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Subject [GitHub] vjagadish1989 commented on a change in pull request #903: SEP-19: Allocator changes for standby-aware container allocation, and active container failover
Date Wed, 27 Feb 2019 19:37:26 GMT
vjagadish1989 commented on a change in pull request #903: SEP-19: Allocator changes for standby-aware
container allocation, and active container failover
URL: https://github.com/apache/samza/pull/903#discussion_r260894484
 
 

 ##########
 File path: samza-core/src/main/java/org/apache/samza/clustermanager/StandbyContainerManager.java
 ##########
 @@ -0,0 +1,466 @@
+/*
+ * 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.samza.clustermanager;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.concurrent.ConcurrentHashMap;
+import org.apache.samza.job.model.JobModel;
+import org.apache.samza.storage.kv.Entry;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * Encapsulates logic and state concerning standby-containers.
+ */
+public class StandbyContainerManager {
+
+  private static final Logger log = LoggerFactory.getLogger(StandbyContainerManager.class);
+
+  private final SamzaApplicationState samzaApplicationState;
+
+  // Map of samza containerIDs to their corresponding active and standby containers, e.g.,
0 -> {0-0, 0-1}, 0-0 -> {0, 0-1}
+  // This is used for checking no two standbys or active-standby-pair are started on the
same host
+  private final Map<String, List<String>> standbyContainerConstraints;
+
+  // Map of active containers that are in failover, indexed by the active container's resourceID
(at the time of failure)
+  private final Map<String, FailoverMetadata> failovers;
+
+  // Resource-manager, used to stop containers
+  private ClusterResourceManager clusterResourceManager;
+
+  public StandbyContainerManager(SamzaApplicationState samzaApplicationState,
+      ClusterResourceManager clusterResourceManager) {
+    this.failovers = new ConcurrentHashMap<>();
+    this.standbyContainerConstraints = new HashMap<>();
+    this.samzaApplicationState = samzaApplicationState;
+    JobModel jobModel = samzaApplicationState.jobModelManager.jobModel();
+
+    // populate the standbyContainerConstraints map by iterating over all containers
+    jobModel.getContainers()
+        .keySet()
+        .forEach(containerId -> standbyContainerConstraints.put(containerId,
+            StandbyTaskUtil.getStandbyContainerConstraints(containerId, jobModel)));
+    this.clusterResourceManager = clusterResourceManager;
+
+    log.info("Populated standbyContainerConstraints map {}", standbyContainerConstraints);
+  }
+
+  /**
+   * We handle the stopping of a container depending on the case which is decided using the
exit-status:
+   *    Case 1. an Active-Container which has stopped for an "unknown" reason, then we start
it on the given preferredHost
+   *    Case 2. Active container has stopped because of node failure, thene we initiate a
failover
+   *    Case 3. StandbyContainer has stopped after it was chosen for failover, see {@link
StandbyContainerManager#handleStandbyContainerStop}
+   *    Case 4. StandbyContainer has stopped but not because of a failover, see {@link StandbyContainerManager#handleStandbyContainerStop}
+   *
+   * @param containerID containerID of the stopped container
+   * @param resourceID last resourceID of the stopped container
+   * @param preferredHost the host on which the container was running
+   * @param exitStatus the exit status of the failed container
+   * @param containerAllocator the container allocator
+   */
+  public void handleContainerStop(String containerID, String resourceID, String preferredHost,
int exitStatus,
+      AbstractContainerAllocator containerAllocator) {
+
+    if (StandbyTaskUtil.isStandbyContainer(containerID)) {
+      handleStandbyContainerStop(containerID, resourceID, preferredHost, containerAllocator);
+    } else {
+      // initiate failover for the active container based on the exitStatus
+      switch (exitStatus) {
+        case SamzaResourceStatus.DISK_FAIL:
+        case SamzaResourceStatus.ABORTED:
+        case SamzaResourceStatus.PREEMPTED:
+          initiateActiveContainerFailover(containerID, resourceID, containerAllocator);
+          break;
+      // in all other cases, request resource for the failed container
+        default:
+          log.info("Requesting resource for active-container {} on host {}", containerID,
preferredHost);
+          containerAllocator.requestResource(containerID, preferredHost);
+          break;
+      }
+    }
+  }
+
+  /**
