Spring Cloud实战：构建云原生应用与配置服务

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本文档主要介绍了Spring Boot Cloud的案例分享，着重探讨了Spring Cloud框架的核心特性和功能模块。Spring Cloud是一个基于Spring Boot的云原生应用开发工具集，旨在简化微服务架构的应用部署、配置管理和通信。以下是文档中提到的一些关键知识点： 1. **云原生应用特性**： Spring Cloud支持构建云原生应用程序，它关注于将应用程序设计成可扩展、可靠且易于部署的服务。通过与Kubernetes、Docker等云基础设施集成，实现服务发现、负载均衡和自动配置。 2. **Spring Cloud Context：ApplicationContext Services** - **Bootstrap ApplicationContext**：这是启动时创建的第一个应用上下文，用于处理早期启动时的配置和服务注册。 - **Application Context Hierarchies**：Spring Cloud允许创建多级应用上下文，以便管理不同环境（如开发、测试、生产）的配置。 - **配置位置和远程属性**：可以通过修改Bootstrap Properties的位置或覆盖远程属性来定制应用的初始配置。 - **Bootstrap Configuration定制**：允许用户自定义启动时的配置行为。 - **Bootstrap Property Sources**：用户可以扩展或定制初始化的属性源列表。 - **环境变化管理**：Spring Cloud能够动态响应环境变量的变化，如从环境配置文件获取配置。 - **Refresh Scope**：通过Spring的`@RefreshScope`注解，允许在运行时刷新配置。 - **加密和解密**：Spring Cloud提供了安全的配置存储和传输，支持加密和解密功能。 - **Endpoins**：提供API来管理服务实例和健康检查。 3. **Spring Cloud Commons：通用抽象** - **`@EnableDiscoveryClient`**：这是一个注解，用于自动注册服务到服务注册中心，并提供健康检查功能。 - **Health Indicator**：帮助监控服务的健康状态，例如检查依赖项是否可用。 - **Service Registry**：服务注册与发现机制，包括自动注册和Actuator端点的管理。 - **Spring RestTemplate作为负载均衡客户端**：支持使用RestTemplate访问服务，可以处理重试请求。 - **Multiple RestTemplate objects**：允许创建多个RestTemplate实例，满足不同的需求。 - **忽略网络接口**：提供选项来排除特定的网络接口，适用于私有网络环境。 - **HTTP Client Factories**：定制HTTP客户端，支持自定义连接池和超时设置。 4. **Spring Cloud Config：快速入门与配置服务器** - **客户端使用**：Spring Cloud Config客户端负责从配置服务器获取应用的配置信息。 - **配置服务器**：配置服务器存储和分发应用程序的配置数据，支持多种环境仓库（如Git、GitHub、本地文件）。 - **Environment Repository**：环境存储库用于管理不同环境的配置数据，如开发、测试、生产。这些知识点展示了Spring Boot Cloud的强大功能，以及如何利用它构建和管理微服务架构中的各个组件。通过深入了解和实践，开发者可以更好地利用Spring Cloud提高开发效率和应用的可扩展性。

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A Spring Cloud application operates by creating a "bootstrap" context, which is a parent context for the main application. Out of the box it is

responsible for loading configuration properties from the external sources, and also decrypting properties in the local external configuration

files. The two contexts share an Environment which is the source of external properties for any Spring application. Bootstrap properties are

added with high precedence, so they cannot be overridden by local configuration, by default.

The bootstrap context uses a different convention for locating external configuration than the main application context, so instead of

application.yml (or .properties ) you use bootstrap.yml , keeping the external configuration for bootstrap and main context nicely

separate. Example:

bootstrap.yml.

spring:

application:

name: foo

cloud:

config:

uri: ${SPRING_CONFIG_URI:http://localhost:8888}

It is a good idea to set the spring.application.name (in bootstrap.yml or application.yml ) if your application needs any application-

specific configuration from the server.

You can disable the bootstrap process completely by setting spring.cloud.bootstrap.enabled=false (e.g. in System properties).

2.2 Application Context Hierarchies

If you build an application context from SpringApplication or SpringApplicationBuilder , 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 will contain additional property sources, compared to building the same context without Spring Cloud Config. The additional

property sources are:

"bootstrap": an optional CompositePropertySource appears with high priority if any PropertySourceLocators are found in the

Bootstrap context, and they have non-empty properties. An example would be properties from the Spring Cloud Config Server. See below

for instructions on how to customize the contents of this property source.

