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<title>1. Spring Cloud Context: Application Context Services</title><link rel="stylesheet" type="text/css" href="css/manual-multipage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="multi_spring-cloud-commons.html" title="Cloud Native Applications"><link rel="up" href="multi_spring-cloud-commons.html" title="Cloud Native Applications"><link rel="prev" href="multi_pr01.html" title=""><link rel="next" href="multi__spring_cloud_commons_common_abstractions.html" title="2. Spring Cloud Commons: Common Abstractions"></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">1. Spring Cloud Context: Application Context Services</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi_pr01.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="multi__spring_cloud_commons_common_abstractions.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_spring_cloud_context_application_context_services" href="#_spring_cloud_context_application_context_services"></a>1. Spring Cloud Context: Application Context Services</h1></div></div></div><p>Spring Boot has an opinionated view of how to build an application with Spring. |
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For instance, it has conventional locations for common configuration files and has endpoints for common management and monitoring tasks. |
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Spring Cloud builds on top of that and adds a few features that probably all components in a system would use or occasionally need.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_the_bootstrap_application_context" href="#_the_bootstrap_application_context"></a>1.1 The Bootstrap Application Context</h2></div></div></div><p>A Spring Cloud application operates by creating a “bootstrap” context, which is a parent context for the main application. |
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It is responsible for loading configuration properties from the external sources and for decrypting properties in the local external configuration files. |
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The two contexts share an <code class="literal">Environment</code>, which is the source of external properties for any Spring application. |
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By default, bootstrap properties (not <code class="literal">bootstrap.properties</code> but properties that are loaded during the bootstrap phase) are added with high precedence, so they cannot be overridden by local configuration.</p><p>The bootstrap context uses a different convention for locating external configuration than the main application context. |
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Instead of <code class="literal">application.yml</code> (or <code class="literal">.properties</code>), you can use <code class="literal">bootstrap.yml</code>, keeping the external configuration for bootstrap and main context |
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nicely separate. |
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The following listing shows an example:</p><p><b>bootstrap.yml. </b> |
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</p><pre class="screen">spring: |
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application: |
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name: foo |
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cloud: |
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config: |
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uri: ${SPRING_CONFIG_URI:http://localhost:8888}</pre><p> |
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</p><p>If your application needs any application-specific configuration from the server, it is a good idea to set the <code class="literal">spring.application.name</code> (in <code class="literal">bootstrap.yml</code> or <code class="literal">application.yml</code>).</p><p>You can disable the bootstrap process completely by setting <code class="literal">spring.cloud.bootstrap.enabled=false</code> (for example, in system properties).</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_application_context_hierarchies" href="#_application_context_hierarchies"></a>1.2 Application Context Hierarchies</h2></div></div></div><p>If you build an application context from <code class="literal">SpringApplication</code> or <code class="literal">SpringApplicationBuilder</code>, then the Bootstrap context is added as a parent to that context. |
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It is a feature of Spring that child contexts inherit property sources and profiles from their parent, so the “main” application context contains additional property sources, compared to building the same context without Spring Cloud Config. |
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The additional property sources are:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">“bootstrap”: If any <code class="literal">PropertySourceLocators</code> are found in the Bootstrap context and if they have non-empty properties, an optional <code class="literal">CompositePropertySource</code> appears with high priority. |
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An example would be properties from the Spring Cloud Config Server. |
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See “<a class="xref" href="multi__spring_cloud_context_application_context_services.html#customizing-bootstrap-property-sources" title="1.6 Customizing the Bootstrap Property Sources">Section 1.6, “Customizing the Bootstrap Property Sources”</a>” for instructions on how to customize the contents of this property source.</li><li class="listitem">“applicationConfig: [classpath:bootstrap.yml]” (and related files if Spring profiles are active): If you have a <code class="literal">bootstrap.yml</code> (or <code class="literal">.properties</code>), those properties are used to configure the Bootstrap context. |
