-Flags</literal> to <literal>1</literal> or when doing messaging you can
set <literal>spanFlags</literal> header to <literal>1</literal>. Then the current span will be forced to be exportable
regardless of the sampling decision.</simpara>
</tip>
</chapter>
<chapter xml:id="_instrumentation">
<title>Instrumentation</title>
<simpara>Spring Cloud Sleuth instruments all your Spring application
automatically, so you shouldn&#8217;t have to do anything to activate
it. The instrumentation is added using a variety of technologies
according to the stack that is available, e.g. for a servlet web
application we use a <literal>Filter</literal>, and for Spring Integration we use
<literal>ChannelInterceptors</literal>.</simpara>
<simpara>You can customize the keys used in span tags. To limit the volume of
span data, by default an HTTP request will be tagged only with a
handful of metadata like the status code, host and URL. You can add
request headers by configuring <literal>spring.sleuth.keys.http.headers</literal> (a
list of header names).</simpara>
<note>
<simpara>Remember that tags are only collected and exported if there is a
<literal>Sampler</literal> that allows it (by default there is not, so there is no
danger of accidentally collecting too much data without configuring
something).</simpara>
</note>
<note>
<simpara>Currently the instrumentation in Spring Cloud Sleuth is eager - it means that
we&#8217;re actively trying to pass the tracing context between threads. Also timing events
are captured even when sleuth isn&#8217;t exporting data to a tracing system.
This approach may change in the future towards being lazy on this matter.</simpara>
</note>
</chapter>
<chapter xml:id="_span_lifecycle">
<title>Span lifecycle</title>
<simpara>You can do the following operations on the Span by means of <emphasis role="strong">org.springframework.cloud.sleuth.Tracer</emphasis> interface:</simpara>
<itemizedlist>
<listitem>
<simpara><link linkend="creating-and-closing-spans">start</link> - when you start a span its name is assigned and start timestamp is recorded.</simpara>
</listitem>
<listitem>
<simpara><link linkend="creating-and-closing-spans">close</link> - the span gets finished (the end time of the span is recorded) and if
the span is <emphasis role="strong">exportable</emphasis> then it will be eligible for collection to Zipkin.
The span is also removed from the current thread.</simpara>
</listitem>
<listitem>
<simpara><link linkend="continuing-spans">continue</link> - a new instance of span will be created whereas it will be a copy of the
one that it continues.</simpara>
</listitem>
<listitem>
<simpara><link linkend="continuing-spans">detach</link> - the span doesn&#8217;t get stopped or closed. It only gets removed from the current thread.</simpara>
</listitem>
<listitem>
<simpara><link linkend="creating-spans-with-explicit-parent">create with explicit parent</link> - you can create a new span and set an explicit parent to it</simpara>
</listitem>
</itemizedlist>
<tip>
<simpara>Spring creates the instance of <literal>Tracer</literal> for you. In order to use it all you need is to just autowire it.</simpara>
</tip>
<section xml:id="creating-and-closing-spans">
<title>Creating and closing spans</title>
<simpara>You can manually create spans by using the <emphasis role="strong">Tracer</emphasis> interface.</simpara>
<programlisting language="java" linenumbering="unnumbered">// Start a span. If there was a span present in this thread it will become
// the `newSpan`'s parent.
Span newSpan = this.tracer.createSpan("calculateTax");
try {
	// ...
	// You can tag a span
	this.tracer.addTag("taxValue", taxValue);
	// ...
	// You can log an event on a span
	newSpan.logEvent("taxCalculated");
} finally {
	// Once done remember to close the span. This will allow collecting
	// the span to send it to Zipkin
	this.tracer.close(newSpan);
}</programlisting>
<simpara>In this example we could see how to create a new instance of span. Assuming that there already
was a span present in this thread then it would become the parent of that span.</simpara>
<important>
<simpara>Always clean after you create a span! Don&#8217;t forget to close a span if you want to send it to Zipkin.</simpara>
</important>
<important>
<simpara>If your span contains a name greater than 50 chars, then that name will
be truncated to 50 chars. Your names have to be explicit and concrete. Big names lead to
latency issues and sometimes even thrown exceptions.</simpara>
</important>
</section>
<section xml:id="continuing-spans">
<title>Continuing spans</title>
<simpara>Sometimes you don&#8217;t want to create a new span but you want to continue one. Example of such a
situation might be (of course it all depends on the use-case):</simpara>
<itemizedlist>
<listitem>
<simpara><emphasis role="strong">AOP</emphasis> - If there was already a span created before an aspect was reached then you might not want to create a new span.</simpara>
</listitem>
<listitem>
<simpara><emphasis role="strong">Hystrix</emphasis> - executing a Hystrix command is most likely a logical part of the current processing. It&#8217;s in fact
only a technical implementation detail that you wouldn&#8217;t necessarily want to reflect in tracing as a separate being.</simpara>
</listitem>
</itemizedlist>
<simpara>The continued instance of span is equal to the one that it continues:</simpara>
<programlisting language="java" linenumbering="unnumbered">Span continuedSpan = this.tracer.continueSpan(spanToContinue);
assertThat(continuedSpan).isEqualTo(spanToContinue);</programlisting>
<simpara>To continue a span you can use the <emphasis role="strong">Tracer</emphasis> interface.</simpara>
<programlisting language="java" linenumbering="unnumbered">// let's assume that we're in a thread Y and we've received
// the `initialSpan` from thread X
Span continuedSpan = this.tracer.continueSpan(initialSpan);
try {
	// ...
	// You can tag a span
	this.tracer.addTag("taxValue", taxValue);
	// ...
	// You can log an event on a span
	continuedSpan.logEvent("taxCalculated");
} finally {
	// Once done remember to detach the span. That way you'll
	// safely remove it from the current thread without closing it
	this.tracer.detach(continuedSpan);
}</programlisting>
<important>
<simpara>Always clean after you create a span! Don&#8217;t forget to detach a span if some work was done started in one
 thread (e.g. thread X) and it&#8217;s waiting for other threads (e.g. Y, Z) to finish.
 Then the spans in the threads Y, Z should be detached at the end of their work. When the results are collected
 the span in thread X should be closed.</simpara>
</important>
</section>
<section xml:id="creating-spans-with-explicit-parent">
<title>Creating spans with an explicit parent</title>
<simpara>There is a possibility that you want to start a new span and provide an explicit parent of that span.
Let&#8217;s assume that the parent of a span is in one thread and you want to start a new span in another thread. The
<literal>startSpan</literal> method of the <literal>Tracer</literal> interface is the method you are looking for.</simpara>
<programlisting language="java" linenumbering="unnumbered">// let's assume that we're in a thread Y and we've received
// the `initialSpan` from thread X. `initialSpan` will be the parent
// of the `newSpan`
Span newSpan = this.tracer.createSpan("calculateCommission", initialSpan);
try {
	// ...
	// You can tag a span
	this.tracer.addTag("commissionValue", commissionValue);
	// ...
	// You can log an event on a span
	newSpan.logEvent("commissionCalculated");
} finally {
	// Once done remember to close the span. This will allow collecting
	// the span to send it to Zipkin. The tags and events set on the
	// newSpan will not be present on the parent
	this.tracer.close(newSpan);
}</programlisting>
<important>
<simpara>After having created such a span remember to close it. Otherwise you will see a lot of warnings in your logs
 related to the fact that you have a span present in the current thread other than the one you&#8217;re trying to close.
 What&#8217;s worse your spans won&#8217;t get closed properly thus will not get collected to Zipkin.</simpara>
</important>
</section>
</chapter>
<chapter xml:id="_naming_spans">
<title>Naming spans</title>
<simpara>Picking a span name is not a trivial task. Span name should depict an operation name. The name should
be low cardinality (e.g. not include identifiers).</simpara>
<simpara>Since there is a lot of instrumentation going on some of the span names will be
artificial like:</simpara>
<itemizedlist>
<listitem>
<simpara><literal>controller-method-name</literal> when received by a Controller with a method name <literal>conrollerMethodName</literal></simpara>
</listitem>
<listitem>
<simpara><literal>async</literal> for asynchronous operations done via wrapped <literal>Callable</literal> and <literal>Runnable</literal>.</simpara>
</listitem>
<listitem>
<simpara><literal>@Scheduled</literal> annotated methods will return the simple name of the class.</simpara>
</listitem>
</itemizedlist>
<simpara>Fortunately, for the asynchronous processing you can provide explicit naming.</simpara>
<section xml:id="__spanname_annotation">
<title>@SpanName annotation</title>
<simpara>You can name the span explicitly via the <literal>@SpanName</literal> annotation.</simpara>
<programlisting language="java" linenumbering="unnumbered">@SpanName("calculateTax")
class TaxCountingRunnable implements Runnable {