"applicationConfig: [classpath:bootstrap.yml]" (and friends if Spring profiles are active). If you have a bootstrap.yml (or properties) then

those properties are used to configure the Bootstrap context, and then they get added to the child context when its parent is set. They have

lower precedence than the application.yml (or properties) 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 below for instructions on how to customize the contents of these property

sources.

Because of the ordering rules of property sources the "bootstrap" entries take precedence, but note that these do not contain any data from

bootstrap.yml , which has very low precedence, but can be used to set defaults.

You can extend the context hierarchy by simply setting the parent context of any ApplicationContext you create, e.g. using its own

interface, or with the SpringApplicationBuilder convenience methods ( parent() , child() and sibling() ). The bootstrap context will

be the parent of the most senior ancestor that you create yourself. Every context in the hierarchy will have its own "bootstrap" property source

(possibly empty) to avoid promoting values inadvertently from parents down to their descendants. Every context in the hierarchy can also (in

principle) have a different spring.application.name and hence a different remote property source if there is a Config Server. Normal Spring

application context behaviour 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 one from the parent is not included in the

child).

Note that the SpringApplicationBuilder allows you to share an Environment 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 will share common things with

their parent.

2.3 Changing the Location of Bootstrap Properties

The bootstrap.yml (or .properties ) location can be specified using spring.cloud.bootstrap.name (default "bootstrap") or

spring.cloud.bootstrap.location (default empty), e.g. in System properties. Those properties behave like the spring.config.*

variants with the same name, in fact they are used to set up the bootstrap ApplicationContext by setting those properties in its

Environment . If there is an active profile (from spring.profiles.active or through the Environment API in the context you are building)

then properties in that profile will be loaded as well, just like in a regular Spring Boot app, e.g. from bootstrap-development.properties for

a "development" profile.

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2.4 Overriding the Values of Remote Properties

The property sources that are added to you application by the bootstrap context are often "remote" (e.g. from a Config Server), and by default

they cannot be overridden locally, except on the command line. If you want to allow your applications to override the remote properties with

their own System properties or config files, the remote property source has to grant it permission by setting

spring.cloud.config.allowOverride=true (it doesn’t work to set this locally). Once that flag is set there are some finer grained settings to

control the location of the remote properties in relation to System properties and the application’s local configuration:

spring.cloud.config.overrideNone=true to override with any local property source, and

spring.cloud.config.overrideSystemProperties=false if only System properties and env vars should override the remote settings, but

not the local config files.

2.5 Customizing the Bootstrap Configuration

The bootstrap context can be trained to do anything you like by adding entries to /META-INF/spring.factories under the key

org.springframework.cloud.bootstrap.BootstrapConfiguration . This is a comma-separated list of Spring @Configuration classes

which will be used to create the context. Any beans that you want to be available to the main application context for autowiring can be created

here, and also there is a special contract for @Beans of type ApplicationContextInitializer . Classes can be marked with an @Order if

you want to control the startup sequence (the default order is "last").

Be careful when adding custom BootstrapConfiguration that the classes you add are not @ComponentScanned by mistake

into your "main" application context, where they might not be needed. Use a separate package name for boot configuration

classes that is not already covered by your @ComponentScan or @SpringBootApplication annotated configuration classes.

The bootstrap process ends by injecting initializers into the main SpringApplication instance (i.e. the normal Spring Boot startup sequence,

whether it is running as a standalone app or deployed in an application server). First a bootstrap context is created from the classes found in

spring.factories and then all @Beans of type ApplicationContextInitializer are added to the main SpringApplication before it

is started.

2.6 Customizing the Bootstrap Property Sources

The default property source for external configuration added by the bootstrap process is the Config Server, but you can add additional sources

by adding beans of type PropertySourceLocator to the bootstrap context (via spring.factories ). You could use this to insert additional

properties from a different server, or from a database, for instance.

As an example, consider the following trivial custom locator:

@Configuration

public class CustomPropertySourceLocator implements PropertySourceLocator {

@Override

public PropertySource<?> locate(Environment environment) {

return new MapPropertySource("customProperty",

Collections.<String, Object>singletonMap("property.from.sample.custom.source", "worked as intended"));

}

The Environment that is passed in is the one for the ApplicationContext about to be created, i.e. the one that we are supplying additional

property sources for. It will already have its normal Spring Boot-provided property sources, so you can use those to locate a property source

specific to this Environment (e.g. by keying it on the spring.application.name , as is done in the default Config Server property source

locator).

