Add subsystem health check to liveness checks

connectivity/service/src/main/resources/connectivity.conf

@@ -1137,6 +1137,9 @@ pekko {
       "pekko-contrib-mongodb-persistence-connection-snapshots"
     ]
   }
+  management.health-checks.liveness-checks {
+    subsystem-health = "org.eclipse.ditto.internal.utils.health.SubsystemHealthCheck"
+  }
 }
 
 include "ditto-protocol-subscriber.conf"

gateway/service/src/main/resources/gateway.conf

@@ -575,6 +575,10 @@ pekko {
   management.health-checks.readiness-checks {
     gateway-http-readiness = "org.eclipse.ditto.gateway.service.health.GatewayHttpReadinessCheck"
   }
+
+  management.health-checks.liveness-checks {
+    subsystem-health = "org.eclipse.ditto.internal.utils.health.SubsystemHealthCheck"
+  }
 }
 
 include "ditto-protocol-subscriber.conf"

internal/utils/health/pom.xml

@@ -70,6 +70,11 @@
             <artifactId>slf4j-simple</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.awaitility</groupId>
+            <artifactId>awaitility</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
 </project>

internal/utils/health/src/main/java/org/eclipse/ditto/internal/utils/health/SubsystemHealthCheck.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2024 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.eclipse.ditto.internal.utils.health;
+
+import java.time.Duration;
+import java.util.concurrent.CompletionStage;
+import java.util.function.Supplier;
+
+import org.apache.pekko.actor.ActorSelection;
+import org.apache.pekko.actor.ActorSystem;
+import org.apache.pekko.pattern.Patterns;
+
+/**
+ * Health check supplier for Pekko Management checking whether the root actor's health checking actor reports success.
+ * The health check will report failure if health checking actor replies with status DOWN or times out.
+ */
+public final class SubsystemHealthCheck implements Supplier<CompletionStage<Boolean>> {
+
+    /**
+     * The message to ask the health checking actor.
+     */
+    private static final RetrieveHealth RETRIEVE_HEALTH_ASK_MESSAGE = RetrieveHealth.newInstance();
+
+    /**
+     * Default timeout for waiting for response from health checking actor.
+     */
+    private static final Duration TIMEOUT = Duration.ofSeconds(30);
+
+    /**
+     * Health checking actor selection path.
+     */
+    private static final String HEALTH_CHECKING_ACTOR_PATH =
+            "/user/*Root/" + DefaultHealthCheckingActorFactory.ACTOR_NAME;
+
+    private final ActorSelection healthCheckingActor;
+    private final Duration timeout;
+
+    /**
+     * Constructs subsystem health check with default timeout.
+     *
+     * @param system actor system to check health of
+     */
+    public SubsystemHealthCheck(final ActorSystem system) {
+        this(system, TIMEOUT);
+    }
+
+    /**
+     * Constructs subsystem health check with custom timeout.
+     *
+     * @param system actor system to check health of
+     * @param timeout timeout
+     */
+    public SubsystemHealthCheck(final ActorSystem system, final Duration timeout) {
+        healthCheckingActor = system.actorSelection(HEALTH_CHECKING_ACTOR_PATH);
+        this.timeout = timeout;
+    }
+
+    @Override
+    public CompletionStage<Boolean> get() {
+        return Patterns.ask(healthCheckingActor, RETRIEVE_HEALTH_ASK_MESSAGE, timeout)
+                .handle((answer, throwable) -> answer instanceof StatusInfo statusInfo
+                        && statusInfo.getStatus() != StatusInfo.Status.DOWN);
+    }
+
+}

internal/utils/health/src/test/java/org/eclipse/ditto/internal/utils/health/SubsystemHealthCheckTest.java

