<title>Cloud Native Applications</title><linkrel="stylesheet"type="text/css"href="css/manual-singlepage.css"><metaname="generator"content="DocBook XSL Stylesheets V1.78.1"></head><bodybgcolor="white"text="black"link="#0000FF"vlink="#840084"alink="#0000FF"><divlang="en"class="book"><divclass="titlepage"><div><div><h1class="title"><aname="d0e3"></a>Cloud Native Applications</h1></div></div><hr></div><divclass="toc"><p><b>Table of Contents</b></p><dlclass="toc"><dt><spanclass="preface"><ahref="#d0e9"></a></span></dt><dt><spanclass="chapter"><ahref="#_spring_cloud_context_application_context_services">1. Spring Cloud Context: Application Context Services</a></span></dt><dd><dl><dt><spanclass="section"><ahref="#_the_bootstrap_application_context">1.1. The Bootstrap Application Context</a></span></dt><dt><spanclass="section"><ahref="#_application_context_hierarchies">1.2. Application Context Hierarchies</a></span></dt><dt><spanclass="section"><ahref="#customizing-bootstrap-properties">1.3. Changing the Location of Bootstrap Properties</a></span></dt><dt><spanclass="section"><ahref="#overriding-bootstrap-properties">1.4. Overriding the Values of Remote Properties</a></span></dt><dt><spanclass="section"><ahref="#_customizing_the_bootstrap_configuration">1.5. Customizing the Bootstrap Configuration</a></span></dt><dt><spanclass="section"><ahref="#customizing-bootstrap-property-sources">1.6. Customizing the Bootstrap Property Sources</a></span></dt><dt><spanclass="section"><ahref="#_environment_changes">1.7. Environment Changes</a></span></dt><dt><spanclass="section"><ahref="#_refresh_scope">1.8. Refresh Scope</a></span></dt><dt><spanclass="section"><ahref="#_encryption_and_decryption">1.9. Encryption and Decryption</a></span></dt><dt><spanclass="section"><ahref="#_endpoints">1.10. Endpoints</a></span></dt></dl></dd><dt><spanclass="chapter"><ahref="#_spring_cloud_commons_common_abstractions">2. Spring Cloud Commons: Common Abstractions</a></span></dt><dd><dl><dt><spanclass="section"><ahref="#__enablediscoveryclient">2.1. @EnableDiscoveryClient</a></span></dt><dd><dl><dt><spanclass="section"><ahref="#_health_indicator">2.1.1. Health Indicator</a></span></dt></dl></dd><dt><spanclass="section"><ahref="#_serviceregistry">2.2. ServiceRegistry</a></span></dt><dd><dl><dt><spanclass="section"><ahref="#_serviceregistry_auto_registration">2.2.1. ServiceRegistry Auto-Registration</a></span></dt><dt><spanclass="section"><ahref="#_service_registry_actuator_endpoint">2.2.2. Service Registry Actuator Endpoint</a></span></dt></dl></dd><dt><spanclass="section"><ahref="#_spring_resttemplate_as_a_load_balancer_client">2.3. Spring RestTemplate as a Load Balancer Client</a></span></dt><dt><spanclass="section"><ahref="#_spring_webclient_as_a_load_balancer_client">2.4. Spring WebClient as a Load Balancer Client</a></span></dt><dd><dl><dt><spanclass="section"><ahref="#_retrying_failed_requests">2.4.1. Retrying Failed Requests</a></span></dt></dl></dd><dt><spanclass="section"><ahref="#_multiple_resttemplate_objects">2.5. Multiple RestTemplate objects</a></span></dt><dt><spanclass="section"><ahref="#loadbalanced-webclient">2.6. Spring WebFlux WebClient as a Load Balancer Client</a></span></dt><dt><spanclass="section"><ahref="#ignore-network-interfaces">2.7. Ignore Network Interfaces</a></span></dt><dt><spanclass="section"><ahref="#http-clients">2.8. HTTP Client Factories</a></span></dt><dt><spanclass="section"><ahref="#enabled-features">2.9. Enabled Features</a></span></dt><dd><dl><dt><spanclass="section"><ahref="#_feature_types">2.9.1. Feature types</a></span></dt><dt><spanclass="section"><ahref="#_declaring_features">2.9.2. Declaring features</a></span></dt></dl></dd></dl></dd></dl></div><divclass="preface"><divclass="titlepage"><div><div><h1class="title"><aname="d0e9"href="#d0e9"></a></h1></div></div></div><p><aclass="link"href="http://pivotal.io/platform-as-a-service/migrating-to-cloud-native-application-architectures-ebook"target="_top">Cloud Native</a> is a style of
A related discipline is that of building <aclass="link"href="http://12factor.net/"target="_top">12-factor Applications</a>, in which development practices are aligned with delivery and operations goals — for instance, by using declarative programming and management and monitoring.
Spring Cloud facilitates these styles of development in a number of specific ways.
