org.apache.hadoop.ha.HAServiceProtocol.java Source code

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Here is the source code for org.apache.hadoop.ha.HAServiceProtocol.java

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/**
 * 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.ha;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.fs.CommonConfigurationKeys;
import org.apache.hadoop.io.retry.Idempotent;
import org.apache.hadoop.security.AccessControlException;
import org.apache.hadoop.security.KerberosInfo;

import java.io.IOException;

/**
 * Protocol interface that provides High Availability related primitives to
 * monitor and fail-over the service.
 * 
 * This interface could be used by HA frameworks to manage the service.
 */
@KerberosInfo(serverPrincipal = CommonConfigurationKeys.HADOOP_SECURITY_SERVICE_USER_NAME_KEY)
@InterfaceAudience.Public
@InterfaceStability.Evolving
public interface HAServiceProtocol {
    /**
     * Initial version of the protocol
     */
    public static final long versionID = 1L;

    /**
     * An HA service may be in active or standby state. During startup, it is in
     * an unknown INITIALIZING state. During shutdown, it is in the STOPPING state
     * and can no longer return to active/standby states.
     */
    public enum HAServiceState {
        INITIALIZING("initializing"), ACTIVE("active"), STANDBY("standby"), STOPPING("stopping");

        private String name;

        HAServiceState(String name) {
            this.name = name;
        }

        @Override
        public String toString() {
            return name;
        }
    }

    public enum RequestSource {
        REQUEST_BY_USER, REQUEST_BY_USER_FORCED, REQUEST_BY_ZKFC;
    }

    /**
     * Information describing the source for a request to change state.
     * This is used to differentiate requests from automatic vs CLI
     * failover controllers, and in the future may include epoch
     * information.
     */
    public static class StateChangeRequestInfo {
        private final RequestSource source;

        public StateChangeRequestInfo(RequestSource source) {
            super();
            this.source = source;
        }

        public RequestSource getSource() {
            return source;
        }
    }

    /**
     * Monitor the health of service. This periodically called by the HA
     * frameworks to monitor the health of the service.
     * 
     * Service is expected to perform checks to ensure it is functional.
     * If the service is not healthy due to failure or partial failure,
     * it is expected to throw {@link HealthCheckFailedException}.
     * The definition of service not healthy is left to the service.
     * 
     * Note that when health check of an Active service fails,
     * failover to standby may be done.
     * 
     * @throws HealthCheckFailedException
     *           if the health check of a service fails.
     * @throws AccessControlException
     *           if access is denied.
     * @throws IOException
     *           if other errors happen
     */
    @Idempotent
    public void monitorHealth() throws HealthCheckFailedException, AccessControlException, IOException;

    /**
     * Request service to transition to active state. No operation, if the
     * service is already in active state.
     * 
     * @throws ServiceFailedException
     *           if transition from standby to active fails.
     * @throws AccessControlException
     *           if access is denied.
     * @throws IOException
     *           if other errors happen
     */
    @Idempotent
    public void transitionToActive(StateChangeRequestInfo reqInfo)
            throws ServiceFailedException, AccessControlException, IOException;

    /**
     * Request service to transition to standby state. No operation, if the
     * service is already in standby state.
     * 
     * @throws ServiceFailedException
     *           if transition from active to standby fails.
     * @throws AccessControlException
     *           if access is denied.
     * @throws IOException
     *           if other errors happen
     */
    @Idempotent
    public void transitionToStandby(StateChangeRequestInfo reqInfo)
            throws ServiceFailedException, AccessControlException, IOException;

    /**
     * Return the current status of the service. The status indicates
     * the current <em>state</em> (e.g ACTIVE/STANDBY) as well as
     * some additional information.
     * 
     * @throws AccessControlException
     *           if access is denied.
     * @throws IOException
     *           if other errors happen
     * @see HAServiceStatus
     */
    @Idempotent
    public HAServiceStatus getServiceStatus() throws AccessControlException, IOException;
}