Add ServiceStatusMonitor to monitor service health

docs/configuration/index.md

@@ -399,6 +399,7 @@ Metric monitoring is an essential part of Druid operations.  The following monit
 |`org.apache.druid.server.metrics.TaskCountStatsMonitor`|Reports how many ingestion tasks are currently running/pending/waiting and also the number of successful/failed tasks per emission period.|
 |`org.apache.druid.server.metrics.TaskSlotCountStatsMonitor`|Reports metrics about task slot usage per emission period.|
 |`org.apache.druid.server.metrics.WorkerTaskCountStatsMonitor`|Reports how many ingestion tasks are currently running/pending/waiting, the number of successful/failed tasks, and metrics about task slot usage for the reporting worker, per emission period. Only supported by middleManager node types.|
+|`org.apache.druid.server.metrics.ServiceStatusMonitor`|Reports a heartbeat for the service.|
 
 For example, you might configure monitors on all processes for system and JVM information within `common.runtime.properties` as follows:
 

docs/operations/metrics.md

@@ -329,6 +329,12 @@ If `emitBalancingStats` is set to `true` in the Coordinator [dynamic configurati
 
 ## General Health
 
+### Service Health
+
+|Metric|Description|Dimensions|Normal Value|
+|------|-----------|----------|------------|
+| `service/heartbeat` | Metric indicating the service is up. `ServiceStatusMonitor` must be enabled. |`leader` on the Overlord and Coordinator.|1|
+
 ### Historical
 
 |Metric|Description|Dimensions|Normal Value|

server/src/main/java/org/apache/druid/server/metrics/ServiceStatusMonitor.java

@@ -0,0 +1,55 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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
+ *
+ *   http://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.apache.druid.server.metrics;
+
+import com.google.common.base.Supplier;
+import com.google.inject.Inject;
+import com.google.inject.name.Named;
+import org.apache.druid.java.util.emitter.service.ServiceEmitter;
+import org.apache.druid.java.util.emitter.service.ServiceMetricEvent;
+import org.apache.druid.java.util.metrics.AbstractMonitor;
+
+import java.util.Map;
+
+/**
+ * Reports a heartbeat for the service.
+ */
+public class ServiceStatusMonitor extends AbstractMonitor
+{
+
+  @Named("heartbeat")
+  @Inject(optional = true)
+  Supplier<Map<String, Object>> heartbeatTagsSupplier = null;
+
+  @Override
+  public boolean doMonitor(ServiceEmitter emitter)
+  {
+    final ServiceMetricEvent.Builder builder = new ServiceMetricEvent.Builder();
+    if (heartbeatTagsSupplier != null && heartbeatTagsSupplier.get() != null) {
+      heartbeatTagsSupplier.get().forEach((k, v) -> {
+        builder.setDimension(k, v);
+      });
+    }
+
+    emitter.emit(builder.build("service/heartbeat", 1));
+    return true;
+  }
+}
+

server/src/test/java/org/apache/druid/server/metrics/ServiceStatusMonitorTest.java

@@ -0,0 +1,82 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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
+ *
+ *   http://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.apache.druid.server.metrics;
+
+import com.google.common.base.Supplier;
+import org.apache.druid.java.util.metrics.StubServiceEmitter;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class ServiceStatusMonitorTest
+{
+
+  private ServiceStatusMonitor monitor;
+  private Map<String, Object> heartbeatTags;
+  private Supplier<Map<String, Object>> heartbeatTagsSupplier = () -> heartbeatTags;
+  private static String HEARTBEAT_METRIC_KEY = "service/heartbeat";
+
+  @Before
+  public void setUp()
+  {
+    monitor = new ServiceStatusMonitor();
+    heartbeatTags = new HashMap<>();
+    monitor.heartbeatTagsSupplier = heartbeatTagsSupplier;
+  }
+
+  @Test
+  public void testDefaultHeartbeatReported()
+  {
+    final StubServiceEmitter emitter = new StubServiceEmitter("service", "host");
+    monitor.doMonitor(emitter);
+    Assert.assertEquals(1, emitter.getEvents().size());
+    Assert.assertEquals(HEARTBEAT_METRIC_KEY, emitter.getEvents().get(0).toMap().get("metric"));
+    Assert.assertEquals(1, emitter.getEvents().get(0).toMap().get("value"));
+  }
+
+  @Test
+  public void testLeaderTag()
+  {
+    heartbeatTags.put("leader", 1);
+    final StubServiceEmitter emitter = new StubServiceEmitter("service", "host");
+    monitor.doMonitor(emitter);
+    Assert.assertEquals(1, emitter.getEvents().size());
+    Assert.assertEquals(1, emitter.getEvents().get(0).toMap().get("leader"));
+    Assert.assertEquals(HEARTBEAT_METRIC_KEY, emitter.getEvents().get(0).toMap().get("metric"));
+    Assert.assertEquals(1, emitter.getEvents().get(0).toMap().get("value"));
+  }
+
+  @Test
+  public void testMoreThanOneTag()
+  {
+    heartbeatTags.put("leader", 1);
+    heartbeatTags.put("taskRunner", "http");
+    final StubServiceEmitter emitter = new StubServiceEmitter("service", "host");
+    monitor.doMonitor(emitter);
+    Assert.assertEquals(1, emitter.getEvents().size());
+    Assert.assertEquals(1, emitter.getEvents().get(0).toMap().get("leader"));
+    Assert.assertEquals("http", emitter.getEvents().get(0).toMap().get("taskRunner"));
+    Assert.assertEquals(HEARTBEAT_METRIC_KEY, emitter.getEvents().get(0).toMap().get("metric"));
+    Assert.assertEquals(1, emitter.getEvents().get(0).toMap().get("value"));
+  }
+}