The starting point is a set of features to which all components in a distributed system need easy access.</p><p>Many of those features are covered by <aclass="link"href="http://projects.spring.io/spring-boot"target="_top">Spring Boot</a>, on which Spring Cloud builds. Some more features are delivered by Spring Cloud as two libraries: Spring Cloud Context and Spring Cloud Commons.
Spring Cloud Context provides utilities and special services for the <codeclass="literal">ApplicationContext</code> of a Spring Cloud application (bootstrap context, encryption, refresh scope, and environment endpoints). Spring Cloud Commons is a set of abstractions and common classes used in different Spring Cloud implementations (such as Spring Cloud Netflix and Spring Cloud Consul).</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.
See the following links for more information:</p><divclass="itemizedlist"><ulclass="itemizedlist"style="list-style-type: disc; "><liclass="listitem"><aclass="link"href="http://www.oracle.com/technetwork/java/javase/downloads/jce-6-download-429243.html"target="_top">Java 6 JCE</a></li><liclass="listitem"><aclass="link"href="http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html"target="_top">Java 7 JCE</a></li><liclass="listitem"><aclass="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><divclass="note"style="margin-left: 0.5in; margin-right: 0.5in;"><tableborder="0"summary="Note"><tr><tdrowspan="2"align="center"valign="top"width="25"><imgalt="[Note]"src="images/note.png"></td><thalign="left">Note</th></tr><tr><tdalign="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, you can find the source code and issue trackers for the project at <aclass="link"href="https://github.com/spring-cloud/spring-cloud-commons/tree/master/docs/src/main/asciidoc"target="_top">github</a>.</p></td></tr></table></div></div><divclass="chapter"><divclass="titlepage"><div><div><h1class="title"><aname="_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.
For instance, it has conventional locations for common configuration files and has endpoints for common management and monitoring tasks.
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><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="_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.
It is responsible for loading configuration properties from the external sources and for decrypting properties in the local external configuration files.
The two contexts share an <codeclass="literal">Environment</code>, which is the source of external properties for any Spring application.
By default, bootstrap properties 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.
Instead of <codeclass="literal">application.yml</code> (or <codeclass="literal">.properties</code>), you can use <codeclass="literal">bootstrap.yml</code>, keeping the external configuration for bootstrap and main context
nicely separate.
The following listing shows an example:</p><p><b>bootstrap.yml. </b>
</p><p>If your application needs any application-specific configuration from the server, it is a good idea to set the <codeclass="literal">spring.application.name</code> (in <codeclass="literal">bootstrap.yml</code> or <codeclass="literal">application.yml</code>).</p><p>You can disable the bootstrap process completely by setting <codeclass="literal">spring.cloud.bootstrap.enabled=false</code> (for example, in system properties).</p></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="_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 <codeclass="literal">SpringApplication</code> or <codeclass="literal">SpringApplicationBuilder</code>, then the Bootstrap context is added as a parent to that context.
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.
The additional property sources are:</p><divclass="itemizedlist"><ulclass="itemizedlist"style="list-style-type: disc; "><liclass="listitem">“bootstrap”: If any <codeclass="literal">PropertySourceLocators</code> are found in the Bootstrap context and if they have non-empty properties, an optional <codeclass="literal">CompositePropertySource</code> appears with high priority.
An example would be properties from the Spring Cloud Config Server.
See “<aclass="xref"href="#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><liclass="listitem">“applicationConfig: [classpath:bootstrap.yml]” (and related files if Spring profiles are active): If you have a <codeclass="literal">bootstrap.yml</code> (or <codeclass="literal">.properties</code>), those properties are used to configure the Bootstrap context.
Then they get added to the child context when its parent is set.
They have lower precedence than the <codeclass="literal">application.yml</code> (or <codeclass="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.
See “<aclass="xref"href="#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.
However, note that these do not contain any data from <codeclass="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 <codeclass="literal">ApplicationContext</code> you create — for example, by using its own interface or with the <codeclass="literal">SpringApplicationBuilder</code> convenience methods (<codeclass="literal">parent()</code>, <codeclass="literal">child()</code> and <codeclass="literal">sibling()</code>).
The bootstrap context is the parent of the most senior ancestor that you create yourself.
Every context in the hierarchy has its own “bootstrap” (possibly empty) property source to avoid promoting values inadvertently from parents down to their descendants.
If there is a Config Server, every context in the hierarchy can also (in principle) have a different <codeclass="literal">spring.application.name</code> and, hence, a different remote property source.
Normal Spring application context behavior rules apply to property resolution: properties from a child context override those in
the parent, by name and also by property source name.
(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 <codeclass="literal">SpringApplicationBuilder</code> lets you share an <codeclass="literal">Environment</code> amongst the whole hierarchy, but that is not the default.
