org.apache.sling.discovery.InstanceDescription Maven / Gradle / Ivy
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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.sling.discovery;
import java.util.Map;
import aQute.bnd.annotation.ProviderType;
/**
* An InstanceDescription represents and contains information about an
* instance that is part of a TopologyView.
*
* Note that all methods are idempotent - they always return the same values
* on subsequent calls. Rather, on any change new InstanceDescriptions are created.
*
*
* @see TopologyView
*/
@ProviderType
public interface InstanceDescription {
/**
* Property containing a name for the instance.
* The instance should provide this property.
*/
String PROPERTY_NAME = "org.apache.sling.instance.name";
/**
* Property containing a description for the instance.
* The instance should provide this property.
*/
String PROPERTY_DESCRIPTION = "org.apache.sling.instance.description";
/**
* Property containing endpoints to connect to the instance. The
* value is a comma separated list.
* The instance should provide this property.
*/
String PROPERTY_ENDPOINTS = "org.apache.sling.instance.endpoints";
/**
* Returns the ClusterView of which this instance is part of.
*
* Every instance is part of a ClusterView even if it is standalone.
* @return the ClusterView
*/
ClusterView getClusterView();
/**
* If an instance is part of a cluster, it can potentially be a leader of that cluster -
* this information is queried here.
*
* If an instance is not part of a cluster, this method returns true.
*
* Only one instance of a cluster is guaranteed to be the leader at any time.
* This guarantee is provided by this service.
* If the leader goes down, the service elects a new leader and announces it to
* TopologyEventListener listeners.
* @return true if this instance is the - only - leader in this cluster,
* false if it is one of the slaves, or true if it is not at all part of a cluster
*/
boolean isLeader();
/**
* Determines whether this InstanceDescription is representing the local instance.
* @return whether this InstanceDescription is representing the local instance.
*/
boolean isLocal();
/**
* The identifier of the running Sling instance.
*/
String getSlingId();
/**
* Returns the value of a particular property.
*
* Note that there are no hard guarantees or requirements as to how quickly
* a property is available once it is set on a distant instance.
* @param name The property name
* @return The value of the property or null
* @see DiscoveryService#setProperty(String, String)
*/
String getProperty(final String name);
/**
* Returns a Map containing all properties of this instance.
* This method always returns a map, it might be empty. The returned map
* is not modifiable.
* @return a Map containing all properties of this instance
*/
Map getProperties();
}