53 lines
9.2 KiB
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53 lines
9.2 KiB
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<title>53. Sampling</title><link rel="stylesheet" type="text/css" href="css/manual-multipage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="multi_spring-cloud.html" title="Spring Cloud"><link rel="up" href="multi__spring_cloud_sleuth.html" title="Part VIII. Spring Cloud Sleuth"><link rel="prev" href="multi__features_2.html" title="52. Features"><link rel="next" href="multi__propagation.html" title="54. Propagation"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">53. Sampling</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi__features_2.html">Prev</a> </td><th width="60%" align="center">Part VIII. Spring Cloud Sleuth</th><td width="20%" align="right"> <a accesskey="n" href="multi__propagation.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a name="_sampling" href="#_sampling"></a>53. Sampling</h2></div></div></div><p>Sampling may be employed to reduce the data collected and reported out of process.
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When a span is not sampled, it adds no overhead (a noop).</p><p>Sampling is an up-front decision, meaning that the decision to report data is made at the first operation in a trace and that decision is propagated downstream.</p><p>By default, a global sampler applies a single rate to all traced operations.
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<code class="literal">Tracer.Builder.sampler</code> controls this setting, and it defaults to tracing every request.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_declarative_sampling" href="#_declarative_sampling"></a>53.1 Declarative sampling</h2></div></div></div><p>Some applications need to sample based on the type or annotations of a java method.</p><p>Most users use a framework interceptor to automate this sort of policy.
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The following example shows how that might work internally:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Autowired</span></em> Tracer tracer;
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">// derives a sample rate from an annotation on a java method</span>
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DeclarativeSampler<Traced> sampler = DeclarativeSampler.create(Traced::sampleRate);
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<em><span class="hl-annotation" style="color: gray">@Around("@annotation(traced)")</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> Object traceThing(ProceedingJoinPoint pjp, Traced traced) <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">throws</span> Throwable {
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">// When there is no trace in progress, this decides using an annotation</span>
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Sampler decideUsingAnnotation = declarativeSampler.toSampler(traced);
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Tracer tracer = tracer.withSampler(decideUsingAnnotation);
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">// This code looks the same as if there was no declarative override</span>
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ScopedSpan span = tracer.startScopedSpan(spanName(pjp));
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">try</span> {
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> pjp.proceed();
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} <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">catch</span> (RuntimeException | Error e) {
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span.error(e);
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">throw</span> e;
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} <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">finally</span> {
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span.finish();
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}
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}</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_custom_sampling" href="#_custom_sampling"></a>53.2 Custom sampling</h2></div></div></div><p>Depending on what the operation is, you may want to apply different policies.
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For example, you might not want to trace requests to static resources such as images, or you might want to trace all requests to a new api.</p><p>Most users use a framework interceptor to automate this sort of policy.
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The following example shows how that might work internally:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Autowired</span></em> Tracer tracer;
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<em><span class="hl-annotation" style="color: gray">@Autowired</span></em> Sampler fallback;
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Span nextSpan(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">final</span> Request input) {
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Sampler requestBased = Sampler() {
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<em><span class="hl-annotation" style="color: gray">@Override</span></em> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">boolean</span> isSampled(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">long</span> traceId) {
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">if</span> (input.url().startsWith(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"/experimental"</span>)) {
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> true;
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} <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">else</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">if</span> (input.url().startsWith(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"/static"</span>)) {
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> false;
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}
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> fallback.isSampled(traceId);
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}
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};
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> tracer.withSampler(requestBased).nextSpan();
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}</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_sampling_in_spring_cloud_sleuth" href="#_sampling_in_spring_cloud_sleuth"></a>53.3 Sampling in Spring Cloud Sleuth</h2></div></div></div><p>By default Spring Cloud Sleuth sets all spans to non-exportable.
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That means that traces appear in logs but not in any remote store.
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For testing the default is often enough, and it probably is all you need if you use only the logs (for example, with an ELK aggregator).
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If you export span data to Zipkin, there is also an <code class="literal">Sampler.ALWAYS_SAMPLE</code> setting that exports everything and a <code class="literal">ProbabilityBasedSampler</code> setting that samples a fixed fraction of spans.</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 <code class="literal">ProbabilityBasedSampler</code> is the default if you use <code class="literal">spring-cloud-sleuth-zipkin</code>.
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You can configure the exports by setting <code class="literal">spring.sleuth.sampler.probability</code>.
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The passed value needs to be a double from <code class="literal">0.0</code> to <code class="literal">1.0</code>.</p></td></tr></table></div><p>A sampler can be installed by creating a bean definition, as shown in the following example:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Bean</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> Sampler defaultSampler() {
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> Sampler.ALWAYS_SAMPLE;
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}</pre><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Tip"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="images/tip.png"></td><th align="left">Tip</th></tr><tr><td align="left" valign="top"><p>You can set the HTTP header <code class="literal">X-B3-Flags</code> to <code class="literal">1</code>, or, when doing messaging, you can set the <code class="literal">spanFlags</code> header to <code class="literal">1</code>.
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Doing so forces the current span to be exportable regardless of the sampling decision.</p></td></tr></table></div><p>In order to use the rate-limited sampler set the <code class="literal">spring.sleuth.sampler.rate</code> property to choose an amount of traces to accept on a per-second interval. The minimum number is 0 and the max is 2,147,483,647 (max int).</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi__features_2.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="multi__spring_cloud_sleuth.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="multi__propagation.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">52. Features </td><td width="20%" align="center"><a accesskey="h" href="multi_spring-cloud.html">Home</a></td><td width="40%" align="right" valign="top"> 54. Propagation</td></tr></table></div></body></html> |