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><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="customizing-bootstrap-properties"href="#customizing-bootstrap-properties"></a>1.3 Changing the Location of Bootstrap Properties</h2></div></div></div><p>The <codeclass="literal">bootstrap.yml</code> (or <codeclass="literal">.properties</code>) location can be specified by setting <codeclass="literal">spring.cloud.bootstrap.name</code> (default: <codeclass="literal">bootstrap</code>) or <codeclass="literal">spring.cloud.bootstrap.location</code> (default: empty) — for example, in System properties.
Those properties behave like the <codeclass="literal">spring.config.*</code> variants with the same name.
In fact, they are used to set up the bootstrap <codeclass="literal">ApplicationContext</code> by setting those properties in its <codeclass="literal">Environment</code>.
If there is an active profile (from <codeclass="literal">spring.profiles.active</code> or through the <codeclass="literal">Environment</code> API in the
context you are building), properties in that profile get loaded as well, the same as in a regular Spring Boot app — for example, from <codeclass="literal">bootstrap-development.properties</code> for a <codeclass="literal">development</code> profile.</p></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="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).
By default, they cannot be overridden locally, except on the command line.
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 <codeclass="literal">spring.cloud.config.allowOverride=true</code> (it does not work to set this locally).
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><divclass="itemizedlist"><ulclass="itemizedlist"style="list-style-type: disc; "><liclass="listitem"><codeclass="literal">spring.cloud.config.overrideNone=true</code>: Override from any local property source.</li><liclass="listitem"><codeclass="literal">spring.cloud.config.overrideSystemProperties=false</code>: Only system properties and environment variables (but not the local config files) should override the remote settings.</li></ul></div></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="_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 <codeclass="literal">/META-INF/spring.factories</code> under a key named <codeclass="literal">org.springframework.cloud.bootstrap.BootstrapConfiguration</code>.
This holds a comma-separated list of Spring <codeclass="literal">@Configuration</code> classes that are used to create the context.
Any beans that you want to be available to the main application context for autowiring can be created here.
There is a special contract for <codeclass="literal">@Beans</code> of type <codeclass="literal">ApplicationContextInitializer</code>.
If you want to control the startup sequence, classes can be marked with an <codeclass="literal">@Order</code> annotation (the default order is <codeclass="literal">last</code>).</p><divclass="warning"style="margin-left: 0.5in; margin-right: 0.5in;"><tableborder="0"summary="Warning"><tr><tdrowspan="2"align="center"valign="top"width="25"><imgalt="[Warning]"src="images/warning.png"></td><thalign="left">Warning</th></tr><tr><tdalign="left"valign="top"><p>When adding custom <codeclass="literal">BootstrapConfiguration</code>, be careful that the classes you add are not <codeclass="literal">@ComponentScanned</code> by mistake into your “main” application context, where they might not be needed.
Use a separate package name for boot configuration classes and make sure that name is not already covered by your <codeclass="literal">@ComponentScan</code> or <codeclass="literal">@SpringBootApplication</code> annotated configuration classes.</p></td></tr></table></div><p>The bootstrap process ends by injecting initializers into the main <codeclass="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).
First, a bootstrap context is created from the classes found in <codeclass="literal">spring.factories</code>.
Then, all <codeclass="literal">@Beans</code> of type <codeclass="literal">ApplicationContextInitializer</code> are added to the main <codeclass="literal">SpringApplication</code> before it is started.</p></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="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 <codeclass="literal">PropertySourceLocator</code> to the bootstrap context (through <codeclass="literal">spring.factories</code>).
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><preclass="programlisting"><em><spanclass="hl-annotation"style="color: gray">@Configuration</span></em>
Collections.<String, Object>singletonMap(<spanxmlns:d="http://docbook.org/ns/docbook"class="hl-string">"property.from.sample.custom.source"</span>, <spanxmlns:d="http://docbook.org/ns/docbook"class="hl-string">"worked as intended"</span>));
}</pre><p>The <codeclass="literal">Environment</code> that is passed in is the one for the <codeclass="literal">ApplicationContext</code> about to be created — in other words, the one for which we supply additional property sources for.
It already has its normal Spring Boot-provided property sources, so you can use those to locate a property source specific to this <codeclass="literal">Environment</code> (for example, by keying it on <codeclass="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 <codeclass="literal">META-INF/spring.factories</code> containing the following, the <codeclass="literal">customProperty</code><codeclass="literal">PropertySource</code> appears in any application that includes that jar on its classpath:</p><preclass="screen">org.springframework.cloud.bootstrap.BootstrapConfiguration=sample.custom.CustomPropertySourceLocator</pre></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="_environment_changes"href="#_environment_changes"></a>1.7 Environment Changes</h2></div></div></div><p>The application listens for an <codeclass="literal">EnvironmentChangeEvent</code> and reacts to the change in a couple of standard ways (additional <codeclass="literal">ApplicationListeners</code> can be added as <codeclass="literal">@Beans</code> by the user in the normal way).