services/src/main/java/org/apache/druid/cli/CliCoordinator.java

@@ -24,13 +24,15 @@
 import com.github.rvesse.airline.annotations.Command;
 import com.google.common.base.Predicates;
 import com.google.common.base.Strings;
+import com.google.common.base.Supplier;
 import com.google.common.collect.ImmutableSet;
 import com.google.inject.Binder;
 import com.google.inject.Inject;
 import com.google.inject.Key;
 import com.google.inject.Module;
 import com.google.inject.Provider;
 import com.google.inject.Provides;
+import com.google.inject.TypeLiteral;
 import com.google.inject.name.Names;
 import com.google.inject.util.Providers;
 import org.apache.curator.framework.CuratorFramework;
@@ -119,8 +121,10 @@
 import org.joda.time.Duration;
 
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Properties;
 import java.util.Set;
 import java.util.concurrent.ExecutorService;
@@ -330,6 +334,10 @@ public void configure(Binder binder)
               binder.bind(TaskStorage.class).toProvider(Providers.of(null));
               binder.bind(TaskMaster.class).toProvider(Providers.of(null));
               binder.bind(RowIngestionMetersFactory.class).toProvider(Providers.of(null));
+              // Bind HeartbeatSupplier only when the service operates independently of Overlord.
+              binder.bind(new TypeLiteral<Supplier<Map<String, Object>>>() {})
+                  .annotatedWith(Names.named("heartbeat"))
+                  .toProvider(HeartbeatSupplier.class);
             }
 
             binder.bind(CoordinatorCustomDutyGroups.class)
@@ -459,4 +467,26 @@ public CoordinatorCustomDutyGroups get()
       }
     }
   }
+
+  private static class HeartbeatSupplier implements Provider<Supplier<Map<String, Object>>>
+  {
+    private final DruidCoordinator coordinator;
+
+    @Inject
+    public HeartbeatSupplier(DruidCoordinator coordinator)
+    {
+      this.coordinator = coordinator;
+    }
+
+    @Override
+    public Supplier<Map<String, Object>> get()
+    {
+      return () -> {
+        Map<String, Object> heartbeatTags = new HashMap<>();
+        heartbeatTags.put("leader", coordinator.isLeader() ? 1 : 0);
+
+        return heartbeatTags;
+      };
+    }
+  }
 }

services/src/main/java/org/apache/druid/cli/CliOverlord.java

@@ -21,6 +21,7 @@
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.github.rvesse.airline.annotations.Command;
+import com.google.common.base.Supplier;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.inject.Binder;
@@ -32,6 +33,7 @@
 import com.google.inject.TypeLiteral;
 import com.google.inject.multibindings.MapBinder;
 import com.google.inject.multibindings.Multibinder;
+import com.google.inject.name.Named;
 import com.google.inject.name.Names;
 import com.google.inject.servlet.GuiceFilter;
 import com.google.inject.util.Providers;
@@ -134,7 +136,9 @@
 import org.eclipse.jetty.servlet.ServletContextHandler;
 import org.eclipse.jetty.servlet.ServletHolder;
 
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.Properties;
 import java.util.Set;
 
@@ -354,6 +358,19 @@ public TaskStorageDirTracker getTaskStorageDirTracker(WorkerConfig workerConfig,
               {
                 return TaskStorageDirTracker.fromConfigs(workerConfig, taskConfig);
               }
+
+              @Provides
+              @LazySingleton
+              @Named("heartbeat")
+              public Supplier<Map<String, Object>> getHeartbeatSupplier(TaskMaster taskMaster)
+              {
+                return () -> {
+                  Map<String, Object> heartbeatTags = new HashMap<>();
+                  heartbeatTags.put("leader", taskMaster.isLeader() ? 1 : 0);
+
+                  return heartbeatTags;
+                };
+              }
             };
           }