	@Override public void run() {
		// perform logic
	}
}</programlisting>
<simpara>In this case, when processed in the following manner:</simpara>
<programlisting language="java" linenumbering="unnumbered">Runnable runnable = new TraceRunnable(tracer, spanNamer, new TaxCountingRunnable());
Future&lt;?&gt; future = executorService.submit(runnable);
// ... some additional logic ...
future.get();</programlisting>
<simpara>The span will be named <literal>calculateTax</literal>.</simpara>
</section>
<section xml:id="_tostring_method">
<title>toString() method</title>
<simpara>It&#8217;s pretty rare to create separate classes for <literal>Runnable</literal> or <literal>Callable</literal>. Typically one creates an anonymous
instance of those classes. You can&#8217;t annotate such classes thus to override that, if there is no <literal>@SpanName</literal> annotation present,
we&#8217;re checking if the class has a custom implementation of the <literal>toString()</literal> method.</simpara>
<simpara>So executing such code:</simpara>
<programlisting language="java" linenumbering="unnumbered">Runnable runnable = new TraceRunnable(tracer, spanNamer, new Runnable() {
	@Override public void run() {
		// perform logic
	}

	@Override public String toString() {
		return "calculateTax";
	}
});
Future&lt;?&gt; future = executorService.submit(runnable);
// ... some additional logic ...
future.get();</programlisting>
<simpara>will lead in creating a span named <literal>calculateTax</literal>.</simpara>
</section>
</chapter>
<chapter xml:id="_managing_spans_with_annotations">
<title>Managing spans with annotations</title>
<section xml:id="_rationale">
<title>Rationale</title>
<simpara>The main arguments for this features are</simpara>
<itemizedlist>
<listitem>
<simpara>api-agnostic means to collaborate with a span</simpara>
<itemizedlist>
<listitem>
<simpara>use of annotations allows users to add to a span with no library dependency on a span api.
This allows Sleuth to change its core api less impact to user code.</simpara>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<simpara>reduced surface area for basic span operations.</simpara>
<itemizedlist>
<listitem>
<simpara>without this feature one has to use the span api, which has lifecycle commands that
could be used incorrectly. By only exposing scope, tag and log functionality, users can
collaborate without accidentally breaking span lifecycle.</simpara>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<simpara>collaboration with runtime generated code</simpara>
<itemizedlist>
<listitem>
<simpara>with libraries such as Spring Data / Feign the implementations of interfaces are generated
at runtime thus span wrapping of objects was tedious. Now you can provide annotations
 over interfaces and arguments of those interfaces</simpara>
</listitem>
</itemizedlist>
</listitem>
</itemizedlist>
</section>
<section xml:id="_creating_new_spans">
<title>Creating new spans</title>
<simpara>If you really don&#8217;t want to take care of creating local spans manually you can profit from the
<literal>@NewSpan</literal> annotation. Also we give you the <literal>@SpanTag</literal> annotation to add tags in an automated
fashion.</simpara>
<simpara>Let&#8217;s look at some examples of usage.</simpara>
<programlisting language="java" linenumbering="unnumbered">@NewSpan
void testMethod();</programlisting>
<simpara>Annotating the method without any parameter will lead to a creation of a new span whose name
will be equal to annotated method name.</simpara>
<programlisting language="java" linenumbering="unnumbered">@NewSpan("customNameOnTestMethod4")
void testMethod4();</programlisting>
<simpara>If you provide the value in the annotation (either directly or via the <literal>name</literal> parameter) then
the created span will have the name as the provided value.</simpara>
<programlisting language="java" linenumbering="unnumbered">// method declaration
@NewSpan(name = "customNameOnTestMethod5")
void testMethod5(@SpanTag("testTag") String param);

// and method execution
this.testBean.testMethod5("test");</programlisting>
<simpara>You can combine both the name and a tag. Let&#8217;s focus on the latter. In this case whatever the value of
the annotated method&#8217;s parameter runtime value will be - that will be the value of the tag. In our sample
the tag key will be <literal>testTag</literal> and the tag value will be <literal>test</literal>.</simpara>
<programlisting language="java" linenumbering="unnumbered">@NewSpan(name = "customNameOnTestMethod3")
@Override
public void testMethod3() {
}</programlisting>
<simpara>You can place the <literal>@NewSpan</literal> annotation on both the class and an interface. If you override the
interface&#8217;s method and provide a different value of the <literal>@NewSpan</literal> annotation then the most
concrete one wins (in this case <literal>customNameOnTestMethod3</literal> will be set).</simpara>
</section>
<section xml:id="_continuing_spans">
<title>Continuing spans</title>
<simpara>If you want to just add tags and annotations to an existing span it&#8217;s enough
to use the <literal>@ContinueSpan</literal> annotation as presented below. Note that in contrast
with the <literal>@NewSpan</literal> annotation you can also add logs via the <literal>log</literal> parameter:</simpara>
<programlisting language="java" linenumbering="unnumbered">// method declaration
@ContinueSpan(log = "testMethod11")
void testMethod11(@SpanTag("testTag11") String param);