When an <codeclass="literal">EnvironmentChangeEvent</code> is observed, it has a list of key values that have changed, and the application uses those to:</p><divclass="itemizedlist"><ulclass="itemizedlist"style="list-style-type: disc; "><liclass="listitem">Re-bind any <codeclass="literal">@ConfigurationProperties</code> beans in the context</li><liclass="listitem">Set the logger levels for any properties in <codeclass="literal">logging.level.*</code></li></ul></div><p>Note that the Config Client does not, by default, poll for changes in the <codeclass="literal">Environment</code>.
Generally, we would not recommend that approach for detecting changes (although you could set it up with a
If you have a scaled-out client application, it is better to broadcast the <codeclass="literal">EnvironmentChangeEvent</code> to all the instances instead of having them polling for changes (for example, by using the <aclass="link"href="https://github.com/spring-cloud/spring-cloud-bus"target="_top">Spring Cloud Bus</a>).</p><p>The <codeclass="literal">EnvironmentChangeEvent</code> covers a large class of refresh use cases, as long as you can actually make a change to the <codeclass="literal">Environment</code> and publish the event.
Note that those APIs are public and part of core Spring).
You can verify that the changes are bound to <codeclass="literal">@ConfigurationProperties</code> beans by visiting the <codeclass="literal">/configprops</code> endpoint (a normal Spring Boot Actuator feature).
For instance, a <codeclass="literal">DataSource</code> can have its <codeclass="literal">maxPoolSize</code> changed at runtime (the default <codeclass="literal">DataSource</code> created by Spring Boot is an <codeclass="literal">@ConfigurationProperties</code> bean) and grow capacity dynamically.
Re-binding <codeclass="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 <codeclass="literal">ApplicationContext</code>.
To address those concerns, we have <codeclass="literal">@RefreshScope</code>.</p></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="_refresh_scope"href="#_refresh_scope"></a>1.8 Refresh Scope</h2></div></div></div><p>When there is a configuration change, a Spring <codeclass="literal">@Bean</code> that is marked as <codeclass="literal">@RefreshScope</code> gets special treatment.
This feature addresses the problem of stateful beans that only get their configuration injected when they are initialized.
For instance, if a <codeclass="literal">DataSource</code> has open connections when the database URL is changed via the <codeclass="literal">Environment</code>, you probably want the holders of those connections to be able to complete what they are doing.
Then, the next time something borrows a connection from the pool, it gets one with the new URL.</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.
To force a bean to re-initialize on the next method call, you must invalidate its cache entry.</p><p>The <codeclass="literal">RefreshScope</code> is a bean in the context and has a public <codeclass="literal">refreshAll()</code> method to refresh all beans in the scope by clearing the target cache.
The <codeclass="literal">/refresh</code> endpoint exposes this functionality (over HTTP or JMX).
To refresh an individual bean by name, there is also a <codeclass="literal">refresh(String)</code> method.</p><p>To expose the <codeclass="literal">/refresh</code> endpoint, you need to add following configuration to your application:</p><preclass="programlisting"><spanxmlns:d="http://docbook.org/ns/docbook"class="hl-attribute">management</span>:
<spanxmlns:d="http://docbook.org/ns/docbook"class="hl-attribute"> include</span>: refresh</pre><divclass="note"style="margin-left: 0.5in; margin-right: 0.5in;"><tableborder="0"summary="Note"><tr><tdrowspan="2"align="center"valign="top"width="25"><imgalt="[Note]"src="images/note.png"></td><thalign="left">Note</th></tr><tr><tdalign="left"valign="top"><p><codeclass="literal">@RefreshScope</code> works (technically) on an <codeclass="literal">@Configuration</code> class, but it might lead to surprising behavior.
For example, it does not mean that all the <codeclass="literal">@Beans</code> defined in that class are themselves in <codeclass="literal">@RefreshScope</code>.
Specifically, anything that depends on those beans cannot rely on them being updated when a refresh is initiated, unless it is itself in <codeclass="literal">@RefreshScope</code>.
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 <codeclass="literal">@Configuration</code>).</p></td></tr></table></div></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="_encryption_and_decryption"href="#_encryption_and_decryption"></a>1.9 Encryption and Decryption</h2></div></div></div><p>Spring Cloud has an <codeclass="literal">Environment</code> pre-processor for decrypting property values locally.
It follows the same rules as the Config Server and has the same external configuration through <codeclass="literal">encrypt.*</code>.
Thus, you can use encrypted values in the form of <codeclass="literal">{cipher}*</code> and, as long as there is a valid key, they are decrypted before the main application context gets the <codeclass="literal">Environment</code> settings.
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.
