hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/DNSToSwitchMapping.java

/**
 * 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.hadoop.net;

import java.util.List;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;

/**
 * An interface that must be implemented to allow pluggable
 * DNS-name/IP-address to RackID resolvers.
 *
 */
@InterfaceAudience.Public
@InterfaceStability.Evolving
public interface DNSToSwitchMapping {
  /**
   * Resolves a list of DNS-names/IP-addresses and returns back a list of
   * switch information (network paths). One-to-one correspondence must be 
   * maintained between the elements in the lists. 
   * Consider an element in the argument list - x.y.com. The switch information
   * that is returned must be a network path of the form /foo/rack, 
   * where / is the root, and 'foo' is the switch where 'rack' is connected.
   * Note the hostname/ip-address is not part of the returned path.
   * The network topology of the cluster would determine the number of
   * components in the network path.
   * <p/>
   *
   * If a name cannot be resolved to a rack, the implementation
   * should return {@link NetworkTopology#DEFAULT_RACK}. This
   * is what the bundled implementations do, though it is not a formal requirement
   *
   * @param names the list of hosts to resolve (can be empty)
   * @return list of resolved network paths.
   * If <i>names</i> is empty, the returned list is also empty
   */
  public List<String> resolve(List<String> names);

  /**
   * Reload all of the cached mappings.
   *
   * If there is a cache, this method will clear it, so that future accesses
   * will get a chance to see the new data.
   */
  public void reloadCachedMappings();
  
  /**
   * Reload cached mappings on specific nodes.
   *
   * If there is a cache on these nodes, this method will clear it, so that 
   * future accesses will see updated data.
   */
  public void reloadCachedMappings(List<String> names);
}