Introduce Sticky health indicator

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/health/HealthIndicatorAutoConfiguration.java

@@ -73,6 +73,12 @@ public HealthIndicatorRegistry healthIndicatorRegistry(
 		return HealthIndicatorRegistryBeans.get(applicationContext);
 	}
 
+	@Bean
+	public StickyHealthIndicatorDecoratorBeanPostProcessor stickyHealthIndicatorDecoratorBeanPostProcessor(
+		HealthIndicatorProperties properties) {
+		return new StickyHealthIndicatorDecoratorBeanPostProcessor(properties.getSticky());
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(Flux.class)
 	static class ReactiveHealthIndicatorConfiguration {

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/health/HealthIndicatorProperties.java

@@ -17,8 +17,10 @@
 package org.springframework.boot.actuate.autoconfigure.health;
 
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
 
@@ -42,6 +44,11 @@ public class HealthIndicatorProperties {
 	 */
 	private final Map<String, Integer> httpMapping = new HashMap<>();
 
+	/**
+	 * Health indicators that must always stay UP in case they were UP at least once.
+	 */
+	private Set<String> sticky = new HashSet<>();
+
 	public List<String> getOrder() {
 		return this.order;
 	}
@@ -56,4 +63,12 @@ public Map<String, Integer> getHttpMapping() {
 		return this.httpMapping;
 	}
 
+	public Set<String> getSticky() {
+		return sticky;
+	}
+
+	public void setSticky(Set<String> sticky) {
+		this.sticky = sticky;
+	}
+
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/health/StickyHealthIndicatorDecoratorBeanPostProcessor.java

@@ -0,0 +1,51 @@
+package org.springframework.boot.actuate.autoconfigure.health;
+
+import java.util.Collections;
+import java.util.Set;
+
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.config.BeanPostProcessor;
+import org.springframework.boot.actuate.health.HealthIndicator;
+import org.springframework.boot.actuate.health.HealthIndicatorNameFactory;
+import org.springframework.boot.actuate.health.StickyHealthIndicatorDecorator;
+
+/**
+ * Bean post processor that decorates Health Indicators with sticky UP status.
+ *
+ * @author Vladislav Fefelov
+ */
+public class StickyHealthIndicatorDecoratorBeanPostProcessor implements BeanPostProcessor {
+
+	private final HealthIndicatorNameFactory nameFactory;
+
+	private final Set<String> healthIndicatorNamesToDecorate;
+
+	public StickyHealthIndicatorDecoratorBeanPostProcessor(HealthIndicatorNameFactory nameFactory,
+														   Set<String> healthIndicatorNamesToDecorate) {
+		this.nameFactory = nameFactory;
+		this.healthIndicatorNamesToDecorate = healthIndicatorNamesToDecorate != null
+			? healthIndicatorNamesToDecorate : Collections.emptySet();
+	}
+
+	public StickyHealthIndicatorDecoratorBeanPostProcessor(Set<String> healthIndicatorNamesToDecorate) {
+		this(new HealthIndicatorNameFactory(), healthIndicatorNamesToDecorate);
+	}
+
+	@Override
+	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
+		if (!(bean instanceof HealthIndicator)) {
+			return bean;
+		}
+
+		final String healthIndicatorName = nameFactory.apply(beanName);
+
+		if (!healthIndicatorNamesToDecorate.contains(healthIndicatorName)) {
+			return bean;
+		}
+
+		final HealthIndicator healthIndicator = (HealthIndicator) bean;
+
+		return new StickyHealthIndicatorDecorator(healthIndicator);
+	}
+
+}

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

@@ -23,6 +23,7 @@ org.springframework.boot.actuate.autoconfigure.env.EnvironmentEndpointAutoConfig
 org.springframework.boot.actuate.autoconfigure.flyway.FlywayEndpointAutoConfiguration,\
 org.springframework.boot.actuate.autoconfigure.health.HealthEndpointAutoConfiguration,\
 org.springframework.boot.actuate.autoconfigure.health.HealthIndicatorAutoConfiguration,\
+org.springframework.boot.actuate.autoconfigure.health.StickyHealthIndicatorDecoratorAutoConfig,\
 org.springframework.boot.actuate.autoconfigure.influx.InfluxDbHealthIndicatorAutoConfiguration,\
 org.springframework.boot.actuate.autoconfigure.info.InfoContributorAutoConfiguration,\
 org.springframework.boot.actuate.autoconfigure.info.InfoEndpointAutoConfiguration,\

