Configurable routers, add query count based router

docs/operation.md

@@ -68,3 +68,21 @@ To gracefully shutdown a single worker process, see
 [this](https://trino.io/docs/current/admin/graceful-shutdown.html) for the
 operations.
 
+## 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,
+then use `QueryCountBasedRouter`, it can be configured by adding the module name 
+to config file's modules section like below
+```
+modules:
+  - io.trino.gateway.ha.module.HaGatewayProviderModule
+  - io.trino.gateway.ha.module.ClusterStateListenerModule
+  - io.trino.gateway.ha.module.ClusterStatsMonitorModule
+  - io.trino.gateway.ha.module.QueryCountBasedRouterProvider
+```
+- The router works on the stats it receives from the clusters about the load i.e number queries queued and running on a cluster at regular intervals which can be configured like below. The default interval is 1 min
+```
+monitor:
+  taskDelaySeconds: 10
+```

gateway-ha/gateway-ha-config.yml

@@ -32,6 +32,10 @@ server:
       port: 8091
       useForwardedHeaders: true
 
+# This can be adjusted based on the coordinator state
+monitor:
+  taskDelaySeconds: 10
+
 modules:
   - io.trino.gateway.ha.module.HaGatewayProviderModule
   - io.trino.gateway.ha.module.ClusterStateListenerModule

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

@@ -27,6 +27,8 @@
 import io.dropwizard.lifecycle.Managed;
 import io.dropwizard.lifecycle.setup.LifecycleEnvironment;
 import io.dropwizard.servlets.tasks.Task;
+import io.trino.gateway.ha.module.RouterBaseModule;
+import io.trino.gateway.ha.module.StochasticRoutingManagerProvider;
 import jakarta.ws.rs.Path;
 import jakarta.ws.rs.ext.Provider;
 import org.glassfish.jersey.server.filter.RolesAllowedDynamicFeature;
@@ -41,6 +43,7 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Optional;
 import java.util.Set;
 
 /**
@@ -66,6 +69,34 @@ public abstract class BaseApp<T extends AppConfiguration>
     private final ImmutableList.Builder<Module> appModules = ImmutableList.builder();
     private Injector injector;
 
+    private AppModule newModule(String clazz, T configuration, Environment environment)
+    {
+        try {
+            logger.info("Trying to load module [{}]", clazz);
+            Object module =
+                    Class.forName(clazz)
+                            .getConstructor(configuration.getClass(), Environment.class)
+                            .newInstance(configuration, environment);
+            return ((AppModule) module);
+        }
+        catch (Exception e) {
+            logger.error("Could not instantiate module [" + clazz + "]", e);
+            onFatalError(e);
+        }
+    }
+
+    private void validateModules(List<AppModule> modules, T configuration, Environment environment)
+    {
+        Optional<AppModule> routerProvider = modules.stream()
+                                        .filter(module -> module instanceof RouterBaseModule)
+                                        .findFirst();
+        if (routerProvider.isEmpty()) {
+            logger.warn("Router provider doesn't exist in the config, using the StochasticRoutingManagerProvider");
+            String clazz = StochasticRoutingManagerProvider.class.getCanonicalName();
+            modules.add(newModule(clazz, configuration, environment));
+        }
+    }
+
     protected BaseApp(String... basePackages)
     {
         final ConfigurationBuilder confBuilder = new ConfigurationBuilder();
@@ -171,18 +202,11 @@ protected List<AppModule> addModules(T configuration, Environment environment)
             return modules;
         }
         for (String clazz : configuration.getModules()) {
-            try {
-                logger.info("Trying to load module [{}]", clazz);
-                Object ob =
-                        Class.forName(clazz)
-                                .getConstructor(configuration.getClass(), Environment.class)
-                                .newInstance(configuration, environment);
-                modules.add((AppModule) ob);
-            }
-            catch (Exception e) {
-                logger.error("Could not instantiate module [" + clazz + "]", e);
-            }
+            modules.add(newModule(clazz, configuration, environment));
         }
+
+        validateModules(modules, configuration, environment);
+
         return modules;
     }
 

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

@@ -31,13 +31,14 @@
 public class ActiveClusterMonitor
         implements Managed
 {
-    public static final int MONITOR_TASK_DELAY_MIN = 1;
+    public static final int MONITOR_TASK_DELAY_SECONDS = 60;
     public static final int DEFAULT_THREAD_POOL_SIZE = 20;
     private static final Logger log = LoggerFactory.getLogger(ActiveClusterMonitor.class);
 
     private final List<TrinoClusterStatsObserver> clusterStatsObservers;
     private final GatewayBackendManager gatewayBackendManager;
-    private final int taskDelayMin;
+
+    private final int taskDelaySeconds;
     private final ClusterStatsMonitor clusterStatsMonitor;
     private volatile boolean monitorActive = true;
     private final ExecutorService executorService = Executors.newFixedThreadPool(DEFAULT_THREAD_POOL_SIZE);
@@ -52,9 +53,9 @@ public ActiveClusterMonitor(
     {
         this.clusterStatsObservers = clusterStatsObservers;
         this.gatewayBackendManager = gatewayBackendManager;
-        this.taskDelayMin = monitorConfiguration.getTaskDelayMin();
+        this.taskDelaySeconds = monitorConfiguration.getTaskDelaySeconds();
         this.clusterStatsMonitor = clusterStatsMonitor;
-        log.info("Running cluster monitor with task delay of {}", taskDelayMin);
+        log.info("Running cluster monitor with connection task delay of {} seconds", taskDelaySeconds);
     }
 
     /**
@@ -67,6 +68,7 @@ public void start()
                 () -> {
                     while (monitorActive) {
                         try {
+                            log.info("Getting the stats for the active clusters");
                             List<ProxyBackendConfiguration> activeClusters =
                                     gatewayBackendManager.getAllActiveBackends();
                             List<Future<ClusterStats>> futures = new ArrayList<>();
@@ -91,7 +93,7 @@ public void start()
                             log.error("Error performing backend monitor tasks", e);
                         }
                         try {
-                            Thread.sleep(TimeUnit.MINUTES.toMillis(taskDelayMin));
+                            Thread.sleep(TimeUnit.SECONDS.toMillis(taskDelaySeconds));
                         }
                         catch (Exception e) {
                             log.error("Error with monitor task", e);