Spring boot | Actuator

1、简介

Spring Boot Actuator 是一个为生产环境准备（Production-ready Features）的功能，提供了对生产环境的管理和监控功能。使用只需要添加一个依赖就可以了。

<dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-actuator</artifactId>
    </dependency>

该功能由两子个项目组成，他的功能实现与配置都独立与spring-boot项目。

Actuator Boot.png

2、实现

它通过向web 容器注册自己的servlet 来实现，在actuator 项目中定义为Endpoint（servlet）, Endpoint实现类与请求的 URL向匹配。Operation与HTTP 方法对应，并且绑定Endpoint实现类的method。如何与SpringMVC DispatcherServlet 相兼容，见下文配置部分。

Operation vs HTTP-Method.png

1、注册servlet

org.springframework.boot.actuate.endpoint.web.ServletEndpointRegistrar

actuator 项目注册逻辑：

public class ServletEndpointRegistrar implements ServletContextInitializer {

public void onStartup(ServletContext servletContext) throws ServletException {
        this.servletEndpoints.forEach((servletEndpoint) -> register(servletContext, servletEndpoint));
    }

private void register(ServletContext servletContext, ExposableServletEndpoint endpoint) {
        String name = endpoint.getEndpointId().toLowerCaseString() + "-actuator-endpoint";
        String path = this.basePath + "/" + endpoint.getRootPath();
        String urlMapping = path.endsWith("/") ? path + "*" : path + "/*";
        EndpointServlet endpointServlet = endpoint.getEndpointServlet();
        Dynamic registration = servletContext.addServlet(name, endpointServlet.getServlet());
        registration.addMapping(urlMapping);
        registration.setInitParameters(endpointServlet.getInitParameters());
        registration.setLoadOnStartup(endpointServlet.getLoadOnStartup());
        logger.info("Registered '" + path + "' to " + name);
    }
}

actuator-autoconfigure
判断有没有DispatcherServlet，DispatcherServlet 会影响注册的servlet 匹配路径，实现了与DispatcherServlet 兼容配置。
ServletEndpointManagementContextConfiguration

    @Configuration(proxyBeanMethods = false)
    @ConditionalOnClass(DispatcherServlet.class)
    public static class WebMvcServletEndpointManagementContextConfiguration {

        @Bean
        public ServletEndpointRegistrar servletEndpointRegistrar(WebEndpointProperties properties,
                ServletEndpointsSupplier servletEndpointsSupplier, DispatcherServletPath dispatcherServletPath) {
            return new ServletEndpointRegistrar(dispatcherServletPath.getRelativePath(properties.getBasePath()),
                    servletEndpointsSupplier.getEndpoints());
        }

    }

    @Configuration(proxyBeanMethods = false)
    @ConditionalOnClass(ResourceConfig.class)
    @ConditionalOnMissingClass("org.springframework.web.servlet.DispatcherServlet")
    public static class JerseyServletEndpointManagementContextConfiguration {

        @Bean
        public ServletEndpointRegistrar servletEndpointRegistrar(WebEndpointProperties properties,
                ServletEndpointsSupplier servletEndpointsSupplier, JerseyApplicationPath jerseyApplicationPath) {
            return new ServletEndpointRegistrar(jerseyApplicationPath.getRelativePath(properties.getBasePath()),
                    servletEndpointsSupplier.getEndpoints());
        }

    }

实例化ServletEndpointRegistrar 依赖的ServletEndpointsSupplier。

@Configuration(proxyBeanMethods = false)
    @ConditionalOnWebApplication(type = Type.SERVLET)
    static class WebEndpointServletConfiguration {

        @Bean
        @ConditionalOnMissingBean(ServletEndpointsSupplier.class)
        ServletEndpointDiscoverer servletEndpointDiscoverer(ApplicationContext applicationContext,
                ObjectProvider<PathMapper> endpointPathMappers,
                ObjectProvider<EndpointFilter<ExposableServletEndpoint>> filters) {
            return new ServletEndpointDiscoverer(applicationContext,
                    endpointPathMappers.orderedStream().collect(Collectors.toList()),
                    filters.orderedStream().collect(Collectors.toList()));
        }

