Polish Liveness and Readiness support

This commit moves the core Liveness and Readiness support to its own
`availability` package. We've made this a core concept independent of
Kubernetes.

Spring Boot now produces `LivenessStateChanged` and
`ReadinessStateChanged` events as part of the typical application
lifecycle.

Liveness and Readiness Probes (`HealthIndicator` components and health
groups) are still configured only when deployed on Kubernetes.

This commit also improves the documentation around Probes best practices
and container lifecycle considerations.

See gh-19593

Author: bclozel

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/kubernetes/ProbesHealthContributorAutoConfiguration.java

@@ -17,16 +17,17 @@
 package org.springframework.boot.actuate.autoconfigure.kubernetes;
 
 import org.springframework.boot.actuate.autoconfigure.health.ConditionalOnEnabledHealthIndicator;
+import org.springframework.boot.actuate.availability.LivenessProbeHealthIndicator;
+import org.springframework.boot.actuate.availability.ReadinessProbeHealthIndicator;
 import org.springframework.boot.actuate.health.HealthEndpointGroupsRegistryCustomizer;
-import org.springframework.boot.actuate.kubernetes.LivenessProbeHealthIndicator;
 import org.springframework.boot.actuate.kubernetes.ProbesHealthEndpointGroupsRegistrar;
-import org.springframework.boot.actuate.kubernetes.ReadinessProbeHealthIndicator;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.autoconfigure.availability.ApplicationAvailabilityAutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnCloudPlatform;
-import org.springframework.boot.autoconfigure.kubernetes.ApplicationStateAutoConfiguration;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.availability.ApplicationAvailabilityProvider;
 import org.springframework.boot.cloud.CloudPlatform;
-import org.springframework.boot.kubernetes.ApplicationStateProvider;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
@@ -39,21 +40,23 @@
  */
 @Configuration(proxyBeanMethods = false)
 @ConditionalOnCloudPlatform(CloudPlatform.KUBERNETES)
-@AutoConfigureAfter(ApplicationStateAutoConfiguration.class)
+@AutoConfigureAfter(ApplicationAvailabilityAutoConfiguration.class)
 public class ProbesHealthContributorAutoConfiguration {
 
 	@Bean
 	@ConditionalOnEnabledHealthIndicator("livenessProbe")
+	@ConditionalOnMissingBean
 	public LivenessProbeHealthIndicator livenessProbeHealthIndicator(
-			ApplicationStateProvider applicationStateProvider) {
-		return new LivenessProbeHealthIndicator(applicationStateProvider);
+			ApplicationAvailabilityProvider applicationAvailabilityProvider) {
+		return new LivenessProbeHealthIndicator(applicationAvailabilityProvider);
 	}
 
 	@Bean
 	@ConditionalOnEnabledHealthIndicator("readinessProbe")
+	@ConditionalOnMissingBean
 	public ReadinessProbeHealthIndicator readinessProbeHealthIndicator(
-			ApplicationStateProvider applicationStateProvider) {
-		return new ReadinessProbeHealthIndicator(applicationStateProvider);
+			ApplicationAvailabilityProvider applicationAvailabilityProvider) {
+		return new ReadinessProbeHealthIndicator(applicationAvailabilityProvider);
 	}
 
 	@Bean

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/kubernetes/ProbesHealthContributorAutoConfigurationTests.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2012-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.autoconfigure.kubernetes;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.actuate.availability.LivenessProbeHealthIndicator;
+import org.springframework.boot.actuate.availability.ReadinessProbeHealthIndicator;
+import org.springframework.boot.actuate.health.HealthEndpointGroupsRegistryCustomizer;
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.autoconfigure.availability.ApplicationAvailabilityAutoConfiguration;
+import org.springframework.boot.availability.ApplicationAvailabilityProvider;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests fos {@link ProbesHealthContributorAutoConfiguration}.
+ *
+ * @author Brian Clozel
+ */
+class ProbesHealthContributorAutoConfigurationTests {
+
+	private ApplicationContextRunner contextRunner = new ApplicationContextRunner().withConfiguration(AutoConfigurations
+			.of(ApplicationAvailabilityAutoConfiguration.class, ProbesHealthContributorAutoConfiguration.class));
+
+	@Test
+	void probesNotConfiguredIfNotKubernetes() {
+		this.contextRunner.run((context) -> assertThat(context).hasSingleBean(ApplicationAvailabilityProvider.class)
+				.doesNotHaveBean(LivenessProbeHealthIndicator.class)
+				.doesNotHaveBean(ReadinessProbeHealthIndicator.class)
+				.doesNotHaveBean(HealthEndpointGroupsRegistryCustomizer.class));
+	}
+
+	@Test
+	void probesConfiguredIfKubernetes() {
+		this.contextRunner.withPropertyValues("spring.main.cloud-platform=kubernetes")
+				.run((context) -> assertThat(context).hasSingleBean(ApplicationAvailabilityProvider.class)
+						.hasSingleBean(LivenessProbeHealthIndicator.class)
+						.hasSingleBean(ReadinessProbeHealthIndicator.class)
+						.hasSingleBean(HealthEndpointGroupsRegistryCustomizer.class));
+	}
+
+}

