Merge branch '2.1.x' into 2.2.x

Closes gh-21091

spring-boot-project/spring-boot-docs/src/main/asciidoc/howto.adoc

@@ -2208,7 +2208,8 @@ See also the section on "`<<spring-boot-features.adoc#boot-features-error-handli
 
 
 [[howto-sanitize-sensible-values]]
-=== Sanitize sensible values
+[[howto-sanitize-sensitive-values]]
+=== Sanitize Sensitive Values
 Information returned by the `env` and `configprops` endpoints can be somewhat sensitive so keys matching a certain pattern are sanitized by default (i.e. their values are replaced by `+******+`).
 
 The patterns to use can be customized using the `management.endpoint.env.keys-to-sanitize` and `management.endpoint.configprops.keys-to-sanitize` respectively.
@@ -2220,6 +2221,22 @@ If any of the keys to sanitize are URI format (i.e. `<scheme>://<username>:<pass
 
 
 
+[[howto-map-health-indicators-to-metrics]]
+=== Map Health Indicators to Micrometer Metrics
+Spring Boot health indicators return a `Status` type to indicate the overall system health.
+If you want to monitor or alert on levels of health for a particular application, you can export these statuses as metrics via Micrometer.
+By default, the status codes "`up`", "`down`", "`out of service`" and "`unknown`" are used by Spring Boot.
+To export these, you'll need to convert these states to some set of numbers so that they can be used with a Micrometer `Gauge`.
+
+The follow example shows one way to write such an exporter:
+
+[source,java,indent=0,subs="verbatim,quotes,attributes"]
+----
+include::{code-examples}/actuate/metrics/MetricsHealthMicrometerExportExample.java[tag=configuration]
+----
+
+
+
 [[howto-security]]
 == Security
 This section addresses questions about security when working with Spring Boot, including questions that arise from using Spring Security with Spring Boot.

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/actuate/metrics/MetricsHealthMicrometerExportExample.java

@@ -0,0 +1,60 @@
+/*
+ * 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.docs.actuate.metrics;
+
+import io.micrometer.core.instrument.Gauge;
+import io.micrometer.core.instrument.MeterRegistry;
+
+import org.springframework.boot.actuate.health.HealthEndpoint;
+import org.springframework.boot.actuate.health.HealthIndicator;
+import org.springframework.boot.actuate.health.Status;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * Example to show how to export {@link HealthIndicator} beans to a {@link MeterRegistry}.
+ *
+ * @author Phillip Webb
+ */
+public class MetricsHealthMicrometerExportExample {
+
+	// tag::configuration[]
+	@Configuration
+	public class HealthMetricsConfiguration {
+
+		public HealthMetricsConfiguration(MeterRegistry registry, HealthEndpoint healthEndpoint) {
+			// This example presumes common tags (such as the app) are applied elsewhere
+			Gauge.builder("health", healthEndpoint, this::getStatusCode).strongReference(true).register(registry);
+		}
+
+		private int getStatusCode(HealthEndpoint health) {
+			Status status = health.health().getStatus();
+			if (Status.UP.equals(status)) {
+				return 3;
+			}
+			if (Status.OUT_OF_SERVICE.equals(status)) {
+				return 2;
+			}
+			if (Status.DOWN.equals(status)) {
+				return 1;
+			}
+			return 0;
+		}
+
+	}
+	// end::configuration[]
+
+}

spring-boot-project/spring-boot-docs/src/test/java/org/springframework/boot/docs/actuate/metrics/MetricsHealthMicrometerExportExampleTests.java

@@ -0,0 +1,78 @@
+/*
+ * 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.docs.actuate.metrics;
+
+import io.micrometer.core.instrument.Gauge;
+import io.micrometer.core.instrument.MeterRegistry;
+import io.micrometer.core.instrument.simple.SimpleMeterRegistry;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.actuate.autoconfigure.health.HealthContributorAutoConfiguration;
+import org.springframework.boot.actuate.autoconfigure.health.HealthEndpointAutoConfiguration;
+import org.springframework.boot.actuate.autoconfigure.metrics.MetricsAutoConfiguration;
+import org.springframework.boot.actuate.health.Health;
+import org.springframework.boot.actuate.health.HealthIndicator;
+import org.springframework.boot.autoconfigure.ImportAutoConfiguration;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Import;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link MetricsHealthMicrometerExportExample}.
+ *
+ * @author Phillip Webb
+ */
+@SpringBootTest
+public class MetricsHealthMicrometerExportExampleTests {
+
+	@Autowired
+	private MeterRegistry registry;
+
+	@Test
+	void registryExportsHealth() throws Exception {
+		Gauge gauge = this.registry.get("health").gauge();
+		assertThat(gauge.value()).isEqualTo(2);
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	@Import(MetricsHealthMicrometerExportExample.HealthMetricsConfiguration.class)
+	@ImportAutoConfiguration(classes = { HealthContributorAutoConfiguration.class, MetricsAutoConfiguration.class,
+			HealthEndpointAutoConfiguration.class })
+	static class Config {
+
+		@Bean
+		MetricsHealthMicrometerExportExample example() {
+			return new MetricsHealthMicrometerExportExample();
+		}
+
+		@Bean
+		SimpleMeterRegistry simpleMeterRegistry() {
+			return new SimpleMeterRegistry();
+		}
+
+		@Bean
+		HealthIndicator outOfService() {
+			return () -> new Health.Builder().outOfService().build();
+		}
+
+	}
+
+}