| /** |
| * 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.http; |
| |
| import javax.servlet.http.HttpServlet; |
| import javax.servlet.http.HttpServletRequest; |
| import javax.servlet.http.HttpServletResponse; |
| import java.io.IOException; |
| |
| /** |
| * Used by Load Balancers to detect the active NameNode/ResourceManager/Router. |
| */ |
| public abstract class IsActiveServlet extends HttpServlet { |
| |
| /** Default serial identifier. */ |
| private static final long serialVersionUID = 1L; |
| |
| public static final String SERVLET_NAME = "isActive"; |
| public static final String PATH_SPEC = "/isActive"; |
| |
| public static final String RESPONSE_ACTIVE = |
| "I am Active!"; |
| |
| public static final String RESPONSE_NOT_ACTIVE = |
| "I am not Active!"; |
| |
| /** |
| * Check whether this instance is the Active one. |
| * @param req HTTP request |
| * @param resp HTTP response to write to |
| */ |
| @Override |
| public void doGet( |
| final HttpServletRequest req, final HttpServletResponse resp) |
| throws IOException { |
| |
| // By default requests are persistent. We don't want long-lived connections |
| // on server side. |
| resp.addHeader("Connection", "close"); |
| |
| if (!isActive()) { |
| // Report not SC_OK |
| resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, |
| RESPONSE_NOT_ACTIVE); |
| return; |
| } |
| resp.setStatus(HttpServletResponse.SC_OK); |
| resp.getWriter().write(RESPONSE_ACTIVE); |
| resp.getWriter().flush(); |
| } |
| |
| /** |
| * @return true if this instance is in Active HA state. |
| */ |
| protected abstract boolean isActive(); |
| } |