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126 lines
21 KiB
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<html><head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>Spring Cloud Bus</title><link rel="stylesheet" type="text/css" href="css/manual-singlepage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div lang="en" class="book"><div class="titlepage"><div><div><h1 class="title"><a name="d0e3"></a>Spring Cloud Bus</h1></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="preface"><a href="#d0e9"></a></span></dt><dt><span class="chapter"><a href="#_quick_start">1. Quick Start</a></span></dt><dt><span class="chapter"><a href="#_addressing_an_instance">2. Addressing an Instance</a></span></dt><dt><span class="chapter"><a href="#_addressing_all_instances_of_a_service">3. Addressing All Instances of a Service</a></span></dt><dt><span class="chapter"><a href="#_service_id_must_be_unique">4. Service ID Must Be Unique</a></span></dt><dt><span class="chapter"><a href="#_customizing_the_message_broker">5. Customizing the Message Broker</a></span></dt><dt><span class="chapter"><a href="#_tracing_bus_events">6. Tracing Bus Events</a></span></dt><dt><span class="chapter"><a href="#_broadcasting_your_own_events">7. Broadcasting Your Own Events</a></span></dt><dd><dl><dt><span class="section"><a href="#_registering_events_in_custom_packages">7.1. Registering events in custom packages</a></span></dt></dl></dd></dl></div><div class="preface"><div class="titlepage"><div><div><h1 class="title"><a name="d0e9" href="#d0e9"></a></h1></div></div></div><p>Spring Cloud Bus links the nodes of a distributed system with a lightweight message
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broker. This broker can then be used to broadcast state changes (such as configuration
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changes) or other management instructions. A key idea is that the bus is like a
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distributed actuator for a Spring Boot application that is scaled out. However, it can
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also be used as a communication channel between apps. This project provides starters for
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either an AMQP broker or Kafka as the transport.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>Spring Cloud is released under the non-restrictive Apache 2.0 license. If you would like to contribute to this section of the documentation or if you find an error, please find the source code and issue trackers in the project at <a class="link" href="https://github.com/spring-cloud/spring-cloud-config/tree/master/docs/src/main/asciidoc" target="_top">github</a>.</p></td></tr></table></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_quick_start" href="#_quick_start"></a>1. Quick Start</h1></div></div></div><p>Spring Cloud Bus works by adding Spring Boot autconfiguration if it detects itself on the
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classpath. To enable the bus, add <code class="literal">spring-cloud-starter-bus-amqp</code> or
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<code class="literal">spring-cloud-starter-bus-kafka</code> to your dependency management. Spring Cloud takes care of
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the rest. Make sure the broker (RabbitMQ or Kafka) is available and configured. When
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running on localhost, you need not do anything. If you run remotely, use Spring Cloud
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Connectors or Spring Boot conventions to define the broker credentials, as shown in the
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following example for Rabbit:</p><p><b>application.yml. </b>
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</p><pre class="screen">spring:
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rabbitmq:
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host: mybroker.com
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port: 5672
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username: user
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password: secret</pre><p>
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</p><p>The bus currently supports sending messages to all nodes listening or all nodes for a
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particular service (as defined by Eureka). The <code class="literal">/bus/*</code> actuator namespace has some HTTP
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endpoints. Currently, two are implemented. The first, <code class="literal">/bus/env</code>, sends key/value pairs to
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update each node’s Spring Environment. The second, <code class="literal">/bus/refresh</code>, reloads each
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application’s configuration, as though they had all been pinged on their <code class="literal">/refresh</code>
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endpoint.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>The Spring Cloud Bus starters cover Rabbit and Kafka, because those are the two most
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common implementations. However, Spring Cloud Stream is quite flexible, and the binder
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works with <code class="literal">spring-cloud-bus</code>.</p></td></tr></table></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_addressing_an_instance" href="#_addressing_an_instance"></a>2. Addressing an Instance</h1></div></div></div><p>Each instance of the application has a service ID, whose value can be set with
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<code class="literal">spring.cloud.bus.id</code> and whose value is expected to be a colon-separated list of
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identifiers, in order from least specific to most specific. The default value is
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constructed from the environment as a combination of the <code class="literal">spring.application.name</code> and
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<code class="literal">server.port</code> (or <code class="literal">spring.application.index</code>, if set). The default value of the ID is
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constructed in the form of <code class="literal">app:index:id</code>, where:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="literal">app</code> is the <code class="literal">vcap.application.name</code>, if it exists, or <code class="literal">spring.application.name</code></li><li class="listitem"><code class="literal">index</code> is the <code class="literal">vcap.application.instance_index</code>, if it exists,
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<code class="literal">spring.application.index</code>, <code class="literal">local.server.port</code>, <code class="literal">server.port</code>, or <code class="literal">0</code> (in that order).</li><li class="listitem"><code class="literal">id</code> is the <code class="literal">vcap.application.instance_id</code>, if it exists, or a random value.</li></ul></div><p>The HTTP endpoints accept a “destination” parameter, such as
