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<title>Introduction</title> |
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</head> |
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<body class="book toc2 toc-left"> |
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<div id="header"> |
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<div id="toc" class="toc2"> |
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<div id="toctitle">Table of Contents</div> |
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<ul class="sectlevel1"> |
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<li><a href="#_introduction">Introduction</a> |
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<ul class="sectlevel2"> |
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<li><a href="#_supported_implementations">Supported Implementations</a></li> |
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</ul> |
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</li> |
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<li><a href="#_core_concepts">Core Concepts</a> |
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<ul class="sectlevel2"> |
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<li><a href="#_circuit_breakers_in_reactive_code">Circuit Breakers In Reactive Code</a></li> |
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</ul> |
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</li> |
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<li><a href="#_configuration">Configuration</a></li> |
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</ul> |
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</div> |
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</div> |
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<div id="content"> |
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<div class="sect1"> |
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<h2 id="_introduction"><a class="link" href="#_introduction">Introduction</a></h2> |
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<div class="sectionbody"> |
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<div class="paragraph"> |
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<p>Spring Cloud Circuit breaker provides an abstraction across different circuit breaker implementations. |
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It provides a consistent API to use in your applications, letting you, the developer, choose the circuit breaker implementation that best fits your needs for your application.</p> |
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</div> |
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<div class="sect2"> |
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<h3 id="_supported_implementations"><a class="link" href="#_supported_implementations">Supported Implementations</a></h3> |
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<div class="paragraph"> |
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<p>Spring Cloud supports the following circuit-breaker implementations:</p> |
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</div> |
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<div class="ulist"> |
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<ul> |
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<li> |
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<p><a href="https://github.com/resilience4j/resilience4j">Resilience4J</a></p> |
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</li> |
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<li> |
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<p><a href="https://github.com/alibaba/Sentinel">Sentinel</a></p> |
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</li> |
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<li> |
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<p><a href="https://github.com/spring-projects/spring-retry">Spring Retry</a></p> |
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</li> |
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</ul> |
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</div> |
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</div> |
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</div> |
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</div> |
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<div class="sect1"> |
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<h2 id="_core_concepts"><a class="link" href="#_core_concepts">Core Concepts</a></h2> |
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<div class="sectionbody"> |
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<div class="paragraph"> |
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<p>To create a circuit breaker in your code, you can use the <code>CircuitBreakerFactory</code> API. When you include a Spring Cloud Circuit Breaker starter on your classpath, a bean that implements this API is automatically created for you. |
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The following example shows a simple example of how to use this API:</p> |
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</div> |
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<div class="exampleblock"> |
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<div class="content"> |
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<div class="listingblock"> |
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<div class="content"> |
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<pre class="highlightjs highlight"><code class="language-java hljs" data-lang="java">@Service |
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public static class DemoControllerService { |
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private RestTemplate rest; |
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private CircuitBreakerFactory cbFactory; |
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public DemoControllerService(RestTemplate rest, CircuitBreakerFactory cbFactory) { |
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this.rest = rest; |
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this.cbFactory = cbFactory; |
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} |
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public String slow() { |
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return cbFactory.create("slow").run(() -> rest.getForObject("/slow", String.class), throwable -> "fallback"); |
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} |
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}</code></pre> |
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</div> |
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</div> |
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</div> |
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</div> |
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<div class="paragraph"> |
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<p>The <code>CircuitBreakerFactory.create</code> API creates an instance of a class called <code>CircuitBreaker</code>. |
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The <code>run</code> method takes a <code>Supplier</code> and a <code>Function</code>. |
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The <code>Supplier</code> is the code that you are going to wrap in a circuit breaker. |
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The <code>Function</code> is the fallback that is executed if the circuit breaker is tripped. |
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The function is passed the <code>Throwable</code> that caused the fallback to be triggered. |
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You can optionally exclude the fallback if you do not want to provide one.</p> |
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</div> |
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<div class="sect2"> |
