clintropolis commented on a change in pull request #8987: Adding support for 
autoscaling in GCE
URL: https://github.com/apache/druid/pull/8987#discussion_r378090407
 
 

 ##########
 File path: 
extensions-contrib/gce-extensions/src/main/java/org/apache/druid/indexing/overlord/autoscaling/gce/GCEAutoScaler.java
 ##########
 @@ -0,0 +1,496 @@
+/*
+ * 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.indexing.overlord.autoscaling.gce;
+
+import com.fasterxml.jackson.annotation.JacksonInject;
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonTypeName;
+import com.google.api.client.googleapis.auth.oauth2.GoogleCredential;
+import com.google.api.client.googleapis.javanet.GoogleNetHttpTransport;
+import com.google.api.client.http.HttpTransport;
+import com.google.api.client.json.JsonFactory;
+import com.google.api.client.json.jackson2.JacksonFactory;
+import com.google.api.services.compute.Compute;
+import com.google.api.services.compute.ComputeScopes;
+import com.google.api.services.compute.model.Instance;
+import 
com.google.api.services.compute.model.InstanceGroupManagersDeleteInstancesRequest;
+import 
com.google.api.services.compute.model.InstanceGroupManagersListManagedInstancesResponse;
+import com.google.api.services.compute.model.InstanceList;
+import com.google.api.services.compute.model.ManagedInstance;
+import com.google.api.services.compute.model.Operation;
+import com.google.common.net.InetAddresses;
+import org.apache.druid.indexing.overlord.autoscaling.AutoScaler;
+import org.apache.druid.indexing.overlord.autoscaling.AutoScalingData;
+import 
org.apache.druid.indexing.overlord.autoscaling.SimpleWorkerProvisioningConfig;
+import org.apache.druid.java.util.emitter.EmittingLogger;
+
+import java.io.IOException;
+import java.security.GeneralSecurityException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Locale;
+
+/**
+ * This module permits the autoscaling of the workers in GCE
+ *
+ * General notes:
+ * - The IPs are IPs as in Internet Protocol, and they look like 1.2.3.4
+ * - The IDs are the names of the instances of instances created, they look 
like prefix-abcd,
+ *   where the prefix is chosen by you and abcd is a suffix assigned by GCE
+ */
+@JsonTypeName("gce")
+public class GCEAutoScaler implements AutoScaler<GCEEnvironmentConfig>
+{
+  private static final EmittingLogger log = new 
EmittingLogger(GCEAutoScaler.class);
+
+  private final GCEEnvironmentConfig envConfig;
+  private final int minNumWorkers;
+  private final int maxNumWorkers;
+  private final SimpleWorkerProvisioningConfig config;  // For future use
+
+  private Compute cachedComputeService = null;
+
+  @JsonCreator
+  public GCEAutoScaler(
+          @JsonProperty("minNumWorkers") int minNumWorkers,
+          @JsonProperty("maxNumWorkers") int maxNumWorkers,
+          @JsonProperty("envConfig") GCEEnvironmentConfig envConfig,
+          @JacksonInject SimpleWorkerProvisioningConfig config
+  )
+  {
+    this.minNumWorkers = minNumWorkers;
+    this.maxNumWorkers = maxNumWorkers;
+    this.envConfig = envConfig;
+    this.config = config;
+  }
+
+  /**
+   * CAVEAT: this is meant to be used only for testing passing a mock version 
of Compute
+   */
+  public GCEAutoScaler(
+          int minNumWorkers,
+          int maxNumWorkers,
+          GCEEnvironmentConfig envConfig,
+          SimpleWorkerProvisioningConfig config,
+          Compute compute
+  )
+  {
+    this(minNumWorkers, maxNumWorkers, envConfig, config);
+    this.cachedComputeService = compute;
+  }
+
+  @Override
+  @JsonProperty
+  public int getMinNumWorkers()
+  {
+    return minNumWorkers;
+  }
+
+  @Override
+  @JsonProperty
+  public int getMaxNumWorkers()
+  {
+    return maxNumWorkers;
+  }
+
+  @Override
+  @JsonProperty
+  public GCEEnvironmentConfig getEnvConfig()
+  {
+    return envConfig;
+  }
+
+  private synchronized Compute createComputeService()
+      throws IOException, GeneralSecurityException, InterruptedException
+  {
+    final int max_retries = 5;
+    final long retries_interval = 5 * 1000; // 5 secs.
+
+    int retries = 0;
+    while (cachedComputeService == null && retries < max_retries) {
+      if (retries > 0) {
+        Thread.sleep(retries_interval);
+      }
+
+      log.info("Creating new ComputeService [%d/%d]", retries + 1, 
max_retries);
+
+      try {
+        HttpTransport httpTransport = 
GoogleNetHttpTransport.newTrustedTransport();
+        JsonFactory jsonFactory = JacksonFactory.getDefaultInstance();
+        GoogleCredential credential = GoogleCredential.getApplicationDefault(
+                httpTransport,
+                jsonFactory
+        );
+        if (credential.createScopedRequired()) {
+          List<String> scopes = new ArrayList<>();
+          scopes.add(ComputeScopes.CLOUD_PLATFORM);
+          scopes.add(ComputeScopes.COMPUTE);
+          credential = credential.createScoped(scopes);
+        }
+
+        if (credential.getClientAuthentication() != null) {
+          log.error("Not using a service account, terminating");
+          System.exit(1);
+        }
+
+        cachedComputeService = new Compute.Builder(httpTransport, jsonFactory, 
credential)
+                .setApplicationName("DruidAutoscaler")
+                .build();
+
+        retries++;
+      }
+      catch (Throwable e) {
+        log.error(e, "Got Exception in creating the ComputeService");
+        throw e;
+      }
+    }
+    return cachedComputeService;
+  }
+
+  // Used to wait for an operation to finish
+  private Operation.Error waitForOperationEnd(
+      Compute compute,
+      Operation operation) throws Exception
+  {
+    final long pollInterval = 5 * 1000;  // 5 sec
+
+    String status = operation.getStatus();
+    String opId = operation.getName();
+    while (operation != null && !"DONE".equals(status)) {
 
 Review comment:
   Is there any chance this could get stuck forever? (should it give up after a 
certain number of tries?)
   
   We have a `RetryUtils` which can repeat stuff stuff until a condition is 
satisfied and can do stuff like exponential backoff that might be worth using 
here instead of looping with a fixed thread sleep.

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