/*
 * 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.
 */
/**
 * Interface between the Application Master and ZooKeeper. Classes here manage two
 * registrations: Drillbits and the AM itself.
 * <p>
 * Drillbit registration is used to confirm that Drillbits have indeed come online.
 * If Drillbits fail to come online, then the AM concludes that somethign went wrong.
 * If Drilbits drop offline unexpectedly, the AM concludes that the Drillbit is sick
 * and restarts it.
 * <p>
 * The AM registry prevents two AMs from attempting to manage the same cluster.
 */

package org.apache.drill.yarn.zk;