modules/core/src/main/java/org/apache/ignite/plugin/segmentation/SegmentationResolver.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.ignite.plugin.segmentation;

import java.io.Serializable;
import org.apache.ignite.IgniteCheckedException;
import org.apache.ignite.configuration.IgniteConfiguration;

/**
 * This is interface for segmentation (a.k.a "split-brain" problem) resolvers.
 * <p>
 * Each segmentation resolver checks segment for validity, using its inner logic.
 * Typically, resolver should run light-weight single check (i.e. one IP address or
 * one shared folder). Compound segment checks may be performed using several
 * resolvers.
 * <p>
 * Note that Ignite support a logical segmentation and not limited to network
 * related segmentation only. For example, a particular segmentation resolver
 * can check for specific application or service present on the network and
 * mark the topology as segmented in case it is not available. In other words
 * you can equate the service outage with network outage via segmentation resolution
 * and employ the unified approach in dealing with these types of problems.
 * @see IgniteConfiguration#getSegmentationResolvers()
 * @see IgniteConfiguration#getSegmentationPolicy()
 * @see IgniteConfiguration#getSegmentCheckFrequency()
 * @see IgniteConfiguration#isAllSegmentationResolversPassRequired()
 * @see IgniteConfiguration#isWaitForSegmentOnStart()
 * @see SegmentationPolicy
 */
public interface SegmentationResolver extends Serializable {
    /**
     * Checks whether segment is valid.
     * <p>
     * When segmentation happens every node ends up in either one of two segments:
     * <ul>
     *     <li>Correct segment</li>
     *     <li>Invalid segment</li>
     * </ul>
     * Nodes in correct segment will continue operate as if nodes in the invalid segment
     * simply left the topology (i.e. the topology just got "smaller"). Nodes in the
     * invalid segment will realized that were "left out or disconnected" from the correct segment
     * and will try to reconnect via {@link SegmentationPolicy segmentation policy} set
     * in configuration.
     *
     * @return {@code True} if segment is correct, {@code false} otherwise.
     * @throws IgniteCheckedException If an error occurred.
     */
    public abstract boolean isValidSegment() throws IgniteCheckedException;
}