Collect metrics for application instances

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

@@ -615,6 +615,18 @@ 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
+
+Starting with version 4.1.1, `MultuGuage` listens events related to Eureka instances and creates and updates Eureka instance information in the metrics registry. By default, this setting is disabled, if you want to enable it, you need to change `eureka.instance.metrics.enabled` to `true`.
+
+The multi-gauge is named `eureka.server.instance.status`     and has the following tags (value are merged based on tags)
+
+- `application`: application name
+
+- `status`: instance status
+
+You can add additional tags by implementing `EurekaInstanceTagsProvider` separately. However, status is added separately because it is always needed.
+
 == 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 +1,36 @@
+/*
+ * 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 4.1.1
+ */
+class DefaultEurekaInstanceTagsProvider implements EurekaInstanceTagsProvider {
+
+	@Override
+	public Tags eurekaInstanceTags(InstanceInfo instanceInfo) {
+		return Tags.of(Tag.of("application", instanceInfo.getAppName()));
+	}
+
+}

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 4.1.1
+ */
+@ConditionalOnClass(MeterRegistry.class)
+@ConditionalOnBean(MeterRegistry.class)
+@AutoConfigureAfter({ MetricsAutoConfiguration.class, CompositeMeterRegistryAutoConfiguration.class,
+		EurekaServerAutoConfiguration.class })
+@ConditionalOnProperty(name = "eureka.instance.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 +1,80 @@
+/*
+ * 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.appinfo.InstanceInfo;
+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 4.1.1
+ */
+public class EurekaInstanceMonitor implements SmartApplicationListener {
+
+	private final MultiGauge eurekaInstanceStatuses;
+
+	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.eurekaInstanceStatuses = MultiGauge.builder("eureka.server.instance.status")
+				.description("Status of application instances registered with the Eureka server.")
+				.register(meterRegistry);
+	}
+
+	@Override
+	public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
+		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(this::tags, Collectors.counting()));
+		eurekaInstanceStatuses.register(aggregatedCounts.entrySet().stream()
+				.map(it -> MultiGauge.Row.of(it.getKey(), it.getValue())).collect(Collectors.toList()), true);
+	}
+
+	private Tags tags(InstanceInfo instanceInfo) {
+		return tagProvider.eurekaInstanceTags(instanceInfo).and("status", instanceInfo.getStatus().name());
+	}
+
+}

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

@@ -0,0 +1,33 @@
+/*
+ * 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;
+
+/**
+ * Provides {@link Tag Tags} for Eureka instance metrics.
+ *
+ * @author Wonchul Heo
+ * @since 4.1.1
+ */
+public interface EurekaInstanceTagsProvider {
+
+	Tags eurekaInstanceTags(InstanceInfo instanceInfo);
+
+}

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/EurekaInstanceMonitorTests.java

