001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.ha;
019
020import org.apache.hadoop.classification.InterfaceAudience;
021import org.apache.hadoop.classification.InterfaceStability;
022import org.apache.hadoop.fs.CommonConfigurationKeys;
023import org.apache.hadoop.io.retry.Idempotent;
024import org.apache.hadoop.security.AccessControlException;
025import org.apache.hadoop.security.KerberosInfo;
026
027import java.io.IOException;
028
029/**
030 * Protocol interface that provides High Availability related primitives to
031 * monitor and fail-over the service.
032 * 
033 * This interface could be used by HA frameworks to manage the service.
034 */
035@KerberosInfo(
036    serverPrincipal=CommonConfigurationKeys.HADOOP_SECURITY_SERVICE_USER_NAME_KEY)
037@InterfaceAudience.Public
038@InterfaceStability.Evolving
039public interface HAServiceProtocol {
040  /**
041   * Initial version of the protocol
042   */
043  public static final long versionID = 1L;
044
045  /**
046   * An HA service may be in active or standby state. During startup, it is in
047   * an unknown INITIALIZING state. During shutdown, it is in the STOPPING state
048   * and can no longer return to active/standby states.
049   */
050  public enum HAServiceState {
051    INITIALIZING("initializing"),
052    ACTIVE("active"),
053    STANDBY("standby"),
054    STOPPING("stopping");
055
056    private String name;
057
058    HAServiceState(String name) {
059      this.name = name;
060    }
061
062    @Override
063    public String toString() {
064      return name;
065    }
066  }
067  
068  public static enum RequestSource {
069    REQUEST_BY_USER,
070    REQUEST_BY_USER_FORCED,
071    REQUEST_BY_ZKFC;
072  }
073  
074  /**
075   * Information describing the source for a request to change state.
076   * This is used to differentiate requests from automatic vs CLI
077   * failover controllers, and in the future may include epoch
078   * information.
079   */
080  public static class StateChangeRequestInfo {
081    private final RequestSource source;
082
083    public StateChangeRequestInfo(RequestSource source) {
084      super();
085      this.source = source;
086    }
087
088    public RequestSource getSource() {
089      return source;
090    }
091  }
092
093  /**
094   * Monitor the health of service. This periodically called by the HA
095   * frameworks to monitor the health of the service.
096   * 
097   * Service is expected to perform checks to ensure it is functional.
098   * If the service is not healthy due to failure or partial failure,
099   * it is expected to throw {@link HealthCheckFailedException}.
100   * The definition of service not healthy is left to the service.
101   * 
102   * Note that when health check of an Active service fails,
103   * failover to standby may be done.
104   * 
105   * @throws HealthCheckFailedException
106   *           if the health check of a service fails.
107   * @throws AccessControlException
108   *           if access is denied.
109   * @throws IOException
110   *           if other errors happen
111   */
112  @Idempotent
113  public void monitorHealth() throws HealthCheckFailedException,
114                                     AccessControlException,
115                                     IOException;
116
117  /**
118   * Request service to transition to active state. No operation, if the
119   * service is already in active state.
120   * 
121   * @throws ServiceFailedException
122   *           if transition from standby to active fails.
123   * @throws AccessControlException
124   *           if access is denied.
125   * @throws IOException
126   *           if other errors happen
127   */
128  @Idempotent
129  public void transitionToActive(StateChangeRequestInfo reqInfo)
130                                   throws ServiceFailedException,
131                                          AccessControlException,
132                                          IOException;
133
134  /**
135   * Request service to transition to standby state. No operation, if the
136   * service is already in standby state.
137   * 
138   * @throws ServiceFailedException
139   *           if transition from active to standby fails.
140   * @throws AccessControlException
141   *           if access is denied.
142   * @throws IOException
143   *           if other errors happen
144   */
145  @Idempotent
146  public void transitionToStandby(StateChangeRequestInfo reqInfo)
147                                    throws ServiceFailedException,
148                                           AccessControlException,
149                                           IOException;
150
151  /**
152   * Return the current status of the service. The status indicates
153   * the current <em>state</em> (e.g ACTIVE/STANDBY) as well as
154   * some additional information.
155   * 
156   * @throws AccessControlException
157   *           if access is denied.
158   * @throws IOException
159   *           if other errors happen
160   * @see HAServiceStatus
161   */
162  @Idempotent
163  public HAServiceStatus getServiceStatus() throws AccessControlException,
164                                                   IOException;
165}