// method execution
this.testBean.testMethod11("test");</programlisting>
<simpara>That way the span will get continued and:</simpara>
<itemizedlist>
<listitem>
<simpara>logs with name <literal>testMethod11.before</literal> and <literal>testMethod11.after</literal> will be created</simpara>
</listitem>
<listitem>
<simpara>if an exception will be thrown a log <literal>testMethod11.afterFailure</literal> will also be created</simpara>
</listitem>
<listitem>
<simpara>tag with key <literal>testTag11</literal> and value <literal>test</literal> will be created</simpara>
</listitem>
</itemizedlist>
</section>
<section xml:id="_more_advanced_tag_setting">
<title>More advanced tag setting</title>
<simpara>There are 3 different ways to add tags to a span. All of them are controlled by the <literal>SpanTag</literal> annotation.
Precedence is:</simpara>
<itemizedlist>
<listitem>
<simpara>try with the bean of <literal>TagValueResolver</literal> type and provided name</simpara>
</listitem>
<listitem>
<simpara>if one hasn&#8217;t provided the bean name, try to evaluate an expression. We&#8217;re searching for a <literal>TagValueExpressionResolver</literal> bean.
The default implementation uses SPEL expression resolution.</simpara>
</listitem>
<listitem>
<simpara>if one hasn&#8217;t provided any expression to evaluate just return a <literal>toString()</literal> value of the parameter</simpara>
</listitem>
</itemizedlist>
<section xml:id="_custom_extractor">
<title>Custom extractor</title>
<simpara>The value of the tag for following method will be computed by an implementation of <literal>TagValueResolver</literal> interface.
Its class name has to be passed as the value of the <literal>resolver</literal> attribute.</simpara>
<simpara>Having such an annotated method:</simpara>
<programlisting language="java" linenumbering="unnumbered">@NewSpan
public void getAnnotationForTagValueResolver(@SpanTag(key = "test", resolver = TagValueResolver.class) String test) {
}</programlisting>
<simpara>and such a <literal>TagValueResolver</literal> bean implementation</simpara>
<programlisting language="java" linenumbering="unnumbered">@Bean(name = "myCustomTagValueResolver")
public TagValueResolver tagValueResolver() {
	return parameter -&gt; "Value from myCustomTagValueResolver";
}</programlisting>
<simpara>Will lead to setting of a tag value equal to <literal>Value from myCustomTagValueResolver</literal>.</simpara>
</section>
<section xml:id="_resolving_expressions_for_value">
<title>Resolving expressions for value</title>
<simpara>Having such an annotated method:</simpara>
<programlisting language="java" linenumbering="unnumbered">@NewSpan
public void getAnnotationForTagValueExpression(@SpanTag(key = "test", expression = "length() + ' characters'") String test) {
}</programlisting>
<simpara>and no custom implementation of a <literal>TagValueExpressionResolver</literal> will lead to evaluation of the SPEL expression and a tag with value <literal>4 characters</literal> will be set on the span.
If you want to use some other expression resolution mechanism you can create your own implementation
of the bean.</simpara>
</section>
<section xml:id="_using_tostring_method">
<title>Using toString method</title>
<simpara>Having such an annotated method:</simpara>
<programlisting language="java" linenumbering="unnumbered">@NewSpan
public void getAnnotationForArgumentToString(@SpanTag("test") Long param) {
}</programlisting>
<simpara>if executed with a value of <literal>15</literal> will lead to setting of a tag with a String value of <literal>"15"</literal>.</simpara>
</section>
</section>
</chapter>
<chapter xml:id="_customizations">
<title>Customizations</title>
<simpara>Thanks to the <literal>SpanInjector</literal> and <literal>SpanExtractor</literal> you can customize the way spans
are created and propagated.</simpara>
<simpara>There are currently two built-in ways to pass tracing information between processes:</simpara>
<itemizedlist>
<listitem>
<simpara>via Spring Integration</simpara>
</listitem>
<listitem>
<simpara>via HTTP</simpara>
</listitem>
</itemizedlist>
<simpara>Span ids are extracted from Zipkin-compatible (B3) headers (either <literal>Message</literal>
or HTTP headers), to start or join an existing trace. Trace information is
injected into any outbound requests so the next hop can extract them.</simpara>
<simpara>The key change in comparison to the previous versions of Sleuth is that Sleuth is implementing
the Open Tracing&#8217;s <literal>TextMap</literal> notion. In Sleuth it&#8217;s called <literal>SpanTextMap</literal>. Basically the idea
is that any means of communication (e.g. message, http request, etc.) can be abstracted via
a <literal>SpanTextMap</literal>. This abstraction defines how one can insert data into the carrier and
how to retrieve it from there. Thanks to this if you want to instrument a new HTTP library
that uses a <literal>FooRequest</literal> as a mean of sending HTTP requests then you have to create an
implementation of  a <literal>SpanTextMap</literal> that delegates calls to <literal>FooRequest</literal> in terms of retrieval
and insertion of HTTP headers.</simpara>
<section xml:id="_spring_integration">
<title>Spring Integration</title>
<simpara>For Spring Integration there are 2 interfaces responsible for creation of a Span from a <literal>Message</literal>.
These are:</simpara>
<itemizedlist>
<listitem>
<simpara><literal>MessagingSpanTextMapExtractor</literal></simpara>
</listitem>
<listitem>
<simpara><literal>MessagingSpanTextMapInjector</literal></simpara>
</listitem>
</itemizedlist>
<simpara>You can override them by providing your own implementation.</simpara>
</section>
<section xml:id="_http">
<title>HTTP</title>
<simpara>For HTTP there are 2 interfaces responsible for creation of a Span from a <literal>Message</literal>.
These are:</simpara>
<itemizedlist>
<listitem>
<simpara><literal>HttpSpanExtractor</literal></simpara>
</listitem>
<listitem>
<simpara><literal>HttpSpanInjector</literal></simpara>
</listitem>
</itemizedlist>
<simpara>You can override them by providing your own implementation.</simpara>
</section>
<section xml:id="_example">
<title>Example</title>
<simpara>Let&#8217;s assume that instead of the standard Zipkin compatible tracing HTTP header names
you have</simpara>
<itemizedlist>
<listitem>
<simpara>for trace id - <literal>correlationId</literal></simpara>
</listitem>
<listitem>
<simpara>for span id - <literal>mySpanId</literal></simpara>
</listitem>
</itemizedlist>
<simpara>This is a an example of a <literal>SpanExtractor</literal></simpara>
<programlisting language="java" linenumbering="unnumbered">static class CustomHttpSpanExtractor implements HttpSpanExtractor {

