| /** |
| * 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. |
| * <p> |
| * Since these methods are often vendor- or device-specific, operators |
| * may implement this interface in order to achieve fencing. |
| * <p> |
| * 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. |
| * <p> |
| * If an implementation also implements {@link Configurable} then its |
| * <code>setConf</code> 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 address (host:ipcport) 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; |
| } |