/**
* 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.hdfs.server.namenode;
import org.apache.hadoop.classification.InterfaceAudience;
/**
* Implementers of this class represent a NN resource whose availability can be
* checked. A resource can be either "required" or "redundant". All required
* resources must be available for the NN to continue operating. The NN will
* continue to operate as long as *any* redundant resource is available.
*/
@InterfaceAudience.Private
interface CheckableNameNodeResource {
/**
* Is this resource currently available.
*
* @return true if and only if the resource in question is available.
*/
public boolean isResourceAvailable();
/**
* Is this resource required.
*
* @return true if and only if the resource in question is required for NN operation.
*/
public boolean isRequired();
}