	@Override public Span joinTrace(SpanTextMap carrier) {
		Map&lt;String, String&gt; map = TextMapUtil.asMap(carrier);
		long traceId = Span.hexToId(map.get("correlationid"));
		long spanId = Span.hexToId(map.get("myspanid"));
		// extract all necessary headers
		Span.SpanBuilder builder = Span.builder().traceId(traceId).spanId(spanId);
		// build rest of the Span
		return builder.build();
	}
}

static class CustomHttpSpanInjector implements HttpSpanInjector {

	@Override
	public void inject(Span span, SpanTextMap carrier) {
		carrier.put("correlationId", span.traceIdString());
		carrier.put("mySpanId", Span.idToHex(span.getSpanId()));
	}
}</programlisting>
<simpara>And you could register it like this:</simpara>
<programlisting language="java" linenumbering="unnumbered">@Bean
HttpSpanInjector customHttpSpanInjector() {
	return new CustomHttpSpanInjector();
}

@Bean
HttpSpanExtractor customHttpSpanExtractor() {
	return new CustomHttpSpanExtractor();
}</programlisting>
<simpara>Spring Cloud Sleuth does not add trace/span related headers to the Http Response for security reasons. If you need the headers then a custom <literal>SpanInjector</literal>
that injects the headers into the Http Response and a Servlet filter which makes use of this can be added the following way:</simpara>
<programlisting language="java" linenumbering="unnumbered">static class CustomHttpServletResponseSpanInjector extends ZipkinHttpSpanInjector {

	@Override
	public void inject(Span span, SpanTextMap carrier) {
		super.inject(span, carrier);
		carrier.put(Span.TRACE_ID_NAME, span.traceIdString());
		carrier.put(Span.SPAN_ID_NAME, Span.idToHex(span.getSpanId()));
	}
}

static class HttpResponseInjectingTraceFilter extends GenericFilterBean {

	private final Tracer tracer;
	private final HttpSpanInjector spanInjector;

	public HttpResponseInjectingTraceFilter(Tracer tracer, HttpSpanInjector spanInjector) {
		this.tracer = tracer;
		this.spanInjector = spanInjector;
	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
		HttpServletResponse response = (HttpServletResponse) servletResponse;
		Span currentSpan = this.tracer.getCurrentSpan();
		this.spanInjector.inject(currentSpan, new HttpServletResponseTextMap(response));
		filterChain.doFilter(request, response);
	}

	 class HttpServletResponseTextMap implements SpanTextMap {

		 private final HttpServletResponse delegate;

		 HttpServletResponseTextMap(HttpServletResponse delegate) {
			 this.delegate = delegate;
		 }

		 @Override
		 public Iterator&lt;Map.Entry&lt;String, String&gt;&gt; iterator() {
			 Map&lt;String, String&gt; map = new HashMap&lt;&gt;();
			 for (String header : this.delegate.getHeaderNames()) {
				map.put(header, this.delegate.getHeader(header));
			 }
			 return map.entrySet().iterator();
		 }

		 @Override
		 public void put(String key, String value) {
			this.delegate.addHeader(key, value);
		 }
	 }
}</programlisting>
<simpara>And you could register them like this:</simpara>
<programlisting language="java" linenumbering="unnumbered">@Bean HttpSpanInjector customHttpServletResponseSpanInjector() {
	return new CustomHttpServletResponseSpanInjector();
}

