| /* |
| * 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.sling.discovery; |
| |
| import java.util.List; |
| |
| import org.osgi.annotation.versioning.ProviderType; |
| |
| |
| /** |
| * A ClusterView represents the instances of a cluster that are |
| * up and running and that all can see each other at a certain point in time. |
| * <p> |
| * 'Seeing each other'/A cluster refers to being hooked to the same underlying |
| * persistence layer/jcr repository. |
| * <p> |
| * A ClusterView can also consist of just one single instance. |
| * <p> |
| * All instances in a cluster must and do have a unique sling.id. |
| * @see InstanceDescription#getSlingId() |
| */ |
| @ProviderType |
| public interface ClusterView { |
| |
| /** |
| * Returns a stable id of the cluster represented by this |
| * cluster view. |
| * <p> |
| * Similar to the SlingID, this id is persisted and thus |
| * remains stable accross instance/cluster restarts. |
| * <p> |
| * When an instance joins a cluster, it will inherit |
| * the id from the joined cluster (thus incurs a cluster id |
| * change). |
| * <p> |
| * Note: When instances part from a cluster (eg due to a network |
| * partitioning) the cluster id is retained. This results in |
| * potentially multiple clusters with the same id. This |
| * fact could be used to detect such partitioning/split brain |
| * situations. It also implies though that the cluster id |
| * is not guaranteed to be unique in a topology! |
| * <p> |
| * Addition in 1.0.4: this id must consist only of alphanumeric |
| * characters plus dash '-' and underscore '_'. |
| * @return an id of this cluster view |
| * @see <a href="http://issues.apache.org/jira/browse/SLING-3164">SLING-3164</a> |
| * @since exists since 1.0.0 - stable since 1.0.2 - alphanumeric + '_' and'-' since 1.0.4 |
| */ |
| String getId(); |
| |
| /** |
| * Provides the list of InstanceDescriptions with a stable ordering. |
| * <p> |
| * Stable ordering implies that unless an instance leaves the cluster |
| * (due to shutdown/crash/network problems) the instance keeps the |
| * relative position in the list. |
| * @return the list of InstanceDescriptions (with a stable ordering) |
| */ |
| List<InstanceDescription> getInstances(); |
| |
| /** |
| * Provides the InstanceDescription belonging to the leader instance. |
| * <p> |
| * Every ClusterView is guaranteed to have one and only one leader. |
| * <p> |
| * The leader is stable: once a leader is elected it stays leader |
| * unless it leaves the cluster (due to shutdown/crash/network problems) |
| * @return the InstanceDescription belonging to the leader instance |
| */ |
| InstanceDescription getLeader(); |
| } |