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/kubernetes/LivenessProbeHealthIndicator.java renamed to spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/availability/LivenessProbeHealthIndicator.java

@@ -14,13 +14,13 @@
  * limitations under the License.
  */
 
-package org.springframework.boot.actuate.kubernetes;
+package org.springframework.boot.actuate.availability;
 
 import org.springframework.boot.actuate.health.AbstractHealthIndicator;
 import org.springframework.boot.actuate.health.Health;
 import org.springframework.boot.actuate.health.HealthIndicator;
-import org.springframework.boot.kubernetes.ApplicationStateProvider;
-import org.springframework.boot.kubernetes.LivenessState;
+import org.springframework.boot.availability.ApplicationAvailabilityProvider;
+import org.springframework.boot.availability.LivenessState;
 
 /**
  * A {@link HealthIndicator} that checks the {@link LivenessState} of the application.
@@ -30,15 +30,15 @@
  */
 public class LivenessProbeHealthIndicator extends AbstractHealthIndicator {
 
-	private final ApplicationStateProvider applicationStateProvider;
+	private final ApplicationAvailabilityProvider applicationAvailabilityProvider;
 
-	public LivenessProbeHealthIndicator(ApplicationStateProvider applicationStateProvider) {
-		this.applicationStateProvider = applicationStateProvider;
+	public LivenessProbeHealthIndicator(ApplicationAvailabilityProvider applicationAvailabilityProvider) {
+		this.applicationAvailabilityProvider = applicationAvailabilityProvider;
 	}
 
 	@Override
 	protected void doHealthCheck(Health.Builder builder) throws Exception {
-		if (LivenessState.live().equals(this.applicationStateProvider.getLivenessState())) {
+		if (LivenessState.live().equals(this.applicationAvailabilityProvider.getLivenessState())) {
 			builder.up();
 		}
 		else {

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/kubernetes/ReadinessProbeHealthIndicator.java renamed to spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/availability/ReadinessProbeHealthIndicator.java

@@ -14,13 +14,13 @@
  * limitations under the License.
  */
 
-package org.springframework.boot.actuate.kubernetes;
+package org.springframework.boot.actuate.availability;
 
 import org.springframework.boot.actuate.health.AbstractHealthIndicator;
 import org.springframework.boot.actuate.health.Health;
 import org.springframework.boot.actuate.health.HealthIndicator;
-import org.springframework.boot.kubernetes.ApplicationStateProvider;
-import org.springframework.boot.kubernetes.ReadinessState;
+import org.springframework.boot.availability.ApplicationAvailabilityProvider;
+import org.springframework.boot.availability.ReadinessState;
 
 /**
  * A {@link HealthIndicator} that checks the {@link ReadinessState} of the application.
@@ -30,15 +30,15 @@
  */
 public class ReadinessProbeHealthIndicator extends AbstractHealthIndicator {
 
-	private final ApplicationStateProvider applicationStateProvider;
+	private final ApplicationAvailabilityProvider applicationAvailabilityProvider;
 
-	public ReadinessProbeHealthIndicator(ApplicationStateProvider applicationStateProvider) {
-		this.applicationStateProvider = applicationStateProvider;
+	public ReadinessProbeHealthIndicator(ApplicationAvailabilityProvider applicationAvailabilityProvider) {
+		this.applicationAvailabilityProvider = applicationAvailabilityProvider;
 	}
 
 	@Override
 	protected void doHealthCheck(Health.Builder builder) throws Exception {
-		if (ReadinessState.ready().equals(this.applicationStateProvider.getReadinessState())) {
+		if (ReadinessState.ready().equals(this.applicationAvailabilityProvider.getReadinessState())) {
 			builder.up();
 		}
 		else {

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/availability/package-info.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Actuator support for application availability concerns.
+ */
+package org.springframework.boot.actuate.availability;

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/kubernetes/LivenessProbeHealthIndicatorTests.java renamed to spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/availability/LivenessProbeHealthIndicatorTests.java

@@ -14,14 +14,14 @@
  * limitations under the License.
  */
 
-package org.springframework.boot.actuate.kubernetes;
+package org.springframework.boot.actuate.availability;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.actuate.health.Status;
-import org.springframework.boot.kubernetes.ApplicationStateProvider;
-import org.springframework.boot.kubernetes.LivenessState;
+import org.springframework.boot.availability.ApplicationAvailabilityProvider;
+import org.springframework.boot.availability.LivenessState;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.BDDMockito.when;
@@ -34,13 +34,13 @@
  */
 class LivenessProbeHealthIndicatorTests {
 