If you create a jar with this class in it and then add a META-INF/spring.factories containing:

org.springframework.cloud.bootstrap.BootstrapConfiguration=sample.custom.CustomPropertySourceLocator

then the "customProperty" PropertySource will show up in any application that includes that jar on its classpath.

2.7 Environment Changes

The application will listen for an EnvironmentChangeEvent and react to the change in a couple of standard ways (additional

ApplicationListeners can be added as @Beans by the user in the normal way). When an EnvironmentChangeEvent is observed it will

have a list of key values that have changed, and the application will use those to:

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Re-bind any @ConfigurationProperties beans in the context

Set the logger levels for any properties in logging.level.*

Note that the Config Client does not by default poll for changes in the Environment , and generally we would not recommend that approach for

detecting changes (although you could set it up with a @Scheduled annotation). If you have a scaled-out client application then it is better to

broadcast the EnvironmentChangeEvent to all the instances instead of having them polling for changes (e.g. using the Spring Cloud Bus).

The EnvironmentChangeEvent covers a large class of refresh use cases, as long as you can actually make a change to the Environment

and publish the event (those APIs are public and part of core Spring). You can verify the changes are bound to @ConfigurationProperties

beans by visiting the /configprops endpoint (normal Spring Boot Actuator feature). For instance a DataSource can have its maxPoolSize

changed at runtime (the default DataSource created by Spring Boot is an @ConfigurationProperties bean) and grow capacity

dynamically. Re-binding @ConfigurationProperties 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 ApplicationContext . To address those concerns we have

@RefreshScope .

2.8 Refresh Scope

A Spring @Bean that is marked as @RefreshScope will get special treatment when there is a configuration change. This addresses the

problem of stateful beans that only get their configuration injected when they are initialized. For instance if a DataSource has open

connections when the database URL is changed via the Environment , we probably want the holders of those connections to be able to

complete what they are doing. Then the next time someone borrows a connection from the pool he gets one with the new URL.

Refresh scope beans are lazy proxies that initialize when they are used (i.e. 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 just need to invalidate its cache entry.

The RefreshScope is a bean in the context and it has a public method refreshAll() to refresh all beans in the scope by clearing the target

cache. There is also a refresh(String) method to refresh an individual bean by name. This functionality is exposed in the /refresh

endpoint (over HTTP or JMX).

@RefreshScope works (technically) on an @Configuration class, but it might lead to surprising behaviour: e.g. it does not

mean that all the @Beans defined in that class are themselves @RefreshScope . Specifically, anything that depends on those

beans cannot rely on them being updated when a refresh is initiated, unless it is itself in @RefreshScope (in which it will be

rebuilt on a refresh and its dependencies re-injected, at which point they will be re-initialized from the refreshed

@Configuration ).

2.9 Encryption and Decryption

Spring Cloud has an Environment pre-processor for decrypting property values locally. It follows the same rules as the Config Server, and

has the same external configuration via encrypt.* . Thus you can use encrypted values in the form {cipher}* and as long as there is a

valid key then they will be decrypted before the main application context gets the Environment . 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.

If you are getting an exception due to "Illegal key size" and you are using Sun’s JDK, you need to install the Java Cryptography Extension

(JCE) Unlimited Strength Jurisdiction Policy Files. See the following links for more information:

Java 6 JCE

Java 7 JCE

Java 8 JCE

Extract files into JDK/jre/lib/security folder (whichever version of JRE/JDK x64/x86 you are using).

2.10 Endpoints

For a Spring Boot Actuator application there are some additional management endpoints:

POST to /env to update the Environment and rebind @ConfigurationProperties and log levels

/refresh for re-loading the boot strap context and refreshing the @RefreshScope beans

/restart for closing the ApplicationContext and restarting it (disabled by default)

/pause and /resume for calling the Lifecycle methods ( stop() and start() on the ApplicationContext )

3. Spring Cloud Commons: Common Abstractions

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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 (e.g. discovery via Eureka or Consul).

3.1 @EnableDiscoveryClient

Commons provides the @EnableDiscoveryClient annotation. This looks for implementations of the DiscoveryClient interface via

META-INF/spring.factories . Implementations of Discovery Client will add a configuration class to spring.factories under the

org.springframework.cloud.client.discovery.EnableDiscoveryClient key. Examples of DiscoveryClient implementations: are

Spring Cloud Netflix Eureka, Spring Cloud Consul Discovery and Spring Cloud Zookeeper Discovery.

By default, implementations of DiscoveryClient will auto-register the local Spring Boot server with the remote discovery server. This can be

disabled by setting autoRegister=false in @EnableDiscoveryClient .

