org.apache.hadoop.net.DNSToSwitchMappingWithDependency Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
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* 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.Private
@InterfaceStability.Evolving
public interface DNSToSwitchMappingWithDependency extends DNSToSwitchMapping {
/**
* Get a list of dependent DNS-names for a given DNS-name/IP-address.
* Dependent DNS-names fall into the same fault domain which must be
* taken into account when placing replicas. This is intended to be used for
* cross node group dependencies when node groups are not sufficient to
* distinguish data nodes by fault domains. In practice, this is needed when
* a compute server runs VMs which use shared storage (as opposite to
* directly attached storage). In this case data nodes fall in two different
* fault domains. One fault domain is defined by a compute server and
* the other is defined by storage. With node groups we can group data nodes
* either by server fault domain or by storage fault domain. However one of
* the fault domains cannot be handled and there we need to define cross node
* group dependencies. These dependencies are applied in block placement
* polices which ensure that no two replicas will be on two dependent nodes.
* @param name - host name or IP address of a data node. Input host name
* parameter must take a value of dfs.datanode.hostname config value if this
* config property is set. Otherwise FQDN of the data node is used.
* @return list of dependent host names. If dfs.datanode.hostname config
* property is set, then its value must be returned.
* Otherwise, FQDN is returned.
*/
public List getDependency(String name);
}