See the following links for more information:</p><divclass="itemizedlist"><ulclass="itemizedlist"style="list-style-type: disc; "><liclass="listitem"><aclass="link"href="http://www.oracle.com/technetwork/java/javase/downloads/jce-6-download-429243.html"target="_top">Java 6 JCE</a></li><liclass="listitem"><aclass="link"href="http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html"target="_top">Java 7 JCE</a></li><liclass="listitem"><aclass="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><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="_endpoints"href="#_endpoints"></a>1.10 Endpoints</h2></div></div></div><p>For a Spring Boot Actuator application, some additional management endpoints are available. You can use:</p><divclass="itemizedlist"><ulclass="itemizedlist"style="list-style-type: disc; "><liclass="listitem"><codeclass="literal">POST</code> to <codeclass="literal">/actuator/env</code> to update the <codeclass="literal">Environment</code> and rebind <codeclass="literal">@ConfigurationProperties</code> and log levels.</li><liclass="listitem"><codeclass="literal">/actuator/refresh</code> to re-load the boot strap context and refresh the <codeclass="literal">@RefreshScope</code> beans.</li><liclass="listitem"><codeclass="literal">/actuator/restart</code> to close the <codeclass="literal">ApplicationContext</code> and restart it (disabled by default).</li><liclass="listitem"><codeclass="literal">/actuator/pause</code> and <codeclass="literal">/actuator/resume</code> for calling the <codeclass="literal">Lifecycle</code> methods (<codeclass="literal">stop()</code> and <codeclass="literal">start()</code> on the <codeclass="literal">ApplicationContext</code>).</li></ul></div></div></div><divclass="chapter"><divclass="titlepage"><div><div><h1class="title"><aname="_spring_cloud_commons_common_abstractions"href="#_spring_cloud_commons_common_abstractions"></a>2. Spring Cloud Commons: Common Abstractions</h1></div></div></div><p>Patterns such as service discovery, load balancing, and circuit breakers lend themselves to a common abstraction layer that can be consumed by all Spring Cloud clients, independent of the implementation (for example, discovery with Eureka or Consul).</p><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="__enablediscoveryclient"href="#__enablediscoveryclient"></a>2.1 @EnableDiscoveryClient</h2></div></div></div><p>Spring Cloud Commons provides the <codeclass="literal">@EnableDiscoveryClient</code> annotation.
This looks for implementations of the <codeclass="literal">DiscoveryClient</code> interface with <codeclass="literal">META-INF/spring.factories</code>.
Implementations of the Discovery Client add a configuration class to <codeclass="literal">spring.factories</code> under the <codeclass="literal">org.springframework.cloud.client.discovery.EnableDiscoveryClient</code> key.
Examples of <codeclass="literal">DiscoveryClient</code> implementations include <aclass="link"href="http://cloud.spring.io/spring-cloud-netflix/"target="_top">Spring Cloud Netflix Eureka</a>, <aclass="link"href="http://cloud.spring.io/spring-cloud-consul/"target="_top">Spring Cloud Consul Discovery</a>, and <aclass="link"href="http://cloud.spring.io/spring-cloud-zookeeper/"target="_top">Spring Cloud Zookeeper Discovery</a>.</p><p>By default, implementations of <codeclass="literal">DiscoveryClient</code> auto-register the local Spring Boot server with the remote discovery server.
This behavior can be disabled by setting <codeclass="literal">autoRegister=false</code> in <codeclass="literal">@EnableDiscoveryClient</code>.</p><divclass="note"style="margin-left: 0.5in; margin-right: 0.5in;"><tableborder="0"summary="Note"><tr><tdrowspan="2"align="center"valign="top"width="25"><imgalt="[Note]"src="images/note.png"></td><thalign="left">Note</th></tr><tr><tdalign="left"valign="top"><p><codeclass="literal">@EnableDiscoveryClient</code> is no longer required.
You can put a <codeclass="literal">DiscoveryClient</code> implementation on the classpath to cause the Spring Boot application to register with the service discovery server.</p></td></tr></table></div><divclass="section"><divclass="titlepage"><div><div><h3class="title"><aname="_health_indicator"href="#_health_indicator"></a>2.1.1 Health Indicator</h3></div></div></div><p>Commons creates a Spring Boot <codeclass="literal">HealthIndicator</code> that <codeclass="literal">DiscoveryClient</code> implementations can participate in by implementing <codeclass="literal">DiscoveryHealthIndicator</code>.
To disable the composite <codeclass="literal">HealthIndicator</code>, set <codeclass="literal">spring.cloud.discovery.client.composite-indicator.enabled=false</code>.
A generic <codeclass="literal">HealthIndicator</code> based on <codeclass="literal">DiscoveryClient</code> is auto-configured (<codeclass="literal">DiscoveryClientHealthIndicator</code>).
To disable it, set <codeclass="literal">spring.cloud.discovery.client.health-indicator.enabled=false</code>.
To disable the description field of the <codeclass="literal">DiscoveryClientHealthIndicator</code>, set <codeclass="literal">spring.cloud.discovery.client.health-indicator.include-description=false</code>.
Otherwise, it can bubble up as the <codeclass="literal">description</code> of the rolled up <codeclass="literal">HealthIndicator</code>.</p></div></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="_serviceregistry"href="#_serviceregistry"></a>2.2 ServiceRegistry</h2></div></div></div><p>Commons now provides a <codeclass="literal">ServiceRegistry</code> interface that provides methods such as <codeclass="literal">register(Registration)</code> and <codeclass="literal">deregister(Registration)</code>, which let you provide custom registered services.
