001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.master;
019
020import java.io.IOException;
021import org.apache.hadoop.conf.Configuration;
022import org.apache.hadoop.hbase.Server;
023import org.apache.hadoop.hbase.ServerName;
024import org.apache.hadoop.hbase.monitoring.MonitoredTask;
025import org.apache.hadoop.hbase.util.Threads;
026import org.apache.hadoop.hbase.zookeeper.MasterAddressTracker;
027import org.apache.hadoop.hbase.zookeeper.ZKWatcher;
028import org.apache.zookeeper.KeeperException;
029import org.slf4j.Logger;
030import org.slf4j.LoggerFactory;
031
032/**
033 * An implementation of HMaster that always runs as a stand by and never transitions to active.
034 */
035public class AlwaysStandByHMaster extends HMaster {
036  /**
037   * An implementation of ActiveMasterManager that never transitions it's master to active state. It
038   * always remains as a stand by master. With the master registry implementation (HBASE-18095) it
039   * is expected to have at least one active / standby master always running at any point in time
040   * since they serve as the gateway for client connections.
041   *
042   * With this implementation, tests can simulate the scenario of not having an active master yet
043   * the client connections to the cluster succeed.
044   */
045  private static class AlwaysStandByMasterManager extends ActiveMasterManager {
046    private static final Logger LOG =
047        LoggerFactory.getLogger(AlwaysStandByMasterManager.class);
048
049    AlwaysStandByMasterManager(ZKWatcher watcher, ServerName sn, Server master) {
050      super(watcher, sn, master);
051    }
052
053    /**
054     * An implementation that never transitions to an active master.
055     */
056    boolean blockUntilBecomingActiveMaster(int checkInterval, MonitoredTask startupStatus) {
057      while (!(master.isAborted() || master.isStopped())) {
058        startupStatus.setStatus("Forever looping to stay as a standby master.");
059        try {
060          activeMasterServerName = null;
061          try {
062            if (MasterAddressTracker.getMasterAddress(watcher) != null) {
063              clusterHasActiveMaster.set(true);
064            }
065            Threads.sleepWithoutInterrupt(100);
066          } catch (IOException e) {
067            // pass, we will get notified when some other active master creates the znode.
068          }
069        } catch (KeeperException e) {
070          master.abort("Received an unexpected KeeperException, aborting", e);
071          return false;
072        }
073        synchronized (this.clusterHasActiveMaster) {
074          while (clusterHasActiveMaster.get() && !master.isStopped()) {
075            try {
076              clusterHasActiveMaster.wait(checkInterval);
077            } catch (InterruptedException e) {
078              // We expect to be interrupted when a master dies,
079              //  will fall out if so
080              LOG.debug("Interrupted waiting for master to die", e);
081            }
082          }
083          if (clusterShutDown.get()) {
084            this.master.stop(
085                "Cluster went down before this master became active");
086          }
087        }
088      }
089      return false;
090    }
091  }
092
093  public AlwaysStandByHMaster(Configuration conf) throws IOException {
094    super(conf);
095  }
096
097  protected ActiveMasterManager createActiveMasterManager(
098      ZKWatcher zk, ServerName sn, org.apache.hadoop.hbase.Server server) {
099    return new AlwaysStandByMasterManager(zk, sn, server);
100  }
101}