192 lines
8.3 KiB
HTML
192 lines
8.3 KiB
HTML
<!DOCTYPE html>
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<title>Spring Cloud Bus</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="#_spring_cloud_bus">Spring Cloud Bus</a>
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<ul class="sectlevel2">
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<li><a href="#_configuration_management_with_spring_cloud_config_and_spring_cloud_bus">Configuration Management with Spring Cloud Config and Spring Cloud Bus</a></li>
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</ul>
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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 id="content">
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<div class="sect1">
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<h2 id="_spring_cloud_bus"><a class="link" href="#_spring_cloud_bus">Spring Cloud Bus</a></h2>
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<div class="sectionbody">
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<div class="paragraph">
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<p>Using <a href="https://cloud.google.com/pubsub/">Cloud Pub/Sub</a> as the <a href="https://spring.io/projects/spring-cloud-bus">Spring Cloud Bus</a> implementation is as simple as importing the <code>spring-cloud-gcp-starter-bus-pubsub</code> starter.</p>
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</div>
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<div class="paragraph">
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<p>This starter brings in the <a href="spring-stream.html#_spring_cloud_stream">Spring Cloud Stream binder for Cloud Pub/Sub</a>, which is used to both publish and subscribe to the bus.
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If the bus topic (named <code>springCloudBus</code> by default) does not exist, the binder automatically creates it.
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The binder also creates anonymous subscriptions for each project using the <code>spring-cloud-gcp-starter-bus-pubsub</code> starter.</p>
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</div>
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<div class="paragraph">
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<p>Maven coordinates, using <a href="getting-started.html#_bill_of_materials">Spring Cloud GCP BOM</a>:</p>
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</div>
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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-xml hljs" data-lang="xml"><dependency>
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<groupId>org.springframework.cloud</groupId>
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<artifactId>spring-cloud-gcp-starter-bus-pubsub</artifactId>
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</dependency></code></pre>
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</div>
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</div>
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<div class="paragraph">
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<p>Gradle coordinates:</p>
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</div>
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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-groovy hljs" data-lang="groovy">dependencies {
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compile group: 'org.springframework.cloud', name: 'spring-cloud-gcp-starter-bus-pubsub'
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}</code></pre>
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</div>
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</div>
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<div class="sect2">
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<h3 id="_configuration_management_with_spring_cloud_config_and_spring_cloud_bus"><a class="link" href="#_configuration_management_with_spring_cloud_config_and_spring_cloud_bus">Configuration Management with Spring Cloud Config and Spring Cloud Bus</a></h3>
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<div class="paragraph">
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<p>Spring Cloud Bus can be used to push configuration changes from a Spring Cloud Config server to the clients listening on the same bus.</p>
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</div>
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<div class="paragraph">
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<p>To use GCP Pub/Sub as the bus implementation, both the configuration server and the configuration client need the <code>spring-cloud-gcp-starter-bus-pubsub</code> dependency.</p>
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</div>
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<div class="paragraph">
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<p>All other configuration is standard to <a href="https://spring.io/projects/spring-cloud-config">Spring Cloud Config</a>.</p>
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</div>
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<div class="imageblock">
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<div class="content">
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<img src="./images/spring_cloud_bus_over_pubsub.png" alt="spring cloud bus over pubsub">
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</div>
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</div>
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<div class="paragraph">
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<p>Spring Cloud Config Server typically runs on port <code>8888</code>, and can read configuration from a <a href="https://cloud.spring.io/spring-cloud-config/spring-cloud-config.html#_environment_repository">variety of source control systems</a> such as GitHub, and even from the local filesystem.
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When the server is notified that new configuration is available, it fetches the updated configuration and sends a notification (<code>RefreshRemoteApplicationEvent</code>) out via Spring Cloud Bus.</p>
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</div>
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<div class="paragraph">
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<p>When configuration is stored locally, config server polls the parent directory for changes.
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With configuration stored in source control repository, such as GitHub, the config server needs to be notified that a new version of configuration is available.
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In a deployed server, this would be done automatically through a GitHub webhook, but in a local testing scenario, the <code>/monitor</code> HTTP endpoint needs to be invoked manually.</p>
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</div>
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<div class="listingblock">
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<div class="content">
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<pre>curl -X POST http://localhost:8888/monitor -H "X-Github-Event: push" -H "Content-Type: application/json" -d '{"commits": [{"modified": ["application.properties"]}]}'</pre>
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</div>
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</div>
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<div class="paragraph">
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<p>By adding the <code>spring-cloud-gcp-starter-bus-pubsub</code> dependency, you instruct Spring Cloud Bus to use Cloud Pub/Sub to broadcast configuration changes.
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Spring Cloud Bus will then create a topic named <code>springCloudBus</code>, as well as a subscription for each configuration client.</p>
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</div>
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<div class="paragraph">
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<p>The configuration server happens to also be a configuration client, subscribing to the configuration changes that it sends out.
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Thus, in a scenario with one configuration server and one configuration client, two anonymous subscriptions to the <code>springCloudBus</code> topic are created.
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However, a config server disables configuration refresh by default (see <a href="https://static.javadoc.io/org.springframework.cloud/spring-cloud-config-server/2.1.0.RELEASE/index.html">ConfigServerBootstrapApplicationListener</a> for more details).</p>
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</div>
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<div class="paragraph">
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<p>A <a href="https://github.com/spring-cloud/spring-cloud-gcp/tree/master/spring-cloud-gcp-samples/spring-cloud-gcp-pubsub-bus-config-sample">demo application</a> showing configuration management and distribution over a Cloud Pub/Sub-powered bus is available.
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The sample contains two examples of configuration management with Spring Cloud Bus: one monitoring a local file system, and the other retrieving configuration from a GitHub repository.</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>
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