<codeclass="literal">Registration</code> is a marker interface.</p><p>The following example shows the <codeclass="literal">ServiceRegistry</code> in use:</p><preclass="programlisting"><em><spanclass="hl-annotation"style="color: gray">@Configuration</span></em>
<spanxmlns:d="http://docbook.org/ns/docbook"class="hl-comment">// called through some external process, such as an event or a custom actuator endpoint</span>
}</pre><p>Each <codeclass="literal">ServiceRegistry</code> implementation has its own <codeclass="literal">Registry</code> implementation.</p><divclass="itemizedlist"><ulclass="itemizedlist"style="list-style-type: disc; "><liclass="listitem"><codeclass="literal">ZookeeperRegistration</code> used with <codeclass="literal">ZookeeperServiceRegistry</code></li><liclass="listitem"><codeclass="literal">EurekaRegistration</code> used with <codeclass="literal">EurekaServiceRegistry</code></li><liclass="listitem"><codeclass="literal">ConsulRegistration</code> used with <codeclass="literal">ConsulServiceRegistry</code></li></ul></div><p>If you are using the <codeclass="literal">ServiceRegistry</code> interface, you are going to need to pass the
correct <codeclass="literal">Registry</code> implementation for the <codeclass="literal">ServiceRegistry</code> implementation you
are using.</p><divclass="section"><divclass="titlepage"><div><div><h3class="title"><aname="_serviceregistry_auto_registration"href="#_serviceregistry_auto_registration"></a>2.2.1 ServiceRegistry Auto-Registration</h3></div></div></div><p>By default, the <codeclass="literal">ServiceRegistry</code> implementation auto-registers the running service.
* <codeclass="literal">@EnableDiscoveryClient(autoRegister=false)</code> to permanently disable auto-registration.
* <codeclass="literal">spring.cloud.service-registry.auto-registration.enabled=false</code> to disable the behavior through configuration.</p></div><divclass="section"><divclass="titlepage"><div><div><h3class="title"><aname="_service_registry_actuator_endpoint"href="#_service_registry_actuator_endpoint"></a>2.2.2 Service Registry Actuator Endpoint</h3></div></div></div><p>Spring Cloud Commons provides a <codeclass="literal">/service-registry</code> actuator endpoint.
This endpoint relies on a <codeclass="literal">Registration</code> bean in the Spring Application Context.
Calling <codeclass="literal">/service-registry</code> with GET returns the status of the <codeclass="literal">Registration</code>.
Using POST to the same endpoint with a JSON body changes the status of the current <codeclass="literal">Registration</code> to the new value.
The JSON body has to include the <codeclass="literal">status</code> field with the preferred value.
Please see the documentation of the <codeclass="literal">ServiceRegistry</code> implementation you use for the allowed values when updating the status and the values returned for the status.
For instance, Eureka’s supported statuses are <codeclass="literal">UP</code>, <codeclass="literal">DOWN</code>, <codeclass="literal">OUT_OF_SERVICE</code>, and <codeclass="literal">UNKNOWN</code>.</p></div></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="_spring_resttemplate_as_a_load_balancer_client"href="#_spring_resttemplate_as_a_load_balancer_client"></a>2.3 Spring RestTemplate as a Load Balancer Client</h2></div></div></div><p><codeclass="literal">RestTemplate</code> can be automatically configured to use ribbon.
To create a load-balanced <codeclass="literal">RestTemplate</code>, create a <codeclass="literal">RestTemplate</code><codeclass="literal">@Bean</code> and use the <codeclass="literal">@LoadBalanced</code> qualifier, as shown in the following example:</p><preclass="programlisting"><em><spanclass="hl-annotation"style="color: gray">@Configuration</span></em>
}</pre><divclass="caution"style="margin-left: 0.5in; margin-right: 0.5in;"><tableborder="0"summary="Caution"><tr><tdrowspan="2"align="center"valign="top"width="25"><imgalt="[Caution]"src="images/caution.png"></td><thalign="left">Caution</th></tr><tr><tdalign="left"valign="top"><p>A <codeclass="literal">RestTemplate</code> bean is no longer created through auto-configuration.
Individual applications must create it.</p></td></tr></table></div><p>The URI needs to use a virtual host name (that is, a service name, not a host name).
The Ribbon client is used to create a full physical address.
See <aclass="link"href="https://github.com/spring-cloud/spring-cloud-netflix/blob/master/spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/ribbon/RibbonAutoConfiguration.java"target="_top">RibbonAutoConfiguration</a> for details of how the <codeclass="literal">RestTemplate</code> is set up.</p></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="_spring_webclient_as_a_load_balancer_client"href="#_spring_webclient_as_a_load_balancer_client"></a>2.4 Spring WebClient as a Load Balancer Client</h2></div></div></div><p><codeclass="literal">WebClient</code> can be automatically configured to use the <codeclass="literal">LoadBalancerClient</code>.
