org.apache.hadoop.ha.FenceMethod Maven / Gradle / Ivy
/**
* 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.conf.Configurable;
/**
* A fencing method is a method by which one node can forcibly prevent
* another node from making continued progress. This might be implemented
* by killing a process on the other node, by denying the other node's
* access to shared storage, or by accessing a PDU to cut the other node's
* power.
*
* Since these methods are often vendor- or device-specific, operators
* may implement this interface in order to achieve fencing.
*
* Fencing is configured by the operator as an ordered list of methods to
* attempt. Each method will be tried in turn, and the next in the list
* will only be attempted if the previous one fails. See {@link NodeFencer}
* for more information.
*
* If an implementation also implements {@link Configurable} then its
* setConf method will be called upon instantiation.
*/
@InterfaceAudience.Public
@InterfaceStability.Unstable
public interface FenceMethod {
/**
* Verify that the given fencing method's arguments are valid.
* @param args the arguments provided in the configuration. This may
* be null if the operator did not configure any arguments.
* @throws BadFencingConfigurationException if the arguments are invalid
*/
public void checkArgs(String args) throws BadFencingConfigurationException;
/**
* Attempt to fence the target node.
* @param target the target of the service to fence
* @param args the configured arguments, which were checked at startup by
* {@link #checkArgs(String)}
* @return true if fencing was successful, false if unsuccessful or
* indeterminate
* @throws BadFencingConfigurationException if the configuration was
* determined to be invalid only at runtime
*/
public boolean tryFence(HAServiceTarget target, String args)
throws BadFencingConfigurationException;
}