/**
 * 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();

}