To create a load-balanced <codeclass="literal">WebClient</code>, create a <codeclass="literal">WebClient.Builder</code><codeclass="literal">@Bean</code> and use the <codeclass="literal">@LoadBalanced</code> qualifier, as shown in the following example:</p><preclass="programlisting"><em><spanclass="hl-annotation"style="color: gray">@Configuration</span></em>
}</pre><p>The URI needs to use a virtual host name (that is, a service name, not a host name).
The Ribbon client is used to create a full physical address.</p><divclass="section"><divclass="titlepage"><div><div><h3class="title"><aname="_retrying_failed_requests"href="#_retrying_failed_requests"></a>2.4.1 Retrying Failed Requests</h3></div></div></div><p>A load-balanced <codeclass="literal">RestTemplate</code> can be configured to retry failed requests.
By default, this logic is disabled.
You can enable it by adding <aclass="link"href="https://github.com/spring-projects/spring-retry"target="_top">Spring Retry</a> to your application’s classpath.
The load-balanced <codeclass="literal">RestTemplate</code> honors some of the Ribbon configuration values related to retrying failed requests.
You can use <codeclass="literal">client.ribbon.MaxAutoRetries</code>, <codeclass="literal">client.ribbon.MaxAutoRetriesNextServer</code>, and <codeclass="literal">client.ribbon.OkToRetryOnAllOperations</code> properties.
If you would like to disable the retry logic with Spring Retry on the classpath, you can set <codeclass="literal">spring.cloud.loadbalancer.retry.enabled=false</code>.
See the <aclass="link"href="https://github.com/Netflix/ribbon/wiki/Getting-Started#the-properties-file-sample-clientproperties"target="_top">Ribbon documentation</a> for a description of what these properties do.</p><p>If you would like to implement a <codeclass="literal">BackOffPolicy</code> in your retries, you need to create a bean of type <codeclass="literal">LoadBalancedBackOffPolicyFactory</code> and return the <codeclass="literal">BackOffPolicy</code> you would like to use for a given service, as shown in the following example:</p><preclass="programlisting"><em><spanclass="hl-annotation"style="color: gray">@Configuration</span></em>
}</pre><divclass="note"style="margin-left: 0.5in; margin-right: 0.5in;"><tableborder="0"summary="Note"><tr><tdrowspan="2"align="center"valign="top"width="25"><imgalt="[Note]"src="images/note.png"></td><thalign="left">Note</th></tr><tr><tdalign="left"valign="top"><p><codeclass="literal">client</code> in the preceding examples should be replaced with your Ribbon client’s name.</p></td></tr></table></div><p>If you want to add one or more <codeclass="literal">RetryListener</code> implementations to your retry functionality, you need to
you would like to use for a given service, as shown in the following example:</p><preclass="programlisting"><em><spanclass="hl-annotation"style="color: gray">@Configuration</span></em>
}</pre></div></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="_multiple_resttemplate_objects"href="#_multiple_resttemplate_objects"></a>2.5 Multiple RestTemplate objects</h2></div></div></div><p>If you want a <codeclass="literal">RestTemplate</code> that is not load-balanced, create a <codeclass="literal">RestTemplate</code> bean and inject it.
To access the load-balanced <codeclass="literal">RestTemplate</code>, use the <codeclass="literal">@LoadBalanced</code> qualifier when you create your <codeclass="literal">@Bean</code>, as shown in the following example:\</p><preclass="programlisting"><em><spanclass="hl-annotation"style="color: gray">@Configuration</span></em>
}</pre><divclass="important"style="margin-left: 0.5in; margin-right: 0.5in;"><tableborder="0"summary="Important"><tr><tdrowspan="2"align="center"valign="top"width="25"><imgalt="[Important]"src="images/important.png"></td><thalign="left">Important</th></tr><tr><tdalign="left"valign="top"><p>Notice the use of the <codeclass="literal">@Primary</code> annotation on the plain <codeclass="literal">RestTemplate</code> declaration in the preceding example to disambiguate the unqualified <codeclass="literal">@Autowired</code> injection.</p></td></tr></table></div><divclass="tip"style="margin-left: 0.5in; margin-right: 0.5in;"><tableborder="0"summary="Tip"><tr><tdrowspan="2"align="center"valign="top"width="25"><imgalt="[Tip]"src="images/tip.png"></td><thalign="left">Tip</th></tr><tr><tdalign="left"valign="top"><p>If you see errors such as <codeclass="literal">java.lang.IllegalArgumentException: Can not set org.springframework.web.client.RestTemplate field com.my.app.Foo.restTemplate to com.sun.proxy.$Proxy89</code>, try injecting <codeclass="literal">RestOperations</code> or setting <codeclass="literal">spring.aop.proxyTargetClass=true</code>.</p></td></tr></table></div></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="loadbalanced-webclient"href="#loadbalanced-webclient"></a>2.6 Spring WebFlux WebClient as a Load Balancer Client</h2></div></div></div><p><codeclass="literal">WebClient</code> can be configured to use the <codeclass="literal">LoadBalancerClient</code>. <codeclass="literal">LoadBalancerExchangeFilterFunction</code> is auto-configured if <codeclass="literal">spring-webflux</code> is on the classpath. The following example shows how to configure a <codeclass="literal">WebClient</code> to use load balancer:</p><preclass="programlisting"><spanxmlns:d="http://docbook.org/ns/docbook"class="hl-keyword">public</span><spanxmlns:d="http://docbook.org/ns/docbook"class="hl-keyword">class</span> MyClass {
}</pre><p>The URI needs to use a virtual host name (that is, a service name, not a host name).