    }

ServletEndpointDiscoverer 会扫描SpringContext 里面被@Endpoint 注解的bean 定义。

    private Collection<EndpointBean> createEndpointBeans() {
.....
        String[] beanNames = BeanFactoryUtils.beanNamesForAnnotationIncludingAncestors(this.applicationContext,
                Endpoint.class);
.....   
        return byId.values();
    }

将EndpointBean 转换为ExposableEndpoint 然后在获取 EndpointServlet，这样就能注册到容器的中去。简言之，一个被@Endpoint注解的类，会被当成一个Servlet 注册到容器中。url 路径有默认值。

2、方法调用

通过http 请求的url 匹配（请求路径+请求方法）到对应的servlet ，由servlet 实现类调用到类里面具体的某一个方法。中间还有参数匹配与参数转换等等。。

3、HealthEndpoint

HealthEndpoint 是一个特殊的Endpoint，他对所有实现了HealthContributor 接口的bean 的聚合功能。

3.1 HealthEndpoint 类

请求health 接口时候会从 HealthContributorRegistry 注册中心返回匹配的HealthContributor ，然后调用getHealth方法。如果匹配到多个HealthContributor，将会聚合结果返回。

@Endpoint(id = "health")
public class HealthEndpoint extends HealthEndpointSupport<HealthContributor, HealthComponent>{

public HealthEndpoint(HealthContributorRegistry registry, HealthEndpointGroups groups) {
        super(registry, groups);
    }

@ReadOperation
    public HealthComponent health() {
        HealthComponent health = health(ApiVersion.V3, EMPTY_PATH);
        return (health != null) ? health : DEFAULT_HEALTH;
    }
」

3.2 自动配置部分
1、实例化HealthEndpoint
2、将所有实现了HealthContributor 接口部分的类注册到HealthContributorRegistry中。

@Configuration(proxyBeanMethods = false)
class HealthEndpointConfiguration {
    @Bean
    @ConditionalOnMissingBean
    HealthContributorRegistry healthContributorRegistry(ApplicationContext applicationContext,
            HealthEndpointGroups groups) {
        Map<String, HealthContributor> healthContributors = new LinkedHashMap<>(
                applicationContext.getBeansOfType(HealthContributor.class));
        if (ClassUtils.isPresent("reactor.core.publisher.Flux", applicationContext.getClassLoader())) {
            healthContributors.putAll(new AdaptedReactiveHealthContributors(applicationContext).get());
        }
        return new AutoConfiguredHealthContributorRegistry(healthContributors, groups.getNames());
    }

      @Bean
    @ConditionalOnMissingBean
    HealthEndpoint healthEndpoint(HealthContributorRegistry registry, HealthEndpointGroups groups) {
        return new HealthEndpoint(registry, groups);
    }


}

3.3 自定义 HealthContributor 举例

NacosConfigHealthIndicator 继承AbstractHealthIndicator

public class NacosConfigHealthIndicator extends AbstractHealthIndicator {

    private final ConfigService configService;

    public NacosConfigHealthIndicator(ConfigService configService) {
        this.configService = configService;
    }

    @Override
    protected void doHealthCheck(Health.Builder builder) throws Exception {
        // Just return "UP" or "DOWN"
        String status = configService.getServerStatus();
        // Set the status to Builder
        builder.status(status);
        switch (status) {
        case "UP":
            builder.up();
            break;
        case "DOWN":
            builder.down();
            break;
        default:
            builder.unknown();
            break;
        }
    }

}

添加bean 定义

    @Bean
    @ConditionalOnMissingBean
    @ConditionalOnEnabledHealthIndicator("nacos-config")
    public NacosConfigHealthIndicator nacosConfigHealthIndicator() {
        return new NacosConfigHealthIndicator(nacosConfigManager.getConfigService());
    }

访问health 接口将返回Nacos 配置状态。

小结：

对线上环境的监控非常重要，Spring Boot Actuator 为我们提供一些常用的监控和管理功能。我们在需要监控xx 的时候，可以先看下有没有现成的实现，它已经实现的大部分常用功能。我们在使用Spring Boot Actuator同时 ，还需要注意接口的安全性。避免非法调用，跨权限使用。

Spring-Boot-Actuator.png

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