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<code class="literal">/bus/refresh?destination=customers:9000</code>, where <code class="literal">destination</code> is a service ID. If the ID
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is owned by an instance on the bus, it processes the message, and all other instances
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ignore it.</p></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_addressing_all_instances_of_a_service" href="#_addressing_all_instances_of_a_service"></a>3. Addressing All Instances of a Service</h1></div></div></div><p>The “destination” parameter is used in a Spring <code class="literal">PathMatcher</code> (with the path separator
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as a colon — <code class="literal">:</code>) to determine if an instance processes the message. Using the example
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from earlier, <code class="literal">/bus/refresh?destination=customers:**</code> targets all instances of the
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“customers” service regardless of the rest of the service ID.</p></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_service_id_must_be_unique" href="#_service_id_must_be_unique"></a>4. Service ID Must Be Unique</h1></div></div></div><p>The bus tries twice to eliminate processing an event — once from the original
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<code class="literal">ApplicationEvent</code> and once from the queue. To do so, it checks the sending service ID
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against the current service ID. If multiple instances of a service have the same ID,
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events are not processed. When running on a local machine, each service is on a different
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port, and that port is part of the ID. Cloud Foundry supplies an index to differentiate.
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To ensure that the ID is unique outside Cloud Foundry, set <code class="literal">spring.application.index</code> to
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something unique for each instance of a service.</p></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_customizing_the_message_broker" href="#_customizing_the_message_broker"></a>5. Customizing the Message Broker</h1></div></div></div><p>Spring Cloud Bus uses <a class="link" href="https://cloud.spring.io/spring-cloud-stream" target="_top">Spring Cloud Stream</a> to
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broadcast the messages. So, to get messages to flow, you need only include the binder
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implementation of your choice in the classpath. There are convenient starters for the bus
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with AMQP (RabbitMQ) and Kafka (<code class="literal">spring-cloud-starter-bus-[amqp|kafka]</code>). Generally
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speaking, Spring Cloud Stream relies on Spring Boot autoconfiguration conventions for
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configuring middleware. For instance, the AMQP broker address can be changed with
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<code class="literal">spring.rabbitmq.*</code> configuration properties. Spring Cloud Bus has a handful of
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native configuration properties in <code class="literal">spring.cloud.bus.*</code> (for example,
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<code class="literal">spring.cloud.bus.destination</code> is the name of the topic to use as the external
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middleware). Normally, the defaults suffice.</p><p>To learn more about how to customize the message broker settings, consult the Spring Cloud
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Stream documentation.</p></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_tracing_bus_events" href="#_tracing_bus_events"></a>6. Tracing Bus Events</h1></div></div></div><p>Bus events (subclasses of <code class="literal">RemoteApplicationEvent</code>) can be traced by setting
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<code class="literal">spring.cloud.bus.trace.enabled=true</code>. If you do so, the Spring Boot <code class="literal">TraceRepository</code>
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(if it is present) shows each event sent and all the acks from each service instance. The
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following example comes from the <code class="literal">/trace</code> endpoint:</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">{</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"timestamp"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"2015-11-26T10:24:44.411+0000"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"info"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">{</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"signal"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"spring.cloud.bus.ack"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"type"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"RefreshRemoteApplicationEvent"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"id"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"c4d374b7-58ea-4928-a312-31984def293b"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"origin"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"stores:8081"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"destination"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"*:**"</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">}</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">},</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">{</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"timestamp"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"2015-11-26T10:24:41.864+0000"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"info"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">{</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"signal"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"spring.cloud.bus.sent"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"type"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"RefreshRemoteApplicationEvent"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"id"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"c4d374b7-58ea-4928-a312-31984def293b"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"origin"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"customers:9000"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"destination"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"*:**"</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">}</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">},</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">{</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"timestamp"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"2015-11-26T10:24:41.862+0000"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"info"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">{</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"signal"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"spring.cloud.bus.ack"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"type"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"RefreshRemoteApplicationEvent"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"id"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"c4d374b7-58ea-4928-a312-31984def293b"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"origin"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"customers:9000"</span><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">,</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"destination"</span>: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"*:**"</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">}</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">}</span></pre><p>The preceding trace shows that a <code class="literal">RefreshRemoteApplicationEvent</code> was sent from