@@ -0,0 +1,159 @@
+/*
+ * Copyright (c) 2024 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.eclipse.ditto.internal.utils.health;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.time.Duration;
+
+import org.apache.pekko.actor.AbstractActor;
+import org.apache.pekko.actor.ActorRef;
+import org.apache.pekko.actor.ActorSystem;
+import org.apache.pekko.actor.Props;
+import org.apache.pekko.japi.pf.ReceiveBuilder;
+import org.apache.pekko.testkit.javadsl.TestKit;
+import org.awaitility.Awaitility;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+public class SubsystemHealthCheckTest {
+
+    private static final String TEST_ACTOR_READY = "ready";
+    private static final Duration HEALTH_CHECK_TIMEOUT = Duration.ofMillis(500);
+
+    /**
+     * Name of root actor in tests. Must end with "Root" to be recognized by {@link SubsystemHealthCheck}.
+     */
+    private static final String ROOT_ACTOR_NAME = "testRoot";
+
+    private ActorSystem actorSystem;
+    private SubsystemHealthCheck subsystemHealthCheck;
+
+    @Before
+    public void setUp() {
+        actorSystem = ActorSystem.create();
+        subsystemHealthCheck = new SubsystemHealthCheck(actorSystem, HEALTH_CHECK_TIMEOUT);
+    }
+
+    @After
+    public void tearDown() {
+        if (actorSystem != null) {
+            actorSystem.terminate();
+        }
+    }
+
+    @Test
+    public void testCheckReturnsTrueWhenHealthCheckingActorReturnsUp() {
+        new TestKit(actorSystem) {{
+            final var statusInfo = StatusInfo.fromStatus(StatusInfo.Status.UP);
+            actorSystem.actorOf(TestRootActor.props(statusInfo, getRef()), ROOT_ACTOR_NAME);
+
+            expectMsg(TEST_ACTOR_READY);
+
+            assertHealthCheckResult(subsystemHealthCheck, true);
+        }};
+    }
+
+    @Test
+    public void testCheckReturnsTrueWhenHealthCheckingActorReturnsUnknown() {
+        new TestKit(actorSystem) {{
+            final var statusInfo = StatusInfo.fromStatus(StatusInfo.Status.UNKNOWN);
+            actorSystem.actorOf(TestRootActor.props(statusInfo, getRef()), ROOT_ACTOR_NAME);
+
+            expectMsg(TEST_ACTOR_READY);
+
+            assertHealthCheckResult(subsystemHealthCheck, true);
+        }};
+    }
+
+    @Test
+    public void testCheckReturnsFalseWhenHealthCheckingActorReturnsDown() {
+        new TestKit(actorSystem) {{
+            final var statusInfo = StatusInfo.fromStatus(StatusInfo.Status.DOWN);
+            actorSystem.actorOf(TestRootActor.props(statusInfo, getRef()), ROOT_ACTOR_NAME);
+
+            expectMsg(TEST_ACTOR_READY);
+
+            assertHealthCheckResult(subsystemHealthCheck, false);
+        }};
+    }
+
+    @Test
+    public void testCheckReturnsFalseWhenHealthCheckingActorDoesNotExist() {
+        new TestKit(actorSystem) {{
+            assertHealthCheckResult(subsystemHealthCheck, false);
+        }};
+    }
+
+    private static void assertHealthCheckResult(SubsystemHealthCheck subsystemHealthCheck, boolean expected) {
+        final var healthCheckResultFuture = subsystemHealthCheck.get();
+        Awaitility.await()
+                .atMost(Duration.ofNanos(2 * HEALTH_CHECK_TIMEOUT.toNanos()))
+                .until(() -> healthCheckResultFuture.toCompletableFuture().isDone());
+        assertThat(healthCheckResultFuture.toCompletableFuture())
+                .isCompletedWithValue(expected);
+    }
+
+    private static class TestRootActor extends AbstractActor {
+
+        private TestRootActor(final StatusInfo statusInfo, final ActorRef actorToNotify) {
+            getContext().actorOf(TestHealthCheckingActor.props(statusInfo, actorToNotify),
+                    DefaultHealthCheckingActorFactory.ACTOR_NAME);
+        }
+
+        public static Props props(final StatusInfo statusInfo, final ActorRef actorToNotify) {
+            return Props.create(TestRootActor.class, statusInfo, actorToNotify);
+        }
+
+        @Override
+        public Receive createReceive() {
+            return ReceiveBuilder.create()
+                    .matchAny(this::unhandled)
+                    .build();
+        }
+
+    }
+
+    private static class TestHealthCheckingActor extends AbstractActor {
+
+        private final StatusInfo statusInfo;
+        private final ActorRef actorToNotify;
+
+        private TestHealthCheckingActor(final StatusInfo statusInfo, final ActorRef actorToNotify) {
+            this.statusInfo = statusInfo;
+            this.actorToNotify = actorToNotify;
+        }
+
+        public static Props props(final StatusInfo statusInfo, final ActorRef actorToNotify) {
+            return Props.create(TestHealthCheckingActor.class, statusInfo, actorToNotify);
+        }
+
+        @Override
+        public Receive createReceive() {
+            return ReceiveBuilder.create()
+                    .match(RetrieveHealth.class, this::returnStatusInfo)
+                    .build();
+        }
+
+        @Override
+        public void preStart() {
+            actorToNotify.tell(TEST_ACTOR_READY, getSelf());
+        }
+
+        private void returnStatusInfo(final RetrieveHealth command) {
+            getSender().tell(this.statusInfo, getSelf());
+        }
+    }
+
+}

policies/service/src/main/resources/policies.conf

@@ -231,6 +231,10 @@ pekko {
       "pekko-contrib-mongodb-persistence-policies-snapshots"
     ]
   }
+
+  management.health-checks.liveness-checks {
+    subsystem-health = "org.eclipse.ditto.internal.utils.health.SubsystemHealthCheck"
+  }
 }
 
 pekko-contrib-mongodb-persistence-policies-journal {

things/service/src/main/resources/things.conf

@@ -273,6 +273,10 @@ pekko {
     ]
   }
 
+  management.health-checks.liveness-checks {
+    subsystem-health = "org.eclipse.ditto.internal.utils.health.SubsystemHealthCheck"
+  }
+
 }
 
 pekko-contrib-mongodb-persistence-things-journal {

thingsearch/service/src/main/resources/search.conf

@@ -340,6 +340,10 @@ pekko {
       "blocked-namespaces-aware",
     ]
   }
+
+  management.health-checks.liveness-checks {
+    subsystem-health = "org.eclipse.ditto.internal.utils.health.SubsystemHealthCheck"
+  }
 }
 
 search-dispatcher {