The <codeclass="literal">LoadBalancerClient</code> is used to create a full physical address.</p></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="ignore-network-interfaces"href="#ignore-network-interfaces"></a>2.7 Ignore Network Interfaces</h2></div></div></div><p>Sometimes, it is useful to ignore certain named network interfaces so that they can be excluded from Service Discovery registration (for example, when running in a Docker container).
A list of regular expressions can be set to cause the desired network interfaces to be ignored.
The following configuration ignores the <codeclass="literal">docker0</code> interface and all interfaces that start with <codeclass="literal">veth</code>:</p><p><b>application.yml. </b>
</p><p>You can also force the use of only specified network addresses by using a list of regular expressions, as shown in the following example:</p><p><b>bootstrap.yml. </b>
useOnlySiteLocalInterfaces: true</pre><p>See <aclass="link"href="https://docs.oracle.com/javase/8/docs/api/java/net/Inet4Address.html#isSiteLocalAddress--"target="_top">Inet4Address.html.isSiteLocalAddress()</a> for more details about what constitutes a site-local address.</p></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="http-clients"href="#http-clients"></a>2.8 HTTP Client Factories</h2></div></div></div><p>Spring Cloud Commons provides beans for creating both Apache HTTP clients (<codeclass="literal">ApacheHttpClientFactory</code>) and OK HTTP clients (<codeclass="literal">OkHttpClientFactory</code>).
The <codeclass="literal">OkHttpClientFactory</code> bean is created only if the OK HTTP jar is on the classpath.
In addition, Spring Cloud Commons provides beans for creating the connection managers used by both clients: <codeclass="literal">ApacheHttpClientConnectionManagerFactory</code> for the Apache HTTP client and <codeclass="literal">OkHttpClientConnectionPoolFactory</code> for the OK HTTP client.
If you would like to customize how the HTTP clients are created in downstream projects, you can provide your own implementation of these beans.
In addition, if you provide a bean of type <codeclass="literal">HttpClientBuilder</code> or <codeclass="literal">OkHttpClient.Builder</code>, the default factories use these builders as the basis for the builders returned to downstream projects.
You can also disable the creation of these beans by setting <codeclass="literal">spring.cloud.httpclientfactories.apache.enabled</code> or <codeclass="literal">spring.cloud.httpclientfactories.ok.enabled</code> to <codeclass="literal">false</code>.</p></div><divclass="section"><divclass="titlepage"><div><div><h2class="title"style="clear: both"><aname="enabled-features"href="#enabled-features"></a>2.9 Enabled Features</h2></div></div></div><p>Spring Cloud Commons provides a <codeclass="literal">/features</code> actuator endpoint.
This endpoint returns features available on the classpath and whether they are enabled.
The information returned includes the feature type, name, version, and vendor.</p><divclass="section"><divclass="titlepage"><div><div><h3class="title"><aname="_feature_types"href="#_feature_types"></a>2.9.1 Feature types</h3></div></div></div><p>There are two types of 'features': abstract and named.</p><p>Abstract features are features where an interface or abstract class is defined and that an implementation the creates, such as <codeclass="literal">DiscoveryClient</code>, <codeclass="literal">LoadBalancerClient</code>, or <codeclass="literal">LockService</code>.
The abstract class or interface is used to find a bean of that type in the context.
The version displayed is <codeclass="literal">bean.getClass().getPackage().getImplementationVersion()</code>.</p><p>Named features are features that do not have a particular class they implement, such as "Circuit Breaker", "API Gateway", "Spring Cloud Bus", and others. These features require a name and a bean type.</p></div><divclass="section"><divclass="titlepage"><div><div><h3class="title"><aname="_declaring_features"href="#_declaring_features"></a>2.9.2 Declaring features</h3></div></div></div><p>Any module can declare any number of <codeclass="literal">HasFeature</code> beans, as shown in the following examples:</p><preclass="programlisting"><em><spanclass="hl-annotation"style="color: gray">@Bean</span></em>
}</pre><p>Each of these beans should go in an appropriately guarded <codeclass="literal">@Configuration</code>.</p></div></div></div></div></body></html>