@Bean
HttpResponseInjectingTraceFilter responseInjectingTraceFilter(Tracer tracer) {
	return new HttpResponseInjectingTraceFilter(tracer, customHttpServletResponseSpanInjector());
}</programlisting>
</section>
<section xml:id="_tracefilter">
<title>TraceFilter</title>
<simpara>You can also modify the behaviour of the <literal>TraceFilter</literal> - the component that is responsible
for processing the input HTTP request and adding tags basing on the HTTP response. You can customize
the tags, or modify the response headers by registering your own instance of the <literal>TraceFilter</literal> bean.</simpara>
<simpara>In the following example we will register the <literal>TraceFilter</literal> bean and we will add the
<literal>ZIPKIN-TRACE-ID</literal> response header containing the current Span&#8217;s trace id. Also we will
add to the Span a tag with key <literal>custom</literal> and a value <literal>tag</literal>.</simpara>
<programlisting language="java" linenumbering="unnumbered">@Bean
TraceFilter myTraceFilter(BeanFactory beanFactory, final Tracer tracer) {
	return new TraceFilter(beanFactory) {
		@Override protected void addResponseTags(HttpServletResponse response,
				Throwable e) {
			// execute the default behaviour
			super.addResponseTags(response, e);
			// for readability we're returning trace id in a hex form
			response.addHeader("ZIPKIN-TRACE-ID",
					Span.idToHex(tracer.getCurrentSpan().getTraceId()));
			// we can also add some custom tags
			tracer.addTag("custom", "tag");
		}
	};
}</programlisting>
</section>
<section xml:id="_custom_sa_tag_in_zipkin">
<title>Custom SA tag in Zipkin</title>
<simpara>Sometimes you want to create a manual Span that will wrap a call to an external service which is not instrumented.
What you can do is to create a span with the <literal>peer.service</literal> tag that will contain a value of the service that you want to call.
Below you can see an example of a call to Redis that is wrapped in such a span.</simpara>
<programlisting language="java" linenumbering="unnumbered">org.springframework.cloud.sleuth.Span newSpan = tracer.createSpan("redis");
try {
	newSpan.tag("redis.op", "get");
	newSpan.tag("lc", "redis");
	newSpan.logEvent(org.springframework.cloud.sleuth.Span.CLIENT_SEND);
	// call redis service e.g
	// return (SomeObj) redisTemplate.opsForHash().get("MYHASH", someObjKey);
} finally {
	newSpan.tag("peer.service", "redisService");
	newSpan.tag("peer.ipv4", "1.2.3.4");
	newSpan.tag("peer.port", "1234");
	newSpan.logEvent(org.springframework.cloud.sleuth.Span.CLIENT_RECV);
	tracer.close(newSpan);
}</programlisting>
<important>
<simpara>Remember not to add both <literal>peer.service</literal> tag and the <literal>SA</literal> tag! You have to add only <literal>peer.service</literal>.</simpara>
</important>
</section>
<section xml:id="_custom_service_name">
<title>Custom service name</title>
<simpara>By default Sleuth assumes that when you send a span to Zipkin, you want the span&#8217;s service name
 to be equal to <literal>spring.application.name</literal> value. That&#8217;s not always the case though. There
 are situations in which you want to explicitly provide a different service name for all spans coming
 from your application. To achieve that it&#8217;s enough to just pass the following property
 to your application to override that value (example for <literal>foo</literal> service name):</simpara>
<programlisting language="yaml" linenumbering="unnumbered">spring.zipkin.service.name: foo</programlisting>
</section>
<section xml:id="_customization_of_reported_spans">
<title>Customization of reported spans</title>
<simpara>Before reporting spans to e.g. Zipkin you can be interested in modifying that span in some way.
 You can achieve that by using the <literal>SpanAdjuster</literal> interface.</simpara>
<simpara>Example of usage:</simpara>
<simpara>In Sleuth we&#8217;re generating spans with a fixed name. Some users want to modify the name depending on values
of tags. Implementation of the <literal>SpanAdjuster</literal> interface can be used to alter that name. Example:</simpara>
<programlisting language="yaml" linenumbering="unnumbered">@Bean
SpanAdjuster customSpanAdjuster() {
    return span -&gt; span.toBuilder().name(scrub(span.getName())).build();
}</programlisting>
<simpara>This will lead in changing the name of the reported span just before it gets sent to Zipkin.</simpara>
<important>
<simpara>Your <literal>SpanReporter</literal> should inject the <literal>SpanAdjuster</literal> and
 allow span manipulation before the actual reporting is done.</simpara>
</important>
</section>
<section xml:id="_host_locator">
<title>Host locator</title>
<simpara>In order to define the host that is corresponding to a particular span we need to resolve the host name
and port. The default approach is to take it from server properties. If those for some reason are not set
then we&#8217;re trying to retrieve the host name from the network interfaces.</simpara>
<simpara>If you have the discovery client enabled and prefer to retrieve the host address from the registered
instance in a service registry then you have to set the property (it&#8217;s applicable for both HTTP and
Stream based span reporting).</simpara>
<programlisting language="yaml" linenumbering="unnumbered">spring.zipkin.locator.discovery.enabled: true</programlisting>
</section>
</chapter>
<chapter xml:id="_span_data_as_messages">
<title>Span Data as Messages</title>
<simpara>You can accumulate and send span data over
<link xl:href="https://cloud.spring.io/spring-cloud-stream">Spring Cloud Stream</link> by
including the <literal>spring-cloud-sleuth-stream</literal> jar as a dependency, and
adding a Channel Binder implementation
(e.g. <literal>spring-cloud-starter-stream-rabbit</literal> for RabbitMQ or
<literal>spring-cloud-starter-stream-kafka</literal> for Kafka). This will
automatically turn your app into a producer of messages with payload
type <literal>Spans</literal>. The channel name to which the spans will be sent
is called <literal>sleuth</literal>.</simpara>
<section xml:id="_zipkin_consumer">
<title>Zipkin Consumer</title>
<simpara>There is a special convenience annotation for setting up a message consumer
for the Span data and pushing it into a Zipkin <literal>SpanStore</literal>. This application</simpara>
<programlisting language="java" linenumbering="unnumbered">@SpringBootApplication
@EnableZipkinStreamServer
public class Consumer {
	public static void main(String[] args) {
		SpringApplication.run(Consumer.class, args);
	}
}</programlisting>
<simpara>will listen for the Span data on whatever transport you provide via a
Spring Cloud Stream <literal>Binder</literal> (e.g. include
<literal>spring-cloud-starter-stream-rabbit</literal> for RabbitMQ, and similar
starters exist for Redis and Kafka). If you add the following UI dependency</simpara>
<programlisting language="xml" linenumbering="unnumbered">&lt;groupId&gt;io.zipkin.java&lt;/groupId&gt;
&lt;artifactId&gt;zipkin-autoconfigure-ui&lt;/artifactId&gt;</programlisting>
<simpara>Then you&#8217;ll have your app a
<link xl:href="https://github.com/openzipkin/zipkin">Zipkin server</link>, which hosts
the UI and api on port 9411.</simpara>
<simpara>The default <literal>SpanStore</literal> is in-memory (good for demos and getting
started quickly). For a more robust solution you can add MySQL and
<literal>spring-boot-starter-jdbc</literal> to your classpath and enable the JDBC
<literal>SpanStore</literal> via configuration, e.g.:</simpara>
<programlisting language="yaml" linenumbering="unnumbered">spring:
  rabbitmq:
    host: ${RABBIT_HOST:localhost}
  datasource:
    schema: classpath:/mysql.sql
    url: jdbc:mysql://${MYSQL_HOST:localhost}/test
    username: root
    password: root
# Switch this on to create the schema on startup:
    initialize: true
    continueOnError: true
  sleuth:
    enabled: false
zipkin:
  storage:
    type: mysql</programlisting>
<note>
<simpara>The <literal>@EnableZipkinStreamServer</literal> is also annotated with
<literal>@EnableZipkinServer</literal> so the process will also expose the standard
Zipkin server endpoints for collecting spans over HTTP, and for
querying in the Zipkin Web UI.</simpara>
</note>
</section>
<section xml:id="_custom_consumer">
<title>Custom Consumer</title>
<simpara>A custom consumer can also easily be implemented using
<literal>spring-cloud-sleuth-stream</literal> and binding to the <literal>SleuthSink</literal>. Example:</simpara>
<programlisting language="java" linenumbering="unnumbered">@EnableBinding(SleuthSink.class)
@SpringBootApplication(exclude = SleuthStreamAutoConfiguration.class)
@MessageEndpoint
public class Consumer {

    @ServiceActivator(inputChannel = SleuthSink.INPUT)
    public void sink(Spans input) throws Exception {
        // ... process spans
    }
}</programlisting>
<note>
<simpara>the sample consumer application above explicitly excludes
<literal>SleuthStreamAutoConfiguration</literal> so it doesn&#8217;t send messages to itself,
but this is optional (you might actually want to trace requests into
the consumer app).</simpara>
</note>
<simpara>In order to customize the polling mechanism you can create a bean of <literal>PollerMetadata</literal> type
with name equal to <literal>StreamSpanReporter.POLLER</literal>. Here you can find an example of such a configuration.</simpara>
<programlisting language="java" linenumbering="unnumbered">@Configuration
public static class CustomPollerConfiguration {

