Add health check API endpoints

docs/installation.md

@@ -347,7 +347,7 @@ Standard Helm options such as `replicaCount`, `image`, `imagePullSecrets`,
 More detail about the chart are available in the [values 
 reference documentation](https://github.com/trinodb/charts/blob/main/charts/gateway/README.md)
 
-### Health Checks
+### Health checks on Trino clusters
 
 The Trino Gateway periodically performs health checks and maintains
 an in-memory TrinoStatus for each backend. If a backend fails a health check,

docs/operation.md

@@ -36,6 +36,7 @@ documentation](https://trino.io/docs/current/admin/graceful-shutdown.html) for
 more details.
 
 ## Query routing options
+
 - The default router selects the backend randomly to route the queries. 
 - If you want to route the queries to the least loaded backend for a user
 i.e. backend with the least number of queries running or queued from a particular user,
@@ -65,3 +66,15 @@ scrape_configs:
     - targets:
         - gateway1.example.com:8080
 ```
+
+## Trino Gateway health endpoints
+
+Trino Gateway provides two API endpoints to indicate the current status of the server:
+
+* `/trino-gateway/livez` always returns status code 200, indicating the server is
+alive. However, it might not respond if the Trino Gateway is too busy, stuck, or
+taking a long time for garbage collection.
+* `/trino-gateway/readyz` returns status code 200, indicating the server has
+completed initialization and is ready to serve requests. This means the initial
+connection to the database and the first round of health check on Trino clusters
+are completed. Otherwise, status code 503 is returned.

gateway-ha/src/main/java/io/trino/gateway/baseapp/BaseApp.java

@@ -26,6 +26,7 @@
 import io.trino.gateway.ha.module.RouterBaseModule;
 import io.trino.gateway.ha.module.StochasticRoutingManagerProvider;
 import io.trino.gateway.ha.resource.EntityEditorResource;
+import io.trino.gateway.ha.resource.GatewayHealthCheckResource;
 import io.trino.gateway.ha.resource.GatewayResource;
 import io.trino.gateway.ha.resource.GatewayViewResource;
 import io.trino.gateway.ha.resource.GatewayWebAppResource;
@@ -179,6 +180,7 @@ private static void registerResources(Binder binder)
         jaxrsBinder(binder).bind(PublicResource.class);
         jaxrsBinder(binder).bind(TrinoResource.class);
         jaxrsBinder(binder).bind(WebUIStaticResource.class);
+        jaxrsBinder(binder).bind(GatewayHealthCheckResource.class);
     }
 
     private static void registerAuthFilters(Binder binder)

gateway-ha/src/main/java/io/trino/gateway/ha/clustermonitor/ActiveClusterMonitor.java

@@ -37,6 +37,7 @@ public class ActiveClusterMonitor
     public static final int DEFAULT_THREAD_POOL_SIZE = 20;
     private static final Logger log = Logger.get(ActiveClusterMonitor.class);
 
+    private volatile boolean isInitialized;
     private final List<TrinoClusterStatsObserver> clusterStatsObservers;
     private final GatewayBackendManager gatewayBackendManager;
 
@@ -83,6 +84,7 @@ public void start()
                         observer.observe(stats);
                     }
                 }
+                isInitialized = true;
             }
             catch (Exception e) {
                 log.error(e, "Error performing backend monitor tasks");
@@ -96,4 +98,9 @@ public void stop()
         executorService.shutdownNow();
         scheduledExecutor.shutdownNow();
     }
+
+    public boolean isInitialized()
+    {
+        return isInitialized;
+    }
 }

gateway-ha/src/main/java/io/trino/gateway/ha/resource/GatewayHealthCheckResource.java

@@ -0,0 +1,54 @@
+/*
+ * 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
+ *
+ *     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 io.trino.gateway.ha.resource;
+
+import com.google.inject.Inject;
+import io.trino.gateway.ha.clustermonitor.ActiveClusterMonitor;
+import jakarta.ws.rs.GET;
+import jakarta.ws.rs.Path;
+import jakarta.ws.rs.core.Response;
+
+import static java.util.Objects.requireNonNull;
+
+@Path("/trino-gateway")
+public class GatewayHealthCheckResource
+{
+    private final ActiveClusterMonitor activeClusterMonitor;
+
+    @Inject
+    public GatewayHealthCheckResource(ActiveClusterMonitor activeClusterMonitor)
+    {
+        this.activeClusterMonitor = requireNonNull(activeClusterMonitor, "activeClusterMonitor is null");
+    }
+
+    @GET
+    @Path("/livez")
+    public Response liveness()
+    {
+        return Response.ok("ok").build();
+    }
+
+    @GET
+    @Path("/readyz")
+    public Response readiness()
+    {
+        if (!activeClusterMonitor.isInitialized()) {
+            return Response
+                    .status(Response.Status.SERVICE_UNAVAILABLE)
+                    .entity("Trino Gateway is still initializing")
+                    .build();
+        }
+        return Response.ok("ok").build();
+    }
+}

gateway-ha/src/test/java/io/trino/gateway/ha/TestGatewayHaMultipleBackend.java

@@ -49,6 +49,7 @@
 import static com.google.common.collect.MoreCollectors.onlyElement;
 import static com.google.common.net.HttpHeaders.CONTENT_TYPE;
 import static com.google.common.net.MediaType.JSON_UTF_8;
+import static com.google.common.util.concurrent.Uninterruptibles.sleepUninterruptibly;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.testcontainers.utility.MountableFile.forClasspathResource;
 
@@ -362,6 +363,30 @@ void testCookieSigning()
         assertThat(callbackResponse.code()).isEqualTo(500);
     }
 
+    @Test
+    void testHealthCheckEndpoints()
+            throws IOException
+    {
+        Request livenessCheck = new Request.Builder()
+                        .url("http://localhost:" + routerPort + "/trino-gateway/livez")
+                        .build();
+        Response livenessResponse = httpClient.newCall(livenessCheck).execute();
+        assertThat(livenessResponse.code()).isEqualTo(200);
+
+        Request readinessCheck = new Request.Builder()
+                .url("http://localhost:" + routerPort + "/trino-gateway/readyz")
+                .build();
+        for (int i = 0; i < 100; i++) {
+            try (Response readinessResponse = httpClient.newCall(readinessCheck).execute()) {
+                if (readinessResponse.code() == 200) {
+                    return;
+                }
+            }
+            sleepUninterruptibly(100, TimeUnit.MILLISECONDS);
+        }
+        throw new IllegalStateException("Trino Gateway health check failed");
+    }
+
     @AfterAll
     void cleanup()
     {