The use of @EnableDiscoveryClient is no longer required. It is enough to just have a DiscoveryClient implementation on

the classpath to cause the Spring Boot application to register with the service discovery server.

3.1.1 Health Indicator

Commons creates a Spring Boot HealthIndicator that DiscoveryClient implementations can participate in by implementing

DiscoveryHealthIndicator . To disable the composite HealthIndicator set

spring.cloud.discovery.client.composite-indicator.enabled=false . A generic HealthIndicator based on DiscoveryClient is

auto-configured

( DiscoveryClientHealthIndicator). To disable it, set `spring.cloud.discovery.client.health-indicator.enabled=false .

To disable the description field of the DiscoveryClientHealthIndicator set

spring.cloud.discovery.client.health-indicator.include-description=false , otherwise it can bubble up as the description of

the rolled up HealthIndicator .

3.2 ServiceRegistry

Commons now provides a ServiceRegistry interface which provides methods like register(Registration) and

deregister(Registration) which allow you to provide custom registered services. Registration is a marker interface.

@Configuration

@EnableDiscoveryClient(autoRegister=false)

public class MyConfiguration {

private ServiceRegistry registry;

public MyConfiguration(ServiceRegistry registry) {

this.registry = registry;

}

// called via some external process, such as an event or a custom actuator endpoint

public void register() {

Registration registration = constructRegistration();

this.registry.register(registration);

}

Each ServiceRegistry implementation has its own Registry implementation.

3.2.1 ServiceRegistry Auto-Registration

By default, the ServiceRegistry implementation will auto-register the running service. To disable that behavior, there are two methods. You

can set @EnableDiscoveryClient(autoRegister=false) to permanently disable auto-registration. You can also set

spring.cloud.service-registry.auto-registration.enabled=false to disable the behavior via configuration.

3.2.2 Service Registry Actuator Endpoint

A /service-registry actuator endpoint is provided by Commons. This endpoint relys on a Registration bean in the Spring Application

Context. Calling /service-registry/instance-status via a GET will return the status of the Registration . A POST to the same

endpoint with a String body will change the status of the current Registration to the new value. Please see the documentation of the

ServiceRegistry implementation you are using for the allowed values for updating the status and the values retured for the status.

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3.3 Spring RestTemplate as a Load Balancer Client

RestTemplate can be automatically configured to use ribbon. To create a load balanced RestTemplate create a RestTemplate @Bean

and use the @LoadBalanced qualifier.

A RestTemplate bean is no longer created via auto configuration. It must be created by individual applications.

@Configuration

public class MyConfiguration {

@LoadBalanced

@Bean

RestTemplate restTemplate() {

return new RestTemplate();

}

public class MyClass {

@Autowired

private RestTemplate restTemplate;

public String doOtherStuff() {

String results = restTemplate.getForObject("http://stores/stores", String.class);

return results;

}

The URI needs to use a virtual host name (ie. service name, not a host name). The Ribbon client is used to create a full physical address. See

RibbonAutoConfiguration for details of how the RestTemplate is set up.

3.3.1 Retrying Failed Requests

A load balanced RestTemplate can be configured to retry failed requests. By default this logic is disabled, you can enable it by adding Spring

Retry to your application’s classpath. The load balanced RestTemplate will honor some of the Ribbon configuration values related to retrying

failed requests. If you would like to disable the retry logic with Spring Retry on the classpath you can set

spring.cloud.loadbalancer.retry.enabled=false . The properties you can use are client.ribbon.MaxAutoRetries ,

client.ribbon.MaxAutoRetriesNextServer , and client.ribbon.OkToRetryOnAllOperations . See the Ribbon documentation for a

description of what there properties do.

If you would like to implement a BackOffPolicy in your retries you will need to create a bean of type

LoadBalancedBackOffPolicyFactory , and return the BackOffPolicy you would like to use for a given service.

@Configuration

public class MyConfiguration {

@Bean

LoadBalancedBackOffPolicyFactory backOffPolciyFactory() {

return new LoadBalancedBackOffPolicyFactory() {

@Override

public BackOffPolicy createBackOffPolicy(String service) {

return new ExponentialBackOffPolicy();

}

};

}

client in the above examples should be replaced with your Ribbon client’s name.

If you want to add one or more RetryListener to your retry you will need to create a bean of type LoadBalancedRetryListenerFactory

and return the RetryListener array you would like to use for a given service.

@Configuration

public class MyConfiguration {

@Bean

LoadBalancedRetryListenerFactory retryListenerFactory() {

return new LoadBalancedRetryListenerFactory() {

@Override

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