@@ -0,0 +1,154 @@
+/*
+ * 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 java.util.Map;
+import java.util.stream.Collectors;
+
+import com.netflix.appinfo.InstanceInfo;
+import io.micrometer.core.instrument.MeterRegistry;
+import io.micrometer.core.instrument.Tag;
+import io.micrometer.core.instrument.Tags;
+import io.micrometer.core.instrument.search.MeterNotFoundException;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.context.annotation.Configuration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.springframework.cloud.netflix.eureka.server.FixtureEurekaInstances.getInstanceInfo;
+import static org.springframework.cloud.netflix.eureka.server.FixtureEurekaInstances.getLeaseInfo;
+
+/**
+ * @author Wonchul Heo
+ */
+@SpringBootTest(classes = EurekaInstanceMonitorTests.Application.class,
+		webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT,
+		value = { "spring.application.name=eureka", "eureka.instance.metrics.enabled=true" })
+class EurekaInstanceMonitorTests {
+
+	private static final String APP_NAME = "MY-APP-NAME";
+
+	@Autowired
+	private InstanceRegistry instanceRegistry;
+
+	@Autowired
+	private MeterRegistry meterRegistry;
+
+	private InstanceInfo instanceInfo;
+
+	private InstanceInfo instanceInfo2;
+
+	@BeforeEach
+	void setup() {
+		this.instanceRegistry.clearRegistry();
+		this.meterRegistry.clear();
+		this.instanceInfo = getInstanceInfo(APP_NAME, "my-host-name", "my-host-name:8008", 8008, getLeaseInfo());
+		this.instanceInfo2 = getInstanceInfo(APP_NAME, "my-host-name", "my-host-name:8009", 8009, getLeaseInfo());
+	}
+
+	@Test
+	void testNoRegistration() {
+		assertThatThrownBy(() -> {
+			meterRegistry.get("eureka.server.instance.status").meter();
+		}).isInstanceOf(MeterNotFoundException.class);
+	}
+
+	@Test
+	void testMultipleRegistrations() {
+		instanceRegistry.register(instanceInfo, false);
+		instanceRegistry.register(instanceInfo2, false);
+
+		final Map<Tags, Long> counts = Map.of(tags(instanceInfo), 2L);
+		assertEurekaInstance(counts, counts);
+	}
+
+	@Test
+	void testPartialDeregistrationAfterMultipleRegistrations() {
+		instanceRegistry.register(instanceInfo, false);
+		instanceRegistry.register(instanceInfo2, false);
+		instanceRegistry.internalCancel(instanceInfo.getAppName(), instanceInfo.getInstanceId(), false);
+
+		final Map<Tags, Long> counts = Map.of(tags(instanceInfo), 1L);
+		assertEurekaInstance(counts, counts);
+	}
+
+	@Test
+	void testPartialDeregistrationAndThenRegistrationAfterMultipleRegistrations() {
+		instanceRegistry.register(instanceInfo, false);
+		instanceRegistry.register(instanceInfo2, false);
+		instanceRegistry.internalCancel(instanceInfo.getAppName(), instanceInfo.getInstanceId(), false);
+		instanceRegistry.register(instanceInfo, false);
+
+		final Map<Tags, Long> counts = Map.of(tags(instanceInfo), 2L);
+		assertEurekaInstance(counts, counts);
+	}
+
+	@Test
+	void testPartialNonRenewalAfterMultipleRegistrations() {
+		instanceRegistry.register(instanceInfo, false);
+		instanceRegistry.register(instanceInfo2, false);
+
+		instanceRegistry.statusUpdate(instanceInfo.getAppName(), instanceInfo.getInstanceId(),
+				InstanceInfo.InstanceStatus.DOWN, null, false);
+
+		final Map<Tags, Long> instanceRegistryCounts = Map.of(tags(instanceInfo), 1L, tags(instanceInfo2), 1L);
+		final Map<Tags, Long> meterRegistryCounts = Map.of(tags(instanceInfo2), 2L);
+		assertEurekaInstance(instanceRegistryCounts, meterRegistryCounts);
+	}
+
+	@Test
+	void testPartialRenewalAfterMultipleRegistrations() {
+		instanceRegistry.register(instanceInfo, false);
+		instanceRegistry.register(instanceInfo2, false);
+
+		instanceRegistry.statusUpdate(instanceInfo.getAppName(), instanceInfo.getInstanceId(),
+				InstanceInfo.InstanceStatus.DOWN, null, false);
+		instanceRegistry.renew(instanceInfo.getAppName(), instanceInfo.getInstanceId(), false);
+
+		final Map<Tags, Long> counts = Map.of(tags(instanceInfo), 1L, tags(instanceInfo2), 1L);
+		assertEurekaInstance(counts, counts);
+	}
+
+	private static Tags tags(InstanceInfo instanceInfo) {
+		return Tags.of(Tag.of("application", instanceInfo.getAppName()),
+				Tag.of("status", instanceInfo.getStatus().name()));
+	}
+
+	private void assertEurekaInstance(Map<Tags, Long> instanceRegistryCounts, Map<Tags, Long> meterRegistryCounts) {
+		final Map<Tags, Long> actualInstanceRegistryCounts = instanceRegistry.getApplications()
+				.getRegisteredApplications().stream().flatMap(application -> application.getInstances().stream())
+				.collect(Collectors.groupingBy(EurekaInstanceMonitorTests::tags, Collectors.counting()));
+		assertThat(actualInstanceRegistryCounts).isEqualTo(instanceRegistryCounts);
+
+		meterRegistryCounts.forEach((tags, count) -> {
+			assertThat((long) meterRegistry.get("eureka.server.instance.status").tags(tags).gauge().value())
+					.isEqualTo(count);
+		});
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	@EnableAutoConfiguration
+	@EnableEurekaServer
+	protected static class Application {
+
+	}
+}