Collect metrics for application instances (#4270)

docs/modules/ROOT/pages/spring-cloud-netflix.adoc

@@ -604,6 +604,17 @@ when running a Eureka server you must include these dependencies in your POM or
 
 Spring Cloud Netflix Eureka Server does not support Spring AOT transformations or native images.
 
+=== Metrics
+
+`EurekaInstanceMonitor` listens to events related to Eureka instance registration and creates/updates `Gauge`s for Eureka instance information in Micrometer's `MeterRegistry`. By default, this behavior is disabled. If you want to enable it, you need to set `eureka.server.metrics.enabled` to `true`.
+
+By default, the `Gauge`s are named `eureka.server.instances` and have the following tags:
+
+- `application`: application name
+- `status`: instance status (`UP`, `DOWN`, `STARTING`, `OUT_OF_SERVICE`, `UNKNOWN`, see: `com.netflix.appinfo.InstanceInfo.InstanceStatus`)
+
+You can add additional tags by injecting your own implementation of `EurekaInstanceTagsProvider`.
+
 == Configuration properties
 
 To see the list of all Spring Cloud Netflix related configuration properties please check link:appendix.html[the Appendix page].

spring-cloud-netflix-eureka-server/src/main/java/org/springframework/cloud/netflix/eureka/server/metrics/DefaultEurekaInstanceTagsProvider.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2013-2024 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.cloud.netflix.eureka.server.metrics;
+
+import com.netflix.appinfo.InstanceInfo;
+import io.micrometer.core.instrument.Tag;
+import io.micrometer.core.instrument.Tags;
+
+/**
+ * Default implementation for {@link EurekaInstanceTagsProvider}.
+ *
+ * @author Wonchul Heo
+ * @since 4.1.2
+ */
+class DefaultEurekaInstanceTagsProvider implements EurekaInstanceTagsProvider {
+
+	@Override
+	public Tags eurekaInstanceTags(InstanceInfo instanceInfo) {
+		return Tags.of(Tag.of("application", instanceInfo.getAppName()),
+				Tag.of("status", instanceInfo.getStatus().name()));
+	}
+
+}

spring-cloud-netflix-eureka-server/src/main/java/org/springframework/cloud/netflix/eureka/server/metrics/EurekaInstanceMetricsAutoConfiguration.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2013-2024 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.cloud.netflix.eureka.server.metrics;
+
+import com.netflix.eureka.registry.PeerAwareInstanceRegistry;
+import io.micrometer.core.instrument.MeterRegistry;
+
+import org.springframework.boot.actuate.autoconfigure.metrics.CompositeMeterRegistryAutoConfiguration;
+import org.springframework.boot.actuate.autoconfigure.metrics.MetricsAutoConfiguration;
+import org.springframework.boot.autoconfigure.AutoConfigureAfter;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration;
+import org.springframework.context.annotation.Bean;
+
+/**
+ * Auto-configuration for Eureka Instance metrics.
+ *
+ * @author Wonchul Heo
+ * @since 4.1.2
+ */
+@ConditionalOnClass(MeterRegistry.class)
+@ConditionalOnBean(MeterRegistry.class)
+@AutoConfigureAfter({ MetricsAutoConfiguration.class, CompositeMeterRegistryAutoConfiguration.class,
+		EurekaServerAutoConfiguration.class })
+@ConditionalOnProperty(name = "eureka.server.metrics.enabled", havingValue = "true")
+class EurekaInstanceMetricsAutoConfiguration {
+
+	@ConditionalOnMissingBean
+	@Bean
+	public EurekaInstanceTagsProvider eurekaInstanceTagProvider() {
+		return new DefaultEurekaInstanceTagsProvider();
+	}
+
+	@ConditionalOnMissingBean
+	@Bean
+	public EurekaInstanceMonitor eurekaInstanceMeterBinder(MeterRegistry meterRegistry,
+			PeerAwareInstanceRegistry instanceRegistry, EurekaInstanceTagsProvider tagProvider) {
+		return new EurekaInstanceMonitor(meterRegistry, instanceRegistry, tagProvider);
+	}
+
+}