-	private ApplicationStateProvider stateProvider;
+	private ApplicationAvailabilityProvider stateProvider;
 
 	private LivenessProbeHealthIndicator healthIndicator;
 
 	@BeforeEach
 	void setUp() {
-		this.stateProvider = mock(ApplicationStateProvider.class);
+		this.stateProvider = mock(ApplicationAvailabilityProvider.class);
 		this.healthIndicator = new LivenessProbeHealthIndicator(this.stateProvider);
 	}
 

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/kubernetes/ReadinessProbeHealthIndicatorTests.java renamed to spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/availability/ReadinessProbeHealthIndicatorTests.java

@@ -14,14 +14,14 @@
  * limitations under the License.
  */
 
-package org.springframework.boot.actuate.kubernetes;
+package org.springframework.boot.actuate.availability;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.actuate.health.Status;
-import org.springframework.boot.kubernetes.ApplicationStateProvider;
-import org.springframework.boot.kubernetes.ReadinessState;
+import org.springframework.boot.availability.ApplicationAvailabilityProvider;
+import org.springframework.boot.availability.ReadinessState;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.BDDMockito.when;
@@ -34,13 +34,13 @@
  */
 class ReadinessProbeHealthIndicatorTests {
 
-	private ApplicationStateProvider stateProvider;
+	private ApplicationAvailabilityProvider stateProvider;
 
 	private ReadinessProbeHealthIndicator healthIndicator;
 
 	@BeforeEach
 	void setUp() {
-		this.stateProvider = mock(ApplicationStateProvider.class);
+		this.stateProvider = mock(ApplicationAvailabilityProvider.class);
 		this.healthIndicator = new ReadinessProbeHealthIndicator(this.stateProvider);
 	}
 
@@ -51,8 +51,8 @@ void readinessIsReady() {
 	}
 
 	@Test
-	void readinessIsBusy() {
-		when(this.stateProvider.getReadinessState()).thenReturn(ReadinessState.busy());
+	void readinessIsUnready() {
+		when(this.stateProvider.getReadinessState()).thenReturn(ReadinessState.unready());
 		assertThat(this.healthIndicator.health().getStatus()).isEqualTo(Status.OUT_OF_SERVICE);
 	}
 

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/kubernetes/ApplicationStateAutoConfiguration.java renamed to spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/availability/ApplicationAvailabilityAutoConfiguration.java

@@ -14,34 +14,25 @@
  * limitations under the License.
  */
 
-package org.springframework.boot.autoconfigure.kubernetes;
+package org.springframework.boot.autoconfigure.availability;
 
-import org.springframework.boot.autoconfigure.condition.ConditionalOnCloudPlatform;
-import org.springframework.boot.cloud.CloudPlatform;
-import org.springframework.boot.kubernetes.ApplicationStateProvider;
-import org.springframework.boot.kubernetes.SpringApplicationEventListener;
+import org.springframework.boot.availability.ApplicationAvailabilityProvider;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
 /**
  * {@link org.springframework.boot.autoconfigure.EnableAutoConfiguration} for
- * {@link ApplicationStateProvider}.
+ * {@link ApplicationAvailabilityProvider}.
  *
  * @author Brian Clozel
  * @since 2.3.0
  */
 @Configuration(proxyBeanMethods = false)
-@ConditionalOnCloudPlatform(CloudPlatform.KUBERNETES)
-public class ApplicationStateAutoConfiguration {
+public class ApplicationAvailabilityAutoConfiguration {
 
 	@Bean
-	public ApplicationStateProvider applicationStateProvider() {
-		return new ApplicationStateProvider();
-	}
-
-	@Bean
-	public SpringApplicationEventListener springApplicationEventListener() {
-		return new SpringApplicationEventListener();
+	public ApplicationAvailabilityProvider applicationAvailabilityProvider() {
+		return new ApplicationAvailabilityProvider();
 	}
 
 }

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/kubernetes/package-info.java renamed to spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/availability/package-info.java

@@ -15,6 +15,6 @@
  */
 
 /**
- * Auto-configuration for Kubernetes application features.
+ * Auto-configuration for application availability features.
  */
-package org.springframework.boot.autoconfigure.kubernetes;
+package org.springframework.boot.autoconfigure.availability;

spring-boot-project/spring-boot-autoconfigure/src/main/resources/META-INF/spring.factories

@@ -89,7 +89,7 @@ org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
 org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
 org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
 org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
-org.springframework.boot.autoconfigure.kubernetes.ApplicationStateAutoConfiguration,\
+org.springframework.boot.autoconfigure.availability.ApplicationAvailabilityAutoConfiguration,\
 org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\
 org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\
 org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\