hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/health/HealthCheck.java

/*
 * 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.hdds.scm.container.replication.health;

import org.apache.hadoop.hdds.scm.container.replication.ContainerCheckRequest;

/**
 * Interface used by Container Health Check Handlers.
 */
public interface HealthCheck {

  /**
   * Handle the container and apply the given check to it. This may result in
   * commands getting generated to correct container states, or nothing
   * happening if the container is healthy.
   * @param request ContainerCheckRequest object representing the container
   * @return True if the request was handled or false if it was not and should
   *         be handled by the next handler in the chain.
   */
  boolean handle(ContainerCheckRequest request);

  /**
   * Starting from this HealthCheck, call the handle method. If it returns
   * false, indicating the request was not handled, then forward the request to
   * the next handler in the chain via its handleChain method. Repeating until
   * the request is handled, or there are no further handlers to try.
   * @param request
   * @return True if the request was handled or false if not handler handled it.
   */
  boolean handleChain(ContainerCheckRequest request);

  /**
   * Add a subsequent HealthCheck that will be tried only if the current check
   * returns false. This allows handlers to be chained together, and each will
   * be tried in turn until one succeeds.
   * @param handler
   * @return
   */
  HealthCheck addNext(HealthCheck handler);

}