spring-cloud-netflix-eureka-server/src/main/java/org/springframework/cloud/netflix/eureka/server/metrics/EurekaInstanceMonitor.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2013-2024 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.cloud.netflix.eureka.server.metrics;
+
+import java.util.Map;
+import java.util.Objects;
+import java.util.stream.Collectors;
+
+import com.netflix.eureka.registry.PeerAwareInstanceRegistry;
+import io.micrometer.core.instrument.MeterRegistry;
+import io.micrometer.core.instrument.MultiGauge;
+import io.micrometer.core.instrument.Tags;
+
+import org.springframework.cloud.netflix.eureka.server.event.EurekaInstanceCanceledEvent;
+import org.springframework.cloud.netflix.eureka.server.event.EurekaInstanceRegisteredEvent;
+import org.springframework.cloud.netflix.eureka.server.event.EurekaInstanceRenewedEvent;
+import org.springframework.context.ApplicationEvent;
+import org.springframework.context.event.SmartApplicationListener;
+
+/**
+ * {@link SmartApplicationListener} for collecting event metrics from
+ * {@link PeerAwareInstanceRegistry}.
+ *
+ * @author Wonchul Heo
+ * @since 4.1.2
+ */
+public class EurekaInstanceMonitor implements SmartApplicationListener {
+
+	private final MultiGauge eurekaInstances;
+
+	private final PeerAwareInstanceRegistry instanceRegistry;
+
+	private final EurekaInstanceTagsProvider tagProvider;
+
+	EurekaInstanceMonitor(MeterRegistry meterRegistry, PeerAwareInstanceRegistry instanceRegistry,
+			EurekaInstanceTagsProvider tagProvider) {
+		Objects.requireNonNull(meterRegistry);
+		this.instanceRegistry = Objects.requireNonNull(instanceRegistry);
+		this.tagProvider = Objects.requireNonNull(tagProvider);
+		this.eurekaInstances = MultiGauge.builder("eureka.server.instances")
+				.description("Number of application instances registered with the Eureka server.")
+				.register(meterRegistry);
+	}
+
+	@Override
+	public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
+		// If events that change state are added, an event class must be added.
+		return EurekaInstanceCanceledEvent.class.isAssignableFrom(eventType)
+				|| EurekaInstanceRegisteredEvent.class.isAssignableFrom(eventType)
+				|| EurekaInstanceRenewedEvent.class.isAssignableFrom(eventType);
+	}
+
+	@Override
+	public void onApplicationEvent(ApplicationEvent event) {
+		final Map<Tags, Long> aggregatedCounts = instanceRegistry.getApplications().getRegisteredApplications().stream()
+				.flatMap(application -> application.getInstances().stream())
+				.collect(Collectors.groupingBy(tagProvider::eurekaInstanceTags, Collectors.counting()));
+		eurekaInstances.register(aggregatedCounts.entrySet().stream()
+				.map(entry -> MultiGauge.Row.of(entry.getKey(), entry.getValue())).collect(Collectors.toList()), true);
+	}
+
+}

spring-cloud-netflix-eureka-server/src/main/java/org/springframework/cloud/netflix/eureka/server/metrics/EurekaInstanceTagsProvider.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2013-2024 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.cloud.netflix.eureka.server.metrics;
+
+import com.netflix.appinfo.InstanceInfo;
+import io.micrometer.core.instrument.Tags;
+
+/**
+ * Provides {@link Tags} for Eureka instance metrics.
+ *
+ * @author Wonchul Heo
+ * @since 4.1.2
+ */
+public interface EurekaInstanceTagsProvider {
+
+	Tags eurekaInstanceTags(InstanceInfo instanceInfo);
+
+}

spring-cloud-netflix-eureka-server/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -0,0 +1,10 @@
+{
+  "properties": [
+    {
+      "name": "eureka.server.metrics.enabled",
+      "type": "java.lang.Boolean",
+      "defaultValue": "false",
+      "description": "Indicates whether the metrics should be enabled for eureka instances."
+    }
+  ]
+}

spring-cloud-netflix-eureka-server/src/main/resources/META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports

@@ -1 +1,2 @@
-org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration
+org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration
+org.springframework.cloud.netflix.eureka.server.metrics.EurekaInstanceMetricsAutoConfiguration

spring-cloud-netflix-eureka-server/src/test/java/org/springframework/cloud/netflix/eureka/server/EurekaInstanceFixture.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2013-2024 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.cloud.netflix.eureka.server;
+
+import com.netflix.appinfo.InstanceInfo;
+import com.netflix.appinfo.LeaseInfo;
+
+public final class EurekaInstanceFixture {
+
+	private EurekaInstanceFixture() {
+	}
+
+	public static LeaseInfo getLeaseInfo() {
+		LeaseInfo.Builder leaseBuilder = LeaseInfo.Builder.newBuilder();
+		leaseBuilder.setRenewalIntervalInSecs(10);
+		leaseBuilder.setDurationInSecs(15);
+		return leaseBuilder.build();
+	}
+
+	public static InstanceInfo getInstanceInfo(String appName, String hostName, String instanceId, int port,
+			LeaseInfo leaseInfo) {
+		InstanceInfo.Builder builder = InstanceInfo.Builder.newBuilder();
+		builder.setAppName(appName);
+		builder.setHostName(hostName);
+		builder.setInstanceId(instanceId);
+		builder.setPort(port);
+		builder.setLeaseInfo(leaseInfo);
+		return builder.build();
+	}
+
+}