001/** 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, software 013 * distributed under the License is distributed on an "AS IS" BASIS, 014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 015 * See the License for the specific language governing permissions and 016 * limitations under the License. 017 */ 018package org.apache.hadoop.ha; 019 020import org.apache.hadoop.classification.InterfaceAudience; 021import org.apache.hadoop.classification.InterfaceStability; 022import org.apache.hadoop.conf.Configurable; 023 024/** 025 * A fencing method is a method by which one node can forcibly prevent 026 * another node from making continued progress. This might be implemented 027 * by killing a process on the other node, by denying the other node's 028 * access to shared storage, or by accessing a PDU to cut the other node's 029 * power. 030 * <p> 031 * Since these methods are often vendor- or device-specific, operators 032 * may implement this interface in order to achieve fencing. 033 * <p> 034 * Fencing is configured by the operator as an ordered list of methods to 035 * attempt. Each method will be tried in turn, and the next in the list 036 * will only be attempted if the previous one fails. See {@link NodeFencer} 037 * for more information. 038 * <p> 039 * If an implementation also implements {@link Configurable} then its 040 * <code>setConf</code> method will be called upon instantiation. 041 */ 042@InterfaceAudience.Public 043@InterfaceStability.Unstable 044public interface FenceMethod { 045 /** 046 * Verify that the given fencing method's arguments are valid. 047 * @param args the arguments provided in the configuration. This may 048 * be null if the operator did not configure any arguments. 049 * @throws BadFencingConfigurationException if the arguments are invalid 050 */ 051 public void checkArgs(String args) throws BadFencingConfigurationException; 052 053 /** 054 * Attempt to fence the target node. 055 * @param serviceAddr the address (host:ipcport) of the service to fence 056 * @param args the configured arguments, which were checked at startup by 057 * {@link #checkArgs(String)} 058 * @return true if fencing was successful, false if unsuccessful or 059 * indeterminate 060 * @throws BadFencingConfigurationException if the configuration was 061 * determined to be invalid only at runtime 062 */ 063 public boolean tryFence(HAServiceTarget target, String args) 064 throws BadFencingConfigurationException; 065}