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<code class="literal">customers:9000</code>, broadcast to all services, and received (acked) by <code class="literal">customers:9000</code> and
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<code class="literal">stores:8081</code>.</p><p>To handle the ack signals yourself, you could add an <code class="literal">@EventListener</code> for the
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<code class="literal">AckRemoteApplicationEvent</code> and <code class="literal">SentApplicationEvent</code> types to your app (and enable
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tracing). Alternatively, you could tap into the <code class="literal">TraceRepository</code> and mine the data from
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there.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>Any Bus application can trace acks. However, sometimes, it is
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useful to do this in a central service that can do more complex
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queries on the data or forward it to a specialized tracing service.</p></td></tr></table></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_broadcasting_your_own_events" href="#_broadcasting_your_own_events"></a>7. Broadcasting Your Own Events</h1></div></div></div><p>The Bus can carry any event of type <code class="literal">RemoteApplicationEvent</code>. The default transport is
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JSON, and the deserializer needs to know which types are going to be used ahead of time.
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To register a new type, you must put it in a subpackage of
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<code class="literal">org.springframework.cloud.bus.event</code>.</p><p>To customise the event name, you can use <code class="literal">@JsonTypeName</code> on your custom class or rely on
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the default strategy, which is to use the simple name of the class.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>Both the producer and the consumer need access to the class definition.</p></td></tr></table></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_registering_events_in_custom_packages" href="#_registering_events_in_custom_packages"></a>7.1 Registering events in custom packages</h2></div></div></div><p>If you cannot or do not want to use a subpackage of <code class="literal">org.springframework.cloud.bus.event</code>
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for your custom events, you must specify which packages to scan for events of type
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<code class="literal">RemoteApplicationEvent</code> by using the <code class="literal">@RemoteApplicationEventScan</code> annotation. Packages
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specified with <code class="literal">@RemoteApplicationEventScan</code> include subpackages.</p><p>For example, consider the following custom event, called <code class="literal">MyEvent</code>:</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">package</span> com.acme;
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> MyEvent <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">extends</span> RemoteApplicationEvent {
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...
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}</pre><p>You can register that event with the deserializer in the following way:</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">package</span> com.acme;
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<em><span class="hl-annotation" style="color: gray">@Configuration</span></em>
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<em><span class="hl-annotation" style="color: gray">@RemoteApplicationEventScan</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> BusConfiguration {
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...
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}</pre><p>Without specifying a value, the package of the class where <code class="literal">@RemoteApplicationEventScan</code>
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is used is registered. In this example, <code class="literal">com.acme</code> is registered by using the package of
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<code class="literal">BusConfiguration</code>.</p><p>You can also explicitly specify the packages to scan by using the <code class="literal">value</code>, <code class="literal">basePackages</code>
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or <code class="literal">basePackageClasses</code> properties on <code class="literal">@RemoteApplicationEventScan</code>, as shown in the
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following example:</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">package</span> com.acme;
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<em><span class="hl-annotation" style="color: gray">@Configuration</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">//@RemoteApplicationEventScan({"com.acme", "foo.bar"})</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">//@RemoteApplicationEventScan(basePackages = {"com.acme", "foo.bar", "fizz.buzz"})</span>
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<em><span class="hl-annotation" style="color: gray">@RemoteApplicationEventScan(basePackageClasses = BusConfiguration.class)</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> BusConfiguration {
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...
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}</pre><p>All of the preceding examples of <code class="literal">@RemoteApplicationEventScan</code> are equivalent, in that the
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<code class="literal">com.acme</code> package is registered by explicitly specifying the packages on
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<code class="literal">@RemoteApplicationEventScan</code>.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>You can specify multiple base packages to scan.</p></td></tr></table></div></div></div></div></body></html> |