+   * Handle the failed launch of a container, based on
+   *    Case 1. If it is an active container, then initiate a failover for it.
+   *    Case 2. If it is standby container, request a new resource on AnyHost.
+   * @param containerID the ID of the container that has failed
+   */
+  public void handleContainerLaunchFail(String containerID, String resourceID,
+      AbstractContainerAllocator containerAllocator) {
+
+    if (StandbyTaskUtil.isStandbyContainer(containerID)) {
+      log.info("Handling launch fail for standby-container {}, requesting resource on any
host {}", containerID);
+      containerAllocator.requestResource(containerID, ResourceRequestState.ANY_HOST);
+    } else {
+      initiateActiveContainerFailover(containerID, resourceID, containerAllocator);
+    }
+  }
+
+  /**
+   *  If a standby container has stopped, then there are two possible cases
+   *    Case 1. during a failover, the standby container was stopped for an active's start,
then we
+   *       1. request a resource on the standby's host to place the activeContainer, and
+   *       2. request anyhost to place this standby
+   *
+   *    Case 2. independent of a failover, the standby container stopped, in which proceed
with its resource-request
+   * @param standbyContainerID SamzaContainerID of the standby container
+   * @param preferredHost Preferred host of the standby container
+   */
+  private void handleStandbyContainerStop(String standbyContainerID, String resourceID, String
preferredHost,
+      AbstractContainerAllocator containerAllocator) {
+
+    // if this standbyContainerResource was stopped for a failover, we will find a metadata
entry
+    Optional<StandbyContainerManager.FailoverMetadata> failoverMetadata = this.checkIfUsedForFailover(resourceID);
+
+    if (failoverMetadata.isPresent()) {
+      String activeContainerID = failoverMetadata.get().activeContainerID;
+      String standbyContainerHostname = failoverMetadata.get().getStandbyContainerHostname(resourceID);
+
+      log.info("Requesting resource for active container {} on host {}, and backup container
{} on any host",
+          activeContainerID, standbyContainerHostname, standbyContainerID);
+
+      containerAllocator.requestResource(activeContainerID,
+          standbyContainerHostname); // request standbycontainer's host for active-container
+      containerAllocator.requestResource(standbyContainerID,
+          ResourceRequestState.ANY_HOST); // request anyhost for standby container
+      return;
+    } else {
+      log.info("Issuing request for standby container {} on host {}, since this is not for
a failover",
+          standbyContainerID, preferredHost);
+      containerAllocator.requestResource(standbyContainerID, preferredHost);
+      return;
+    }
+  }
+
+  /** Method to handle failover for a container.
+   *  If it is an active container,
+   *  We try to find a standby for the active container, and issue a stop on it.
+   *  If we do not find a standby container, we simply issue an anyhost request to place
it.
+   *  If it is standby container, we simply forward the request to the containerAllocator
+   *
+   * @param containerID the samzaContainerID of the active-container
+   * @param resourceID  the samza-resource-ID of the container when it failed (used to index
failover-state)
+   */
+  private void initiateActiveContainerFailover(String containerID, String resourceID,
+      AbstractContainerAllocator containerAllocator) {
+    Optional<Entry<String, SamzaResource>> standbyContainer = this.selectStandby(containerID,
resourceID);
+
+    // If we find a standbyContainer, we initiate a failover
+    if (standbyContainer.isPresent()) {
+
+      // ResourceID of the active container at the time of its last failure
+      String standbyContainerId = standbyContainer.get().getKey();
+      SamzaResource standbyResource = standbyContainer.get().getValue();
+      String standbyResourceID = standbyResource.getResourceID();
+      String standbyHost = standbyResource.getHost();
+
+      // update the failover state
+      this.registerFailover(containerID, resourceID, standbyResourceID, standbyHost);
+      log.info("Initiating failover and stopping standby container, found standbyContainer
{} = resource {}, "
+          + "for active container {}", standbyContainerId, standbyResourceID, containerID);
+      samzaApplicationState.failoversToStandby.incrementAndGet();
+
+      this.clusterResourceManager.stopStreamProcessor(standbyResource);
+      return;
 
 Review comment:
   "no returns" anywhere

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