聊聊Spring Cloud Config的ConfigClientWatch

序

Spring Cloud Config提供了一個ConfigClientWatch功能，能夠定時輪詢客戶端配置的狀態，若是狀態發生變化，則refresh。

配置文件

spring:
  cloud:
    config:
      uri: http://localhost:8888
      watch:
        enabled: true
        initialDelay: 5000 ##default 180000 ms
        delay: 10000 ##default 500 ms

配置類

spring-cloud-config-client-1.3.1.RELEASE-sources.jar!/org/springframework/cloud/config/client/ConfigClientAutoConfiguration.java

@Configuration
    @ConditionalOnClass(ContextRefresher.class)
    @ConditionalOnBean(ContextRefresher.class)
    @ConditionalOnProperty(value = "spring.cloud.config.watch.enabled")
    protected static class ConfigClientWatchConfiguration {

        @Bean
        public ConfigClientWatch configClientWatch(ContextRefresher contextRefresher) {
            return new ConfigClientWatch(contextRefresher);
        }
    }

ConfigClientWatch

public class ConfigClientWatch implements Closeable, EnvironmentAware {

    private static Log log = LogFactory
            .getLog(ConfigServicePropertySourceLocator.class);

    private final AtomicBoolean running = new AtomicBoolean(false);
    private final ContextRefresher refresher;
    private Environment environment;

    public ConfigClientWatch(ContextRefresher refresher) {
        this.refresher = refresher;
    }

    @Override
    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }

    @PostConstruct
    public void start() {
        this.running.compareAndSet(false, true);
    }

    @Scheduled(initialDelayString = "${spring.cloud.config.watch.initialDelay:180000}", fixedDelayString = "${spring.cloud.config.watch.delay:500}")
    public void watchConfigServer() {
        if (this.running.get()) {
            String newState = this.environment.getProperty("config.client.state");
            String oldState = ConfigClientStateHolder.getState();

            // only refresh if state has changed
            if (stateChanged(oldState, newState)) {
                ConfigClientStateHolder.setState(newState);
                this.refresher.refresh();
            }
        }
    }

    /* for testing */ boolean stateChanged(String oldState, String newState) {
        return (!hasText(oldState) && hasText(newState))
                || (hasText(oldState) && !oldState.equals(newState));
    }

    @Override
    public void close() {
        this.running.compareAndSet(true, false);
    }

}

依賴config.client.state的環境變量，來判斷client端配置文件的狀態
依賴ContextRefresher去刷新配置/實例

ContextRefresher

spring-cloud-context-1.2.2.RELEASE-sources.jar!/org/springframework/cloud/context/refresh/ContextRefresher.java

public synchronized Set<String> refresh() {
        Map<String, Object> before = extract(
                this.context.getEnvironment().getPropertySources());
        addConfigFilesToEnvironment();
        Set<String> keys = changes(before,
                extract(this.context.getEnvironment().getPropertySources())).keySet();
        this.context.publishEvent(new EnvironmentChangeEvent(keys));
        this.scope.refreshAll();
        return keys;
    }

這個refresh主要作兩件事情:

• 第一件是發佈EnvironmentChangeEvent事件

• 第二件是調用RefreshScope的refreshAll方法

EnvironmentChangeEvent的listener

spring-cloud-context-1.2.2.RELEASE-sources.jar!/org/springframework/cloud/context/properties/ConfigurationPropertiesRebinder.java

@Component
@ManagedResource
public class ConfigurationPropertiesRebinder
        implements ApplicationContextAware, ApplicationListener<EnvironmentChangeEvent> {

    private ConfigurationPropertiesBeans beans;

    private ConfigurationPropertiesBindingPostProcessor binder;

    private ApplicationContext applicationContext;

    private Map<String, Exception> errors = new ConcurrentHashMap<>();

    public ConfigurationPropertiesRebinder(
            ConfigurationPropertiesBindingPostProcessor binder,
            ConfigurationPropertiesBeans beans) {
        this.binder = binder;
        this.beans = beans;
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext)
            throws BeansException {
        this.applicationContext = applicationContext;
    }

    /**
     * A map of bean name to errors when instantiating the bean.
     *
     * @return the errors accumulated since the latest destroy
     */
    public Map<String, Exception> getErrors() {
        return this.errors;
    }

    @ManagedOperation
    public void rebind() {
        this.errors.clear();
        for (String name : this.beans.getBeanNames()) {
            rebind(name);
        }
    }