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Then they get added to the child context when its parent is set. |
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They have lower precedence than the <code class="literal">application.yml</code> (or <code class="literal">.properties</code>) and any other property sources that are added to the child as a normal part of the process of creating a Spring Boot application. |
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See “<a class="xref" href="multi__spring_cloud_context_application_context_services.html#customizing-bootstrap-properties" title="1.3 Changing the Location of Bootstrap Properties">Section 1.3, “Changing the Location of Bootstrap Properties”</a>” for instructions on how to customize the contents of these property sources.</li></ul></div><p>Because of the ordering rules of property sources, the “bootstrap” entries take precedence. |
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However, note that these do not contain any data from <code class="literal">bootstrap.yml</code>, which has very low precedence but can be used to set defaults.</p><p>You can extend the context hierarchy by setting the parent context of any <code class="literal">ApplicationContext</code> you create — for example, by using its own interface or with the <code class="literal">SpringApplicationBuilder</code> convenience methods (<code class="literal">parent()</code>, <code class="literal">child()</code> and <code class="literal">sibling()</code>). |
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The bootstrap context is the parent of the most senior ancestor that you create yourself. |
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Every context in the hierarchy has its own “bootstrap” (possibly empty) property source to avoid promoting values inadvertently from parents down to their descendants. |
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If there is a Config Server, every context in the hierarchy can also (in principle) have a different <code class="literal">spring.application.name</code> and, hence, a different remote property source. |
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Normal Spring application context behavior rules apply to property resolution: properties from a child context override those in |
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the parent, by name and also by property source name. |
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(If the child has a property source with the same name as the parent, the value from the parent is not included in the child).</p><p>Note that the <code class="literal">SpringApplicationBuilder</code> lets you share an <code class="literal">Environment</code> amongst the whole hierarchy, but that is not the default. |
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Thus, sibling contexts, in particular, do not need to have the same profiles or property sources, even though they may share common values with their parent.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="customizing-bootstrap-properties" href="#customizing-bootstrap-properties"></a>1.3 Changing the Location of Bootstrap Properties</h2></div></div></div><p>The <code class="literal">bootstrap.yml</code> (or <code class="literal">.properties</code>) location can be specified by setting <code class="literal">spring.cloud.bootstrap.name</code> (default: <code class="literal">bootstrap</code>) or <code class="literal">spring.cloud.bootstrap.location</code> (default: empty) — for example, in System properties. |
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Those properties behave like the <code class="literal">spring.config.*</code> variants with the same name. |
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In fact, they are used to set up the bootstrap <code class="literal">ApplicationContext</code> by setting those properties in its <code class="literal">Environment</code>. |
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If there is an active profile (from <code class="literal">spring.profiles.active</code> or through the <code class="literal">Environment</code> API in the |
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context you are building), properties in that profile get loaded as well, the same as in a regular Spring Boot app — for example, from <code class="literal">bootstrap-development.properties</code> for a <code class="literal">development</code> profile.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="overriding-bootstrap-properties" href="#overriding-bootstrap-properties"></a>1.4 Overriding the Values of Remote Properties</h2></div></div></div><p>The property sources that are added to your application by the bootstrap context are often “remote” (from example, from Spring Cloud Config Server). |
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By default, they cannot be overridden locally. |
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If you want to let your applications override the remote properties with their own System properties or config files, the remote property source has to grant it permission by setting <code class="literal">spring.cloud.config.allowOverride=true</code> (it does not work to set this locally). |
