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.util.ArrayList;
021import java.util.Collections;
022import java.util.List;
023import org.apache.hadoop.conf.Configuration;
024import org.apache.hadoop.hbase.ServerName;
025import org.apache.hadoop.hbase.util.ReflectionUtils;
026import org.apache.hadoop.net.DNSToSwitchMapping;
027import org.apache.hadoop.net.ScriptBasedMapping;
028import org.apache.yetus.audience.InterfaceAudience;
029
030/**
031 * Wrapper over the rack resolution utility in Hadoop. The rack resolution utility in Hadoop does
032 * resolution from hosts to the racks they belong to.
033 */
034@InterfaceAudience.Private
035public class RackManager {
036  public static final String UNKNOWN_RACK = "Unknown Rack";
037
038  private DNSToSwitchMapping switchMapping;
039
040  public RackManager() {
041  }
042
043  public RackManager(Configuration conf) {
044    switchMapping = ReflectionUtils.instantiateWithCustomCtor(
045      conf.getClass("hbase.util.ip.to.rack.determiner", ScriptBasedMapping.class,
046        DNSToSwitchMapping.class).getName(),
047      new Class<?>[] { Configuration.class }, new Object[] { conf });
048  }
049
050  /**
051   * Get the name of the rack containing a server, according to the DNS to switch mapping.
052   * @param server the server for which to get the rack name
053   * @return the rack name of the server
054   */
055  public String getRack(ServerName server) {
056    if (server == null) {
057      return UNKNOWN_RACK;
058    }
059    // just a note - switchMapping caches results (at least the implementation should unless the
060    // resolution is really a lightweight process)
061    List<String> racks = switchMapping.resolve(Collections.singletonList(server.getHostname()));
062    if (racks != null && !racks.isEmpty()) {
063      return racks.get(0);
064    }
065
066    return UNKNOWN_RACK;
067  }
068
069  /**
070   * Same as {@link #getRack(ServerName)} except that a list is passed
071   * @param servers list of servers we're requesting racks information for
072   * @return list of racks for the given list of servers
073   */
074  public List<String> getRack(List<ServerName> servers) {
075    // just a note - switchMapping caches results (at least the implementation should unless the
076    // resolution is really a lightweight process)
077    List<String> serversAsString = new ArrayList<>(servers.size());
078    for (ServerName server : servers) {
079      serversAsString.add(server.getHostname());
080    }
081    List<String> racks = switchMapping.resolve(serversAsString);
082    return racks;
083  }
084}