	@Bean(name = StreamSpanReporter.POLLER)
	PollerMetadata customPoller() {
		PollerMetadata poller = new PollerMetadata();
		poller.setMaxMessagesPerPoll(500);
		poller.setTrigger(new PeriodicTrigger(5000L));
		return poller;
	}
}</programlisting>
</section>
</chapter>
<chapter xml:id="_metrics">
<title>Metrics</title>
<simpara>Currently Spring Cloud Sleuth registers very simple metrics related to spans.
It&#8217;s using the <link xl:href="https://docs.spring.io/spring-boot/docs/current/reference/html/production-ready-metrics.html#production-ready-recording-metrics">Spring Boot&#8217;s metrics support</link>
to calculate the number of accepted and dropped spans. Each time a span gets
sent to Zipkin the number of accepted spans will increase. If there&#8217;s an error then
the number of dropped spans will get increased.</simpara>
</chapter>
<chapter xml:id="_integrations">
<title>Integrations</title>
<section xml:id="_runnable_and_callable">
<title>Runnable and Callable</title>
<simpara>If you&#8217;re wrapping your logic in <literal>Runnable</literal> or <literal>Callable</literal> it&#8217;s enough to wrap those classes in their Sleuth representative.</simpara>
<simpara>Example for <literal>Runnable</literal>:</simpara>
<programlisting language="java" linenumbering="unnumbered">Runnable runnable = new Runnable() {
	@Override
	public void run() {
		// do some work
	}

	@Override
	public String toString() {
		return "spanNameFromToStringMethod";
	}
};
// Manual `TraceRunnable` creation with explicit "calculateTax" Span name
Runnable traceRunnable = new TraceRunnable(tracer, spanNamer, runnable, "calculateTax");
// Wrapping `Runnable` with `Tracer`. The Span name will be taken either from the
// `@SpanName` annotation or from `toString` method
Runnable traceRunnableFromTracer = tracer.wrap(runnable);</programlisting>
<simpara>Example for <literal>Callable</literal>:</simpara>
<programlisting language="java" linenumbering="unnumbered">Callable&lt;String&gt; callable = new Callable&lt;String&gt;() {
	@Override
	public String call() throws Exception {
		return someLogic();
	}

	@Override
	public String toString() {
		return "spanNameFromToStringMethod";
	}
};
// Manual `TraceCallable` creation with explicit "calculateTax" Span name
Callable&lt;String&gt; traceCallable = new TraceCallable&lt;&gt;(tracer, spanNamer, callable, "calculateTax");
// Wrapping `Callable` with `Tracer`. The Span name will be taken either from the
// `@SpanName` annotation or from `toString` method
Callable&lt;String&gt; traceCallableFromTracer = tracer.wrap(callable);</programlisting>
<simpara>That way you will ensure that a new Span is created and closed for each execution.</simpara>
</section>
<section xml:id="_hystrix">
<title>Hystrix</title>
<section xml:id="_custom_concurrency_strategy">
<title>Custom Concurrency Strategy</title>
<simpara>We&#8217;re registering a custom <link xl:href="https://github.com/Netflix/Hystrix/wiki/Plugins#concurrencystrategy"><literal>HystrixConcurrencyStrategy</literal></link>
that wraps all <literal>Callable</literal> instances into their Sleuth representative -
the <literal>TraceCallable</literal>. The strategy either starts or continues a span depending on the fact whether tracing was already going
on before the Hystrix command was called. To disable the custom Hystrix Concurrency Strategy set the <literal>spring.sleuth.hystrix.strategy.enabled</literal> to <literal>false</literal>.</simpara>
</section>
<section xml:id="_manual_command_setting">
<title>Manual Command setting</title>
<simpara>Assuming that you have the following <literal>HystrixCommand</literal>:</simpara>
<programlisting language="java" linenumbering="unnumbered">HystrixCommand&lt;String&gt; hystrixCommand = new HystrixCommand&lt;String&gt;(setter) {
	@Override
	protected String run() throws Exception {
		return someLogic();
	}
};</programlisting>
<simpara>In order to pass the tracing information you have to wrap the same logic in the Sleuth version of the <literal>HystrixCommand</literal> which is the
<literal>TraceCommand</literal>:</simpara>
<programlisting language="java" linenumbering="unnumbered">TraceCommand&lt;String&gt; traceCommand = new TraceCommand&lt;String&gt;(tracer, traceKeys, setter) {
	@Override
	public String doRun() throws Exception {
		return someLogic();
	}
};</programlisting>
</section>
</section>
<section xml:id="_rxjava">
<title>RxJava</title>
<simpara>We&#8217;re registering a custom <link xl:href="https://github.com/ReactiveX/RxJava/wiki/Plugins#rxjavaschedulershook"><literal>RxJavaSchedulersHook</literal></link>
that wraps all <literal>Action0</literal> instances into their Sleuth representative -
the <literal>TraceAction</literal>. The hook either starts or continues a span depending on the fact whether tracing was already going
on before the Action was scheduled. To disable the custom RxJavaSchedulersHook set the <literal>spring.sleuth.rxjava.schedulers.hook.enabled</literal> to <literal>false</literal>.</simpara>
<simpara>You can define a list of regular expressions for thread names, for which you don&#8217;t want a Span to be created. Just provide a comma separated list
of regular expressions in the <literal>spring.sleuth.rxjava.schedulers.ignoredthreads</literal> property.</simpara>
</section>
<section xml:id="_http_integration">
<title>HTTP integration</title>
<simpara>Features from this section can be disabled by providing the <literal>spring.sleuth.web.enabled</literal> property with value equal to <literal>false</literal>.</simpara>
<section xml:id="_http_filter">
<title>HTTP Filter</title>
<simpara>Via the <literal>TraceFilter</literal> all sampled incoming requests result in creation of a Span. That Span&#8217;s name is <literal>http:</literal> + the path to which
 the request was sent. E.g. if the request was sent to <literal>/foo/bar</literal> then the name will be <literal>http:/foo/bar</literal>. You can configure which URIs you would
 like to skip via the <literal>spring.sleuth.web.skipPattern</literal> property. If you have <literal>ManagementServerProperties</literal> on classpath then
 its value of <literal>contextPath</literal> gets appended to the provided skip pattern.</simpara>
</section>
<section xml:id="_handlerinterceptor">
<title>HandlerInterceptor</title>
<simpara>Since we want the span names to be precise we&#8217;re using a <literal>TraceHandlerInterceptor</literal> that either wraps an
 existing <literal>HandlerInterceptor</literal> or is added directly to the list of existing <literal>HandlerInterceptors</literal>. The
 <literal>TraceHandlerInterceptor</literal> adds a special request attribute to the given <literal>HttpServletRequest</literal>. If the
 the <literal>TraceFilter</literal> doesn&#8217;t see this attribute set it will create a "fallback" span which is an additional
 span created on the server side so that the trace is presented properly in the UI. Seeing that most likely
 signifies that there is a missing instrumentation. In that case please file an issue in Spring Cloud Sleuth.</simpara>
</section>
<section xml:id="_async_servlet_support">
<title>Async Servlet support</title>
<simpara>If your controller returns a <literal>Callable</literal> or a <literal>WebAsyncTask</literal> Spring Cloud Sleuth will continue the existing span instead of creating a new one.</simpara>
</section>
</section>
<section xml:id="_http_client_integration">
<title>HTTP client integration</title>
<section xml:id="_synchronous_rest_template">
<title>Synchronous Rest Template</title>
<simpara>We&#8217;re injecting a <literal>RestTemplate</literal> interceptor that ensures that all the tracing information is passed to the requests. Each time a
call is made a new Span is created. It gets closed upon receiving the response. In order to block the synchronous <literal>RestTemplate</literal> features
just set <literal>spring.sleuth.web.client.enabled</literal> to <literal>false</literal>.</simpara>
<important>
<simpara>You have to register <literal>RestTemplate</literal> as a bean so that the interceptors will get injected.
If you create a <literal>RestTemplate</literal> instance with a <literal>new</literal> keyword then the instrumentation WILL NOT work.</simpara>
</important>
</section>
<section xml:id="_asynchronous_rest_template">
<title>Asynchronous Rest Template</title>
<important>
<simpara>A traced version of an <literal>AsyncRestTemplate</literal> bean is registered for you out of the box. If you
have your own bean you have to wrap it in a <literal>TraceAsyncRestTemplate</literal> representation. The best solution
is to only customize the <literal>ClientHttpRequestFactory</literal> and / or <literal>AsyncClientHttpRequestFactory</literal>.
<emphasis role="strong">If you have your own <literal>AsyncRestTemplate</literal> and you don&#8217;t wrap it your calls WILL NOT GET TRACED</emphasis>.</simpara>
</important>
<simpara>Custom instrumentation is set to create and close Spans upon sending and receiving requests. You can customize the <literal>ClientHttpRequestFactory</literal>
and the <literal>AsyncClientHttpRequestFactory</literal> by registering your beans. Remember to use tracing compatible implementations (e.g. don&#8217;t forget to
wrap <literal>ThreadPoolTaskScheduler</literal> in a <literal>TraceAsyncListenableTaskExecutor</literal>). Example of custom request factories:</simpara>
<programlisting language="java" linenumbering="unnumbered">@EnableAutoConfiguration
@Configuration
public static class TestConfiguration {