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Once that flag is set, two finer-grained settings control the location of the remote properties in relation to system properties and the application’s local configuration:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="literal">spring.cloud.config.overrideNone=true</code>: Override from any local property source.</li><li class="listitem"><code class="literal">spring.cloud.config.overrideSystemProperties=false</code>: Only system properties, command line arguments, and environment variables (but not the local config files) should override the remote settings.</li></ul></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_customizing_the_bootstrap_configuration" href="#_customizing_the_bootstrap_configuration"></a>1.5 Customizing the Bootstrap Configuration</h2></div></div></div><p>The bootstrap context can be set to do anything you like by adding entries to <code class="literal">/META-INF/spring.factories</code> under a key named <code class="literal">org.springframework.cloud.bootstrap.BootstrapConfiguration</code>. |
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This holds a comma-separated list of Spring <code class="literal">@Configuration</code> classes that are used to create the context. |
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Any beans that you want to be available to the main application context for autowiring can be created here. |
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There is a special contract for <code class="literal">@Beans</code> of type <code class="literal">ApplicationContextInitializer</code>. |
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If you want to control the startup sequence, classes can be marked with an <code class="literal">@Order</code> annotation (the default order is <code class="literal">last</code>).</p><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Warning"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="images/warning.png"></td><th align="left">Warning</th></tr><tr><td align="left" valign="top"><p>When adding custom <code class="literal">BootstrapConfiguration</code>, be careful that the classes you add are not <code class="literal">@ComponentScanned</code> by mistake into your “main” application context, where they might not be needed. |
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Use a separate package name for boot configuration classes and make sure that name is not already covered by your <code class="literal">@ComponentScan</code> or <code class="literal">@SpringBootApplication</code> annotated configuration classes.</p></td></tr></table></div><p>The bootstrap process ends by injecting initializers into the main <code class="literal">SpringApplication</code> instance (which is the normal Spring Boot startup sequence, whether it is running as a standalone application or deployed in an application server). |
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First, a bootstrap context is created from the classes found in <code class="literal">spring.factories</code>. |
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Then, all <code class="literal">@Beans</code> of type <code class="literal">ApplicationContextInitializer</code> are added to the main <code class="literal">SpringApplication</code> before it is started.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="customizing-bootstrap-property-sources" href="#customizing-bootstrap-property-sources"></a>1.6 Customizing the Bootstrap Property Sources</h2></div></div></div><p>The default property source for external configuration added by the bootstrap process is the Spring Cloud Config Server, but you can add additional sources by adding beans of type <code class="literal">PropertySourceLocator</code> to the bootstrap context (through <code class="literal">spring.factories</code>). |
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For instance, you can insert additional properties from a different server or from a database.</p><p>As an example, consider the following custom locator:</p><pre class="programlisting"><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-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> CustomPropertySourceLocator <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">implements</span> PropertySourceLocator { |
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|
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<em><span class="hl-annotation" style="color: gray">@Override</span></em> |
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> PropertySource<?> locate(Environment environment) { |
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> MapPropertySource(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"customProperty"</span>, |
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Collections.<String, Object>singletonMap(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"property.from.sample.custom.source"</span>, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"worked as intended"</span>)); |
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} |
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|
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}</pre><p>The <code class="literal">Environment</code> that is passed in is the one for the <code class="literal">ApplicationContext</code> about to be created — in other words, the one for which we supply additional property sources for. |
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It already has its normal Spring Boot-provided property sources, so you can use those to locate a property source specific to this <code class="literal">Environment</code> (for example, by keying it on <code class="literal">spring.application.name</code>, as is done in the default Spring Cloud Config Server property source locator).</p><p>If you create a jar with this class in it and then add a <code class="literal">META-INF/spring.factories</code> containing the following, the <code class="literal">customProperty</code> <code class="literal">PropertySource</code> appears in any application that includes that jar on its classpath:</p><pre class="screen">org.springframework.cloud.bootstrap.BootstrapConfiguration=sample.custom.CustomPropertySourceLocator</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_logging_configuration" href="#_logging_configuration"></a>1.7 Logging Configuration</h2></div></div></div><p>If you are going to use Spring Boot to configure log settings than |
