Emit Netty event loop metrics provided by MicroMeter

core/src/main/java/com/linecorp/armeria/common/CommonPools.java

@@ -22,13 +22,16 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import com.google.common.annotations.VisibleForTesting;
+
 import com.linecorp.armeria.client.ClientFactoryBuilder;
 import com.linecorp.armeria.common.metric.MeterIdPrefix;
 import com.linecorp.armeria.common.metric.MoreMeterBinders;
 import com.linecorp.armeria.common.util.BlockingTaskExecutor;
 import com.linecorp.armeria.common.util.EventLoopGroups;
 import com.linecorp.armeria.server.ServerBuilder;
 
+import io.micrometer.core.instrument.binder.netty4.NettyEventExecutorMetrics;
 import io.netty.channel.EventLoopGroup;
 
 /**
@@ -45,11 +48,7 @@ public final class CommonPools {
             EventLoopGroups.newEventLoopGroup(Flags.numCommonWorkers(), "armeria-common-worker", true);
 
     static {
-        // Bind EventLoopMetrics for the common worker group.
-        MoreMeterBinders
-                .eventLoopMetrics(WORKER_GROUP, new MeterIdPrefix("armeria.netty.common"))
-                .bindTo(Flags.meterRegistry());
-
+        bindEventLoopMetricsForWorkerGroup(WORKER_GROUP);
         try {
             final Class<?> aClass = Class.forName("reactor.core.scheduler.Schedulers",
                                                   true, CommonPools.class.getClassLoader());
@@ -65,6 +64,18 @@ public final class CommonPools {
         }
     }
 
+    @VisibleForTesting
+    static void bindEventLoopMetricsForWorkerGroup(EventLoopGroup evGroup) {
+        // Bind EventLoopMetrics for the common worker group.
+        MoreMeterBinders
+                .eventLoopMetrics(evGroup, new MeterIdPrefix("armeria.netty.common"))
+                .bindTo(Flags.meterRegistry());
+        // Bind the common event loop metrics emitted automatically by micrometer.
+        // These metrics intentionally duplicate those emitted by EventLoopMetrics to preserve
+        // backward compatibility.
+        new NettyEventExecutorMetrics(evGroup).bindTo(Flags.meterRegistry());
+    }
+
     /**
      * Returns the default common blocking task {@link BlockingTaskExecutor} which is used for
      * potentially long-running tasks which may block I/O threads.

core/src/main/java/com/linecorp/armeria/common/metric/EventLoopMetrics.java

@@ -98,6 +98,7 @@ void remove(EventLoopGroup eventLoopGroup) {
             return result;
         }
 
+        @Deprecated // use the same metric with micrometer namespace instead
         double pendingTasks() {
             int result = 0;
             for (EventLoopGroup group : registry) {

core/src/test/java/com/linecorp/armeria/common/CommonPoolsTest.java

@@ -0,0 +1,50 @@
+/*
+ *  Copyright 2025 LINE Corporation
+ *
+ *  LINE Corporation licenses this file to you 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 com.linecorp.armeria.common;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+import com.linecorp.armeria.common.metric.MoreMeters;
+import com.linecorp.armeria.common.util.EventLoopGroups;
+
+import io.micrometer.core.instrument.binder.netty4.NettyMeters;
+import io.netty.channel.EventLoopGroup;
+
+public class CommonPoolsTest {
+    @Test
+    public void testEventLoopMetricsBinding() throws Exception {
+        final EventLoopGroup testGroup = EventLoopGroups.newEventLoopGroup(1);
+
+        try {
+            CommonPools.bindEventLoopMetricsForWorkerGroup(testGroup);
+
+            // verify that registry contains the newly added metrics
+            final Map<String, Double> registeredMeters = MoreMeters.measureAll(Flags.meterRegistry());
+            assertThat(registeredMeters.keySet()
+                                       .stream()
+                                       .anyMatch(key -> key.startsWith(
+                                               NettyMeters.EVENT_EXECUTOR_TASKS_PENDING.getName())))
+                    .isTrue();
+        } finally {
+            testGroup.shutdownNow();
+        }
+    }
+}