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/health/StickyHealthEndpointAutoConfigurationTests.java

@@ -0,0 +1,77 @@
+package org.springframework.boot.actuate.autoconfigure.health;
+
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.junit.Test;
+import org.springframework.boot.actuate.health.Health;
+import org.springframework.boot.actuate.health.HealthIndicator;
+import org.springframework.boot.actuate.health.Status;
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link StickyHealthIndicatorDecoratorBeanPostProcessor}.
+ *
+ * @author Vladislav Fefelov
+ * @since 20.03.2019
+ */
+public class StickyHealthEndpointAutoConfigurationTests {
+
+    private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
+        .withConfiguration(
+            AutoConfigurations.of(HealthIndicatorAutoConfiguration.class,
+                HealthEndpointAutoConfiguration.class));
+
+    @Test
+    public void healthEndpointMergeRegularAndReactive() {
+        this.contextRunner
+            .withPropertyValues("management.health.status.sticky[0]=simple")
+            .withUserConfiguration(HealthIndicatorConfiguration.class)
+            .run((context) -> {
+                AtomicReference<Health> indicatorState = context.getBean("simpleHealthIndicatorState",
+                    AtomicReference.class);
+                HealthIndicator indicator = context.getBean("simpleHealthIndicator",
+                    HealthIndicator.class);
+
+                Health initialDownState = Health.down().build();
+                indicatorState.set(initialDownState);
+
+                assertThat(indicator.health()).isSameAs(initialDownState);
+
+                Health upState = Health.up().build();
+                indicatorState.set(upState);
+
+                assertThat(indicator.health()).isSameAs(upState);
+
+                Health nextDownState = Health.down()
+                    .withDetail("custom", "detail")
+                    .build();
+                indicatorState.set(nextDownState);
+
+                assertThat(indicator.health().getStatus()).isEqualTo(Status.UP);
+                assertThat(indicator.health().getDetails().get("originalStatus")).isEqualTo(Status.DOWN);
+                assertThat(indicator.health().getDetails().get("originalDetails")).isEqualTo(nextDownState.getDetails());
+            });
+    }
+
+    @Configuration
+    static class HealthIndicatorConfiguration {
+
+        @Bean
+        public AtomicReference<Health> simpleHealthIndicatorState() {
+            return new AtomicReference<>(Health.up().build());
+        }
+
+        @Bean
+        public HealthIndicator simpleHealthIndicator() {
+            return simpleHealthIndicatorState()::get;
+        }
+
+    }
+
+
+}

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/StickyHealthIndicatorDecorator.java

@@ -0,0 +1,50 @@
+package org.springframework.boot.actuate.health;
+
+import org.springframework.util.Assert;
+
+/**
+ * Decorator for Health Indicator that suppresses any status except UP if
+ * actual status was UP at least once.
+ *
+ * @author Vladislav Fefelov
+ */
+public class StickyHealthIndicatorDecorator implements HealthIndicator {
+
+	private static final String ORIGINAL_STATUS_KEY = "originalStatus";
+
+	private static final String ORIGINAL_DETAILS_KEY = "originalDetails";
+
+	private final HealthIndicator delegate;
+
+	private volatile boolean wasUp = false;
+
+	public StickyHealthIndicatorDecorator(HealthIndicator healthIndicator) {
+		Assert.notNull(healthIndicator, "HealthIndicator cannot be null");
+		this.delegate = healthIndicator;
+	}
+
+	@Override
+	public Health health() {
+		final boolean previouslyWasUp = wasUp;
+
+		final Health actualHealth = delegate.health();
+
+		if (actualHealth.getStatus() == Status.UP) {
+			if (!previouslyWasUp) {
+				wasUp = true;
+			}
+
+			return actualHealth;
+		}
+
+		if (previouslyWasUp) {
+			return Health.up()
+				.withDetail(ORIGINAL_STATUS_KEY, actualHealth.getStatus())
+				.withDetail(ORIGINAL_DETAILS_KEY, actualHealth.getDetails())
+				.build();
+		}
+
+		return actualHealth;
+	}
+
+}