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you should place this configuration in `bootstrap.[yml | properties] |
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if you would like it to apply to all events.</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>For Spring Cloud to initialize logging configuration properly you cannot use a custom prefix. For example, |
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using <code class="literal">custom.loggin.logpath</code> will not be recognized by Spring Cloud when initializing the logging system.</p></td></tr></table></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_environment_changes" href="#_environment_changes"></a>1.8 Environment Changes</h2></div></div></div><p>The application listens for an <code class="literal">EnvironmentChangeEvent</code> and reacts to the change in a couple of standard ways (additional <code class="literal">ApplicationListeners</code> can be added as <code class="literal">@Beans</code> by the user in the normal way). |
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When an <code class="literal">EnvironmentChangeEvent</code> is observed, it has a list of key values that have changed, and the application uses those to:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">Re-bind any <code class="literal">@ConfigurationProperties</code> beans in the context</li><li class="listitem">Set the logger levels for any properties in <code class="literal">logging.level.*</code></li></ul></div><p>Note that the Config Client does not, by default, poll for changes in the <code class="literal">Environment</code>. |
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Generally, we would not recommend that approach for detecting changes (although you could set it up with a |
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<code class="literal">@Scheduled</code> annotation). |
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If you have a scaled-out client application, it is better to broadcast the <code class="literal">EnvironmentChangeEvent</code> to all the instances instead of having them polling for changes (for example, by using the <a class="link" href="https://github.com/spring-cloud/spring-cloud-bus" target="_top">Spring Cloud Bus</a>).</p><p>The <code class="literal">EnvironmentChangeEvent</code> covers a large class of refresh use cases, as long as you can actually make a change to the <code class="literal">Environment</code> and publish the event. |
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Note that those APIs are public and part of core Spring). |
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You can verify that the changes are bound to <code class="literal">@ConfigurationProperties</code> beans by visiting the <code class="literal">/configprops</code> endpoint (a normal Spring Boot Actuator feature). |
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For instance, a <code class="literal">DataSource</code> can have its <code class="literal">maxPoolSize</code> changed at runtime (the default <code class="literal">DataSource</code> created by Spring Boot is an <code class="literal">@ConfigurationProperties</code> bean) and grow capacity dynamically. |
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Re-binding <code class="literal">@ConfigurationProperties</code> does not cover another large class of use cases, where you need more control over the refresh and where you need a change to be atomic over the whole <code class="literal">ApplicationContext</code>. |
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To address those concerns, we have <code class="literal">@RefreshScope</code>.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="refresh-scope" href="#refresh-scope"></a>1.9 Refresh Scope</h2></div></div></div><p>When there is a configuration change, a Spring <code class="literal">@Bean</code> that is marked as <code class="literal">@RefreshScope</code> gets special treatment. |
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This feature addresses the problem of stateful beans that only get their configuration injected when they are initialized. |
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For instance, if a <code class="literal">DataSource</code> has open connections when the database URL is changed via the <code class="literal">Environment</code>, you probably want the holders of those connections to be able to complete what they are doing. |
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Then, the next time something borrows a connection from the pool, it gets one with the new URL.</p><p>Sometimes, it might even be mandatory to apply the <code class="literal">@RefreshScope</code> |
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annotation on some beans which can be only initialized once. If a bean |
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is "immutable", you will have to either annotate the bean with <code class="literal">@RefreshScope</code> |
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or specify the classname under the property key |
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<code class="literal">spring.cloud.refresh.extra-refreshable</code>.</p><p>Refresh scope beans are lazy proxies that initialize when they are used (that is, when a method is called), and the scope acts as a cache of initialized values. |
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To force a bean to re-initialize on the next method call, you must invalidate its cache entry.</p><p>The <code class="literal">RefreshScope</code> is a bean in the context and has a public <code class="literal">refreshAll()</code> method to refresh all beans in the scope by clearing the target cache. |
