/**
* 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();
}