/**
* 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 com.alibaba.wasp;
import com.alibaba.wasp.zookeeper.MasterAddressTracker;
import com.alibaba.wasp.zookeeper.ZooKeeperWatcher;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.Abortable;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
/**
* <p>
* Contains a set of methods for the collaboration between the start/stop
* scripts and the servers. It allows to delete immediately the znode when the
* master or the entityGroups server crashes. The entityGroup server / master
* writes a specific file when it starts / becomes main master. When they end
* properly, they delete the file.
* </p>
* <p>
* In the script, we check for the existence of these files when the program
* ends. If they still exist we conclude that the server crashed, likely without
* deleting their znode. To have a faster recovery we delete immediately the
* znode.
* </p>
* <p>
* The strategy depends on the server type. For a entityGroup server we store
* the znode path in the file, and use it to delete it. for a master, as the
* znode path constant whatever the server, we check its content to make sure
* that the backup server is not now in charge.
* </p>
*/
public class ZNodeClearer {
public static final Log LOG = LogFactory.getLog(ZNodeClearer.class);
private ZNodeClearer() {
}
/**
* Logs the errors without failing on exception.
*/
public static void writeMyEphemeralNodeOnDisk(String fileContent) {
String fileName = ZNodeClearer.getMyEphemeralNodeFileName();
if (fileName == null) {
LOG.warn("No filename given to save the znode used, it won't be saved "
+ "(Environment variable WASP_ZNODE_FILE is not set).");
return;
}
FileWriter fstream;
try {
fstream = new FileWriter(fileName);
} catch (IOException e) {
LOG.warn("Can't write znode file " + fileName, e);
return;
}
BufferedWriter out = new BufferedWriter(fstream);
try {
try {
out.write(fileContent + "\n");
} finally {
try {
out.close();
} finally {
fstream.close();
}
}
} catch (IOException e) {
LOG.warn("Can't write znode file " + fileName, e);
}
}
/**
* read the content of znode file, expects a single line.
*/
public static String readMyEphemeralNodeOnDisk() throws IOException {
String fileName = getMyEphemeralNodeFileName();
if (fileName == null) {
throw new IOException("No filename");
}
FileReader znodeFile = new FileReader(fileName);
BufferedReader br = new BufferedReader(znodeFile);
String file_content = br.readLine();
br.close();
return file_content;
}
/**
* Get the name of the file used to store the znode contents
*/
public static String getMyEphemeralNodeFileName() {
return System.getenv().get("WASP_ZNODE_FILE");
}
/**
* delete the znode file
*/
public static void deleteMyEphemeralNodeOnDisk() {
String fileName = getMyEphemeralNodeFileName();
if (fileName != null) {
new File(fileName).delete();
}
}
/**
* Delete the master znode if its content (ServerName string) is the same as
* the one in the znode file. (env: HBASE_ZNODE_FILE).
*
* @return true on successful deletion, false otherwise.
*/
public static boolean clear(Configuration conf) {
Configuration tempConf = new Configuration(conf);
tempConf.setInt("zookeeper.recovery.retry", 0);
ZooKeeperWatcher zkw;
try {
zkw = new ZooKeeperWatcher(tempConf, "clean znode for master",
new Abortable() {
@Override
public void abort(String why, Throwable e) {
}
@Override
public boolean isAborted() {
return false;
}
});
} catch (IOException e) {
LOG.warn("Can't connect to zookeeper to read the master znode", e);
return false;
}
String znodeFileContent;
try {
znodeFileContent = ZNodeClearer.readMyEphemeralNodeOnDisk();
} catch (IOException e) {
LOG.warn("Can't read the content of the znode file", e);
return false;
}
return MasterAddressTracker.deleteIfEquals(zkw, znodeFileContent);
}
}