server-api/src/main/java/org/apache/atlas/listener/ActiveStateChangeHandler.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.atlas.listener;

import org.apache.atlas.AtlasException;

/**
 * An interface that should be implemented by objects and services to react to changes in state of an Atlas server.
 *
 * The two state transitions we handle are (1) becoming active and (2) becoming passive.
 */
public interface ActiveStateChangeHandler {
    public enum HandlerOrder {
        AUDIT_REPOSITORY(0),
        GRAPH_BACKED_SEARCH_INDEXER(1),
        TYPEDEF_STORE_INITIALIZER(2),
        ATLAS_PATCH_SERVICE(3),
        DEFAULT_METADATA_SERVICE(4),
        NOTIFICATION_HOOK_CONSUMER(5),
        TASK_MANAGEMENT(6);

        private final int order;

        private HandlerOrder(int order) {
            this.order = order;
        }

        public int getOrder() { return order; }
    }

    /**
     * Callback that is invoked on an implementor when this instance of Atlas server is declared the leader.
     *
     * Any initialization that must be carried out by an implementor only when the server becomes active
     * should happen on this callback.
     *
     * @throws {@link AtlasException} if anything is wrong on initialization
     */
    void instanceIsActive() throws AtlasException;

    /**
     * Callback that is invoked on an implementor when this instance of Atlas server is removed as the leader.
     *
     * Any cleanup that must be carried out by an implementor when the server becomes passive
     * should happen on this callback.
     *
     * @throws {@link AtlasException} if anything is wrong on shutdown
     */
    void instanceIsPassive() throws AtlasException;


    /**
     * Defines the order in which the handler should be called.
     *   When state becomes active, the handler will be called from low order to high
     *   When state becomes passive, the handler will be called from high order to low
     *
     */
    int getHandlerOrder();
}