聊聊springboot的liveness及readiness

AvailabilityStateHealthIndicator继承了AbstractHealthIndicator，它定义了statusMappings，key为AvailabilityState，value为Status，其doHealthCheck就是获取state，然后从statusMappings取出对应的status

LivenessStateHealthIndicator

org/springframework/boot/actuate/availability/LivenessStateHealthIndicator.java

public class LivenessStateHealthIndicator extends AvailabilityStateHealthIndicator {

	public LivenessStateHealthIndicator(ApplicationAvailability availability) {
		super(availability, LivenessState.class, (statusMappings) -> {
			statusMappings.add(LivenessState.CORRECT, Status.UP);
			statusMappings.add(LivenessState.BROKEN, Status.DOWN);
		});
	}

	@Override
	protected AvailabilityState getState(ApplicationAvailability applicationAvailability) {
		return applicationAvailability.getLivenessState();
	}

}
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LivenessStateHealthIndicator继承了AvailabilityStateHealthIndicator，它建立了LivenessState.CORRECT到Status.UP，LivenessState.BROKEN到Status.DOWN的映射

ReadinessStateHealthIndicator

org/springframework/boot/actuate/availability/ReadinessStateHealthIndicator.java

public class ReadinessStateHealthIndicator extends AvailabilityStateHealthIndicator {

	public ReadinessStateHealthIndicator(ApplicationAvailability availability) {
		super(availability, ReadinessState.class, (statusMappings) -> {
			statusMappings.add(ReadinessState.ACCEPTING_TRAFFIC, Status.UP);
			statusMappings.add(ReadinessState.REFUSING_TRAFFIC, Status.OUT_OF_SERVICE);
		});
	}

	@Override
	protected AvailabilityState getState(ApplicationAvailability applicationAvailability) {
		return applicationAvailability.getReadinessState();
	}

}
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ReadinessStateHealthIndicator继承了AvailabilityStateHealthIndicator，它定义了ReadinessState.ACCEPTING_TRAFFIC到Status.UP，ReadinessState.REFUSING_TRAFFIC到Status.OUT_OF_SERVICE的映射

EventPublishingRunListener

org/springframework/boot/context/event/EventPublishingRunListener.java

public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {
	@Override
	public void started(ConfigurableApplicationContext context) {
		context.publishEvent(new ApplicationStartedEvent(this.application, this.args, context));
		AvailabilityChangeEvent.publish(context, LivenessState.CORRECT);
	}

	@Override
	public void running(ConfigurableApplicationContext context) {
		context.publishEvent(new ApplicationReadyEvent(this.application, this.args, context));
		AvailabilityChangeEvent.publish(context, ReadinessState.ACCEPTING_TRAFFIC);
	}
}
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EventPublishingRunListener的started方法会发布AvailabilityChangeEvent，其state为LivenessState.CORRECT；running方法会发布AvailabilityChangeEvent，其state为ReadinessState.ACCEPTING_TRAFFIC

SpringApplicationRunListeners

org/springframework/boot/SpringApplicationRunListeners.java

class SpringApplicationRunListeners {

	void started(ConfigurableApplicationContext context) {
		for (SpringApplicationRunListener listener : this.listeners) {
			listener.started(context);
		}
	}

	void running(ConfigurableApplicationContext context) {
		for (SpringApplicationRunListener listener : this.listeners) {
			listener.running(context);
		}
	}

	//......
}	
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SpringApplicationRunListeners的started会回调listener的started，running会回调listener的running方法

ServletWebServerApplicationContext

org/springframework/boot/web/servlet/context/ServletWebServerApplicationContext.java

public class ServletWebServerApplicationContext extends GenericWebApplicationContext
		implements ConfigurableWebServerApplicationContext {

	@Override
	protected void doClose() {
		if (isActive()) {
			AvailabilityChangeEvent.publish(this, ReadinessState.REFUSING_TRAFFIC);
		}
		super.doClose();
	}

	//......
}	
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ServletWebServerApplicationContext的doClose方法在active的时候会发布AvailabilityChangeEvent，state为ReadinessState.REFUSING_TRAFFIC

SpringApplication

org/springframework/boot/SpringApplication.java

public ConfigurableApplicationContext run(String... args) {
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		ConfigurableApplicationContext context = null;
		Collection exceptionReporters = new ArrayList<>();
		configureHeadlessProperty();
		SpringApplicationRunListeners listeners = getRunListeners(args);
		listeners.starting();
		try {
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
			ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
			configureIgnoreBeanInfo(environment);
			Banner printedBanner = printBanner(environment);
			context = createApplicationContext();
			exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
					new Class[] { ConfigurableApplicationContext.class }, context);
			prepareContext(context, environment, listeners, applicationArguments, printedBanner);
			refreshContext(context);
			afterRefresh(context, applicationArguments);
			stopWatch.stop();
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
			}
			listeners.started(context);
			callRunners(context, applicationArguments);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, listeners);
			throw new IllegalStateException(ex);
		}

		try {
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, null);
			throw new IllegalStateException(ex);
		}
		return context;
	}
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SpringApplication的run方法会先获取SpringApplicationRunListeners，然后执行listeners.starting()，接着prepareEnvironment、createApplicationContext、prepareContext、refreshContext、afterRefresh；之后执行listeners.started(context)；再执行listeners.running(context)

小结

AvailabilityHealthContributorAutoConfiguration定义了LivenessStateHealthIndicator、ReadinessStateHealthIndicator，它们依赖AvailabilityChangeEvent，SpringApplication的run方法会先后触发listeners.starting()、listeners.started(context)、listeners.running(context)；EventPublishingRunListener的started方法会发布AvailabilityChangeEvent，其state为LivenessState.CORRECT；running方法会发布AvailabilityChangeEvent，其state为ReadinessState.ACCEPTING_TRAFFIC。