content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.master.service;
  
  /**
   * Defines a simple start/promote/demote/stop interface for interacting with simple Alluxio
   * master components such as the web server, metrics server, rpc server, etc...
   */
  public interface SimpleService {
    /**
     * Starts the service. Leaves the service in {@link alluxio.grpc.NodeState#STANDBY} state.
     * Leaves the service in the same state as {@link #demote()}.
     * Can only be called once.
     */
    void start();
  
    /**
     * Promotes the service to {@link alluxio.grpc.NodeState#PRIMARY} state.
     * Can only be called on a started service (i.e. {@link #start()} must precede this method).
     * Can only be called in {@link alluxio.grpc.NodeState#STANDBY} state.
     * Can be called multiple times (e.g. a service is promoted, then demoted, then promoted again).
     */
    void promote();
  
    /**
     * Demotes the service back to {@link alluxio.grpc.NodeState#STANDBY} state.
     * Can only be called on a started service (i.e. {@link #start()} must precede this method).
     * Can only be called in {@link alluxio.grpc.NodeState#PRIMARY} state (i.e. {@link #promote()}
     * must precede this method).
     * Can be called multiple times (e.g. a service is promoted, then demoted, then promoted again,
     * and demoted again).
     */
    void demote();
  
    /**
     * Stops the service altogether and cleans up any state left.
     * If {@link #start()} has not been called on this service this method should be a noop.
     * Can only be called once.
     */
    void stop();
  }
  