	@Bean
	ClientHttpRequestFactory mySyncClientFactory() {
		return new MySyncClientHttpRequestFactory();
	}

	@Bean
	AsyncClientHttpRequestFactory myAsyncClientFactory() {
		return new MyAsyncClientHttpRequestFactory();
	}
}</programlisting>
<simpara>To block the <literal>AsyncRestTemplate</literal> features set <literal>spring.sleuth.web.async.client.enabled</literal> to <literal>false</literal>.
To disable creation of the default <literal>TraceAsyncClientHttpRequestFactoryWrapper</literal> set <literal>spring.sleuth.web.async.client.factory.enabled</literal>
to <literal>false</literal>. If you don&#8217;t want to create <literal>AsyncRestClient</literal> at all set <literal>spring.sleuth.web.async.client.template.enabled</literal> to <literal>false</literal>.</simpara>
<section xml:id="_multiple_asynchronous_rest_templates">
<title>Multiple Asynchronous Rest Templates</title>
<simpara>Sometimes you need to use multiple implementations of Asynchronous Rest Template. In the following snippet you
can see an example of how to set up such a custom <literal>AsyncRestTemplate</literal>.</simpara>
<programlisting language="java" linenumbering="unnumbered">@Configuration
@EnableAutoConfiguration
static class Config {
	@Autowired Tracer tracer;
	@Autowired HttpTraceKeysInjector httpTraceKeysInjector;
	@Autowired HttpSpanInjector spanInjector;

	@Bean(name = "customAsyncRestTemplate")
	public AsyncRestTemplate traceAsyncRestTemplate(@Qualifier("customHttpRequestFactoryWrapper")
			TraceAsyncClientHttpRequestFactoryWrapper wrapper) {
		return new TraceAsyncRestTemplate(wrapper, this.tracer);
	}

	@Bean(name = "customHttpRequestFactoryWrapper")
	public TraceAsyncClientHttpRequestFactoryWrapper traceAsyncClientHttpRequestFactory() {
		return new TraceAsyncClientHttpRequestFactoryWrapper(this.tracer,
				this.spanInjector,
				asyncClientFactory(),
				clientHttpRequestFactory(),
				this.httpTraceKeysInjector);
	}

	private ClientHttpRequestFactory clientHttpRequestFactory() {
		ClientHttpRequestFactory clientHttpRequestFactory = new CustomClientHttpRequestFactory();
		//CUSTOMIZE HERE
		return clientHttpRequestFactory;
	}

	private AsyncClientHttpRequestFactory asyncClientFactory() {
		AsyncClientHttpRequestFactory factory = new CustomAsyncClientHttpRequestFactory();
		//CUSTOMIZE HERE
		return factory;
	}
}</programlisting>
</section>
</section>
<section xml:id="_traverson">
<title>Traverson</title>
<simpara>If you&#8217;re using the <link xl:href="https://docs.spring.io/spring-hateoas/docs/current/reference/html/#client.traverson">Traverson</link> library
it&#8217;s enough for you to inject a <literal>RestTemplate</literal> as a bean into your Traverson object. Since <literal>RestTemplate</literal>
is already intercepted, you will get full support of tracing in your client. Below you can find a pseudo code
of how to do that:</simpara>
<programlisting language="java" linenumbering="unnumbered">@Autowired RestTemplate restTemplate;