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<h3 id="_circuit_breakers_in_reactive_code"><a class="link" href="#_circuit_breakers_in_reactive_code">Circuit Breakers In Reactive Code</a></h3> |
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<div class="paragraph"> |
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<p>If Project Reactor is on the class path, you can also use <code>ReactiveCircuitBreakerFactory</code> for your reactive code. |
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The following example shows how to do so:</p> |
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</div> |
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<div class="exampleblock"> |
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<div class="content"> |
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<div class="listingblock"> |
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<div class="content"> |
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<pre class="highlightjs highlight"><code class="language-java hljs" data-lang="java">@Service |
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public static class DemoControllerService { |
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private ReactiveCircuitBreakerFactory cbFactory; |
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private WebClient webClient; |
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public DemoControllerService(WebClient webClient, ReactiveCircuitBreakerFactory cbFactory) { |
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this.webClient = webClient; |
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this.cbFactory = cbFactory; |
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} |
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public Mono<String> slow() { |
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return webClient.get().uri("/slow").retrieve().bodyToMono(String.class).transform( |
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it -> cbFactory.create("slow").run(it, throwable -> return Mono.just("fallback"))); |
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} |
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}</code></pre> |
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</div> |
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</div> |
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</div> |
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</div> |
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<div class="paragraph"> |
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<p>The <code>ReactiveCircuitBreakerFactory.create</code> API creates an instance of a class called <code>ReactiveCircuitBreaker</code>. |
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The <code>run</code> method takes a <code>Mono</code> or a <code>Flux</code> and wraps it in a circuit breaker. |
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You can optionally profile a fallback <code>Function</code>, which will be called if the circuit breaker is tripped and is passed the <code>Throwable</code> |
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that caused the failure.</p> |
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</div> |
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</div> |
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</div> |
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</div> |
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<div class="sect1"> |
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<h2 id="_configuration"><a class="link" href="#_configuration">Configuration</a></h2> |
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<div class="sectionbody"> |
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<div class="paragraph"> |
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<p>You can configure your circuit breakers by creating beans of type <code>Customizer</code>. |
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The <code>Customizer</code> interface has a single method (called <code>customize</code>) that takes the <code>Object</code> to customize.</p> |
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</div> |
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<div class="paragraph"> |
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<p>For detailed information on how to customize a given implementation see |
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the following documentation:</p> |
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</div> |
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<div class="ulist"> |
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<ul> |
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<li> |
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<p><a href="../../../../spring-cloud-circuitbreaker/current/reference/html/spring-cloud-circuitbreaker.html#configuring-resilience4j-circuit-breakers">Resilience4J</a></p> |
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</li> |
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<li> |
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<p><a href="https://github.com/alibaba/spring-cloud-alibaba/blob/master/spring-cloud-alibaba-docs/src/main/asciidoc/circuitbreaker-sentinel.adoc#circuit-breaker-spring-cloud-circuit-breaker-with-sentinel—​configuring-sentinel-circuit-breakers">Sentinal</a></p> |
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</li> |
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<li> |
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<p><a href="../../../../spring-cloud-circuitbreaker/current/reference/html/spring-cloud-circuitbreaker.html#configuring-spring-retry-circuit-breakers">Spring Retry</a></p> |
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</li> |
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</ul> |
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</div> |
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<div class="paragraph"> |
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<p>Some <code>CircuitBreaker</code> implementations such as <code>Resilience4JCircuitBreaker</code> call <code>customize</code> method every time <code>CircuitBreaker#run</code> is called. |
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It can be inefficient. In that case, you can use <code>CircuitBreaker#once</code> method. It is useful where calling <code>customize</code> many times doesn’t make sense, |
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for example, in case of <a href="https://resilience4j.readme.io/docs/circuitbreaker#section-consume-emitted-circuitbreakerevents">consuming Resilience4j’s events</a>.</p> |
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</div> |
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<div class="paragraph"> |
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<p>The following example shows the way for each <code>io.github.resilience4j.circuitbreaker.CircuitBreaker</code> to consume events.</p> |
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</div> |
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<div class="exampleblock"> |
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<div class="content"> |
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<div class="listingblock"> |
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<div class="content"> |
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<pre class="highlightjs highlight"><code class="language-java hljs" data-lang="java">Customizer.once(circuitBreaker -> { |
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circuitBreaker.getEventPublisher() |
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.onStateTransition(event -> log.info("{}: {}", event.getCircuitBreakerName(), event.getStateTransition())); |
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}, CircuitBreaker::getName)</code></pre> |
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</div> |
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