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The <code class="literal">/refresh</code> endpoint exposes this functionality (over HTTP or JMX). |
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To refresh an individual bean by name, there is also a <code class="literal">refresh(String)</code> method.</p><p>To expose the <code class="literal">/refresh</code> endpoint, you need to add following configuration to your application:</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute">management</span>: |
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> endpoints</span>: |
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> web</span>: |
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> exposure</span>: |
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> include</span>: refresh</pre><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><code class="literal">@RefreshScope</code> works (technically) on an <code class="literal">@Configuration</code> class, but it might lead to surprising behavior. |
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For example, it does not mean that all the <code class="literal">@Beans</code> defined in that class are themselves in <code class="literal">@RefreshScope</code>. |
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Specifically, anything that depends on those beans cannot rely on them being updated when a refresh is initiated, unless it is itself in <code class="literal">@RefreshScope</code>. |
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In that case, it is rebuilt on a refresh and its dependencies are re-injected. At that point, they are re-initialized from the refreshed <code class="literal">@Configuration</code>).</p></td></tr></table></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_encryption_and_decryption" href="#_encryption_and_decryption"></a>1.10 Encryption and Decryption</h2></div></div></div><p>Spring Cloud has an <code class="literal">Environment</code> pre-processor for decrypting property values locally. |
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It follows the same rules as the Config Server and has the same external configuration through <code class="literal">encrypt.*</code>. |
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Thus, you can use encrypted values in the form of <code class="literal">{cipher}*</code> and, as long as there is a valid key, they are decrypted before the main application context gets the <code class="literal">Environment</code> settings. |
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To use the encryption features in an application, you need to include Spring Security RSA in your classpath (Maven co-ordinates: "org.springframework.security:spring-security-rsa"), and you also need the full strength JCE extensions in your JVM.</p><p>If you get an exception due to "Illegal key size" and you use Sun’s JDK, you need to install the Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files. |
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See the following links for more information:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><a class="link" href="http://www.oracle.com/technetwork/java/javase/downloads/jce-6-download-429243.html" target="_top">Java 6 JCE</a></li><li class="listitem"><a class="link" href="http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html" target="_top">Java 7 JCE</a></li><li class="listitem"><a class="link" href="http://www.oracle.com/technetwork/java/javase/downloads/jce8-download-2133166.html" target="_top">Java 8 JCE</a></li></ul></div><p>Extract the files into the JDK/jre/lib/security folder for whichever version of JRE/JDK x64/x86 you use.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_endpoints" href="#_endpoints"></a>1.11 Endpoints</h2></div></div></div><p>For a Spring Boot Actuator application, some additional management endpoints are available. You can use:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="literal">POST</code> to <code class="literal">/actuator/env</code> to update the <code class="literal">Environment</code> and rebind <code class="literal">@ConfigurationProperties</code> and log levels.</li><li class="listitem"><code class="literal">/actuator/refresh</code> to re-load the boot strap context and refresh the <code class="literal">@RefreshScope</code> beans.</li><li class="listitem"><code class="literal">/actuator/restart</code> to close the <code class="literal">ApplicationContext</code> and restart it (disabled by default).</li><li class="listitem"><code class="literal">/actuator/pause</code> and <code class="literal">/actuator/resume</code> for calling the <code class="literal">Lifecycle</code> methods (<code class="literal">stop()</code> and <code class="literal">start()</code> on the <code class="literal">ApplicationContext</code>).</li></ul></div><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>If you disable the <code class="literal">/actuator/restart</code> endpoint then the <code class="literal">/actuator/pause</code> and <code class="literal">/actuator/resume</code> endpoints |
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will also be disabled since they are just a special case of <code class="literal">/actuator/restart</code>.</p></td></tr></table></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi_pr01.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="multi__spring_cloud_commons_common_abstractions.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"> </td><td width="20%" align="center"><a accesskey="h" href="multi_spring-cloud-commons.html">Home</a></td><td width="40%" align="right" valign="top"> 2. Spring Cloud Commons: Common Abstractions</td></tr></table></div></body></html> |