Traverson traverson = new Traverson(URI.create("http://some/address"),
    MediaType.APPLICATION_JSON, MediaType.APPLICATION_JSON_UTF8).setRestOperations(restTemplate);
// use Traverson</programlisting>
</section>
</section>
<section xml:id="_feign">
<title>Feign</title>
<simpara>By default Spring Cloud Sleuth provides integration with feign via the <literal>TraceFeignClientAutoConfiguration</literal>. You can disable it entirely
by setting <literal>spring.sleuth.feign.enabled</literal> to false. If you do so then no Feign related instrumentation will take place.</simpara>
<simpara>Part of Feign instrumentation is done via a <literal>FeignBeanPostProcessor</literal>. You can disable it by providing the <literal>spring.sleuth.feign.processor.enabled</literal> equal to <literal>false</literal>.
If you set it like this then Spring Cloud Sleuth will not instrument any of your custom Feign components. All the default instrumentation
however will be still there.</simpara>
</section>
<section xml:id="_asynchronous_communication">
<title>Asynchronous communication</title>
<section xml:id="__async_annotated_methods">
<title>@Async annotated methods</title>
<simpara>In Spring Cloud Sleuth we&#8217;re instrumenting async related components so that the tracing information is passed between threads.
You can disable this behaviour by setting the value of <literal>spring.sleuth.async.enabled</literal> to <literal>false</literal>.</simpara>
<simpara>If you annotate your method with <literal>@Async</literal> then we&#8217;ll automatically create a new Span with the following characteristics:</simpara>
<itemizedlist>
<listitem>
<simpara>the Span name will be the annotated method name</simpara>
</listitem>
<listitem>
<simpara>the Span will be tagged with that method&#8217;s class name and the method name too</simpara>
</listitem>
</itemizedlist>
</section>
<section xml:id="__scheduled_annotated_methods">
<title>@Scheduled annotated methods</title>
<simpara>In Spring Cloud Sleuth we&#8217;re instrumenting scheduled method execution so that the tracing information is passed between threads. You can disable this behaviour
by setting the value of <literal>spring.sleuth.scheduled.enabled</literal> to <literal>false</literal>.</simpara>
<simpara>If you annotate your method with <literal>@Scheduled</literal> then we&#8217;ll automatically create a new Span with the following characteristics:</simpara>
<itemizedlist>
<listitem>
<simpara>the Span name will be the annotated method name</simpara>
</listitem>
<listitem>
<simpara>the Span will be tagged with that method&#8217;s class name and the method name too</simpara>
</listitem>
</itemizedlist>
<simpara>If you want to skip Span creation for some <literal>@Scheduled</literal> annotated classes you can set the
<literal>spring.sleuth.scheduled.skipPattern</literal> with a regular expression that will match the fully qualified name of the
<literal>@Scheduled</literal> annotated class.</simpara>
<tip>
<simpara>If you are using <literal>spring-cloud-sleuth-stream</literal> and <literal>spring-cloud-netflix-hystrix-stream</literal> together, Span will be created for each Hystrix metrics and sent to Zipkin. This may be annoying. You can prevent this by setting <literal>spring.sleuth.scheduled.skipPattern=org.springframework.cloud.netflix.hystrix.stream.HystrixStreamTask</literal></simpara>
</tip>
</section>
<section xml:id="_executor_executorservice_and_scheduledexecutorservice">
<title>Executor, ExecutorService and ScheduledExecutorService</title>
<simpara>We&#8217;re providing <literal>LazyTraceExecutor</literal>, <literal>TraceableExecutorService</literal> and <literal>TraceableScheduledExecutorService</literal>. Those implementations
are creating Spans each time a new task is submitted, invoked or scheduled.</simpara>
<simpara>Here you can see an example of how to pass tracing information with <literal>TraceableExecutorService</literal> when working with <literal>CompletableFuture</literal>:</simpara>
<programlisting language="java" linenumbering="unnumbered">CompletableFuture&lt;Long&gt; completableFuture = CompletableFuture.supplyAsync(() -&gt; {
	// perform some logic
	return 1_000_000L;
}, new TraceableExecutorService(executorService,
		// 'calculateTax' explicitly names the span - this param is optional
		tracer, traceKeys, spanNamer, "calculateTax"));</programlisting>
<important>
<simpara>Sleuth doesn&#8217;t work with <literal>parallelStream()</literal> out of the box. If you want
to have the tracing information propagated through the stream you have to use the
approach with <literal>supplyAsync(...)</literal> as presented above.</simpara>
</important>
<section xml:id="_customization_of_executors">
<title>Customization of Executors</title>
<simpara>Sometimes you need to set up a custom instance of the <literal>AsyncExecutor</literal>. In the following snippet you
can see an example of how to set up such a custom <literal>Executor</literal>.</simpara>
<programlisting language="java" linenumbering="unnumbered">@Configuration
@EnableAutoConfiguration
@EnableAsync
static class CustomExecutorConfig extends AsyncConfigurerSupport {

	@Autowired BeanFactory beanFactory;

	@Override public Executor getAsyncExecutor() {
		ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
		// CUSTOMIZE HERE
		executor.setCorePoolSize(7);
		executor.setMaxPoolSize(42);
		executor.setQueueCapacity(11);
		executor.setThreadNamePrefix("MyExecutor-");
		// DON'T FORGET TO INITIALIZE
		executor.initialize();
		return new LazyTraceExecutor(this.beanFactory, executor);
	}
}</programlisting>
</section>
</section>
</section>
<section xml:id="_messaging">
<title>Messaging</title>
<simpara>Spring Cloud Sleuth integrates with <link xl:href="https://projects.spring.io/spring-integration/">Spring Integration</link>. It creates spans for publish and
subscribe events. To disable Spring Integration instrumentation, set <literal>spring.sleuth.integration.enabled</literal> to false.</simpara>
<simpara>You can provide the <literal>spring.sleuth.integration.patterns</literal> pattern to explicitly
provide the names of channels that you want to include for tracing. By default all channels
are included.</simpara>
<important>
<simpara>When using the <literal>Executor</literal> to build a Spring Integration <literal>IntegrationFlow</literal> remember to use the <emphasis role="strong">untraced</emphasis> version of the <literal>Executor</literal>.
Decorating Spring Integration Executor Channel with <literal>TraceableExecutorService</literal> will cause the spans to be improperly closed.</simpara>
</important>
</section>
<section xml:id="_zuul">
<title>Zuul</title>
<simpara>We&#8217;re registering Zuul filters to propagate the tracing information (the request header is enriched with tracing data).
To disable Zuul support set the <literal>spring.sleuth.zuul.enabled</literal> property to <literal>false</literal>.</simpara>
</section>
</chapter>
<chapter xml:id="_running_examples">
<title>Running examples</title>
<simpara>You can find the running examples deployed in the <link xl:href="https://run.pivotal.io/">Pivotal Web Services</link>. Check them out in the following links:</simpara>
<itemizedlist>
<listitem>
<simpara><link xl:href="https://docssleuth-zipkin-server.cfapps.io/">Zipkin for apps presented in the samples to the top</link></simpara>
</listitem>
<listitem>
<simpara><link xl:href="https://docsbrewing-zipkin-web.cfapps.io/">Zipkin for Brewery on PWS</link>, its <link xl:href="https://github.com/spring-cloud-samples/brewery">Github Code</link></simpara>
</listitem>
</itemizedlist>
</chapter>
</book>