    @ManagedOperation
    public boolean rebind(String name) {
        if (!this.beans.getBeanNames().contains(name)) {
            return false;
        }
        if (this.applicationContext != null) {
            try {
                Object bean = this.applicationContext.getBean(name);
                if (AopUtils.isCglibProxy(bean)) {
                    bean = getTargetObject(bean);
                }
                this.binder.postProcessBeforeInitialization(bean, name);
                this.applicationContext.getAutowireCapableBeanFactory()
                        .initializeBean(bean, name);
                return true;
            }
            catch (RuntimeException e) {
                this.errors.put(name, e);
                throw e;
            }
        }
        return false;
    }

    @SuppressWarnings("unchecked")
    private static <T> T getTargetObject(Object candidate) {
        try {
            if (AopUtils.isAopProxy(candidate) && (candidate instanceof Advised)) {
                return (T) ((Advised) candidate).getTargetSource().getTarget();
            }
        }
        catch (Exception ex) {
            throw new IllegalStateException("Failed to unwrap proxied object", ex);
        }
        return (T) candidate;
    }

    @ManagedAttribute
    public Set<String> getBeanNames() {
        return new HashSet<String>(this.beans.getBeanNames());
    }

    @Override
    public void onApplicationEvent(EnvironmentChangeEvent event) {
        rebind();
    }

}

RefreshScope的refreshAll

spring-cloud-context-1.2.2.RELEASE-sources.jar!/org/springframework/cloud/context/scope/refresh/RefreshScope.java

@ManagedOperation(description = "Dispose of the current instance of all beans in this scope and force a refresh on next method execution.")
    public void refreshAll() {
        super.destroy();
        this.context.publishEvent(new RefreshScopeRefreshedEvent());
    }

發佈RefreshScopeRefreshedEvent事件

RefreshScopeRefreshedEvent事件listener

spring-cloud-netflix-eureka-client-1.3.1.RELEASE-sources.jar!/org/springframework/cloud/netflix/eureka/EurekaDiscoveryClientConfiguration.java

@Configuration
    @ConditionalOnClass(RefreshScopeRefreshedEvent.class)
    protected static class EurekaClientConfigurationRefresher {

        @Autowired(required = false)
        private EurekaClient eurekaClient;

        @Autowired(required = false)
        private EurekaAutoServiceRegistration autoRegistration;

        @EventListener(RefreshScopeRefreshedEvent.class)
        public void onApplicationEvent(RefreshScopeRefreshedEvent event) {
            //This will force the creation of the EurkaClient bean if not already created
            //to make sure the client will be reregistered after a refresh event
            if(eurekaClient != null) {
                eurekaClient.getApplications();
            }
            if (autoRegistration != null) {
                // register in case meta data changed
                this.autoRegistration.stop();
                this.autoRegistration.start();
            }
        }
    }

spring-cloud-netflix-core-1.2.6.RELEASE-sources.jar!/org/springframework/cloud/netflix/zuul/ZuulConfiguration.java

@Bean
    public ApplicationListener<ApplicationEvent> zuulRefreshRoutesListener() {
        return new ZuulRefreshListener();
    }
private static class ZuulRefreshListener
            implements ApplicationListener<ApplicationEvent> {

        @Autowired
        private ZuulHandlerMapping zuulHandlerMapping;

        private HeartbeatMonitor heartbeatMonitor = new HeartbeatMonitor();

        @Override
        public void onApplicationEvent(ApplicationEvent event) {
            if (event instanceof ContextRefreshedEvent
                    || event instanceof RefreshScopeRefreshedEvent
                    || event instanceof RoutesRefreshedEvent) {
                this.zuulHandlerMapping.setDirty(true);
            }
            else if (event instanceof HeartbeatEvent) {
                if (this.heartbeatMonitor.update(((HeartbeatEvent) event).getValue())) {
                    this.zuulHandlerMapping.setDirty(true);
                }
            }
        }

    }

小結

Spring Cloud Config的代碼是有提供ConfigClientWatch，可是實際單純使用git做爲config server的時候，拉取配置的時候獲得的state始終是null，所以客戶端輪詢是起不到刷新效果的。第二個就是這個refresh發佈的RefreshScopeRefreshedEvent，eureka會先去更新註冊信息爲DOWN，而後再UP起來，這個頻繁操做有點風險。