org.apache.hadoop.ha.ShellCommandFencer 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 java.io.IOException;
import java.lang.reflect.Field;
import java.util.Map;
import org.apache.hadoop.conf.Configured;
import com.google.common.annotations.VisibleForTesting;
import org.apache.hadoop.util.Shell;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Fencing method that runs a shell command. It should be specified
* in the fencing configuration like:
*
* shell(/path/to/my/script.sh arg1 arg2 ...)
*
* The string between '(' and ')' is passed directly to a bash shell
* (cmd.exe on Windows) and may not include any closing parentheses.
*
* The shell command will be run with an environment set up to contain
* all of the current Hadoop configuration variables, with the '_' character
* replacing any '.' characters in the configuration keys.
*
* If the shell command returns an exit code of 0, the fencing is
* determined to be successful. If it returns any other exit code, the
* fencing was not successful and the next fencing method in the list
* will be attempted.
*
* Note: this fencing method does not implement any timeout.
* If timeouts are necessary, they should be implemented in the shell
* script itself (eg by forking a subshell to kill its parent in
* some number of seconds).
*/
public class ShellCommandFencer
extends Configured implements FenceMethod {
/** Length at which to abbreviate command in long messages */
private static final int ABBREV_LENGTH = 20;
/** Prefix for target parameters added to the environment */
private static final String TARGET_PREFIX = "target_";
@VisibleForTesting
static Logger LOG = LoggerFactory.getLogger(ShellCommandFencer.class);
@Override
public void checkArgs(String args) throws BadFencingConfigurationException {
if (args == null || args.isEmpty()) {
throw new BadFencingConfigurationException(
"No argument passed to 'shell' fencing method");
}
// Nothing else we can really check without actually running the command
}
@Override
public boolean tryFence(HAServiceTarget target, String cmd) {
ProcessBuilder builder;
if (!Shell.WINDOWS) {
builder = new ProcessBuilder("bash", "-e", "-c", cmd);
} else {
builder = new ProcessBuilder("cmd.exe", "/c", cmd);
}
setConfAsEnvVars(builder.environment());
addTargetInfoAsEnvVars(target, builder.environment());
Process p;
try {
p = builder.start();
p.getOutputStream().close();
} catch (IOException e) {
LOG.warn("Unable to execute " + cmd, e);
return false;
}
String pid = tryGetPid(p);
LOG.info("Launched fencing command '" + cmd + "' with "
+ ((pid != null) ? ("pid " + pid) : "unknown pid"));
String logPrefix = abbreviate(cmd, ABBREV_LENGTH);
if (pid != null) {
logPrefix = "[PID " + pid + "] " + logPrefix;
}
// Pump logs to stderr
StreamPumper errPumper = new StreamPumper(
LOG, logPrefix, p.getErrorStream(),
StreamPumper.StreamType.STDERR);
errPumper.start();
StreamPumper outPumper = new StreamPumper(
LOG, logPrefix, p.getInputStream(),
StreamPumper.StreamType.STDOUT);
outPumper.start();
int rc;
try {
rc = p.waitFor();
errPumper.join();
outPumper.join();
} catch (InterruptedException ie) {
LOG.warn("Interrupted while waiting for fencing command: " + cmd);
return false;
}
return rc == 0;
}
/**
* Abbreviate a string by putting '...' in the middle of it,
* in an attempt to keep logs from getting too messy.
* @param cmd the string to abbreviate
* @param len maximum length to abbreviate to
* @return abbreviated string
*/
static String abbreviate(String cmd, int len) {
if (cmd.length() > len && len >= 5) {
int firstHalf = (len - 3) / 2;
int rem = len - firstHalf - 3;
return cmd.substring(0, firstHalf) +
"..." + cmd.substring(cmd.length() - rem);
} else {
return cmd;
}
}
/**
* Attempt to use evil reflection tricks to determine the
* pid of a launched process. This is helpful to ops
* if debugging a fencing process that might have gone
* wrong. If running on a system or JVM where this doesn't
* work, it will simply return null.
*/
private static String tryGetPid(Process p) {
try {
Class clazz = p.getClass();
if (clazz.getName().equals("java.lang.UNIXProcess")) {
Field f = clazz.getDeclaredField("pid");
f.setAccessible(true);
return String.valueOf(f.getInt(p));
} else {
LOG.trace("Unable to determine pid for " + p
+ " since it is not a UNIXProcess");
return null;
}
} catch (Throwable t) {
LOG.trace("Unable to determine pid for " + p, t);
return null;
}
}
/**
* Set the environment of the subprocess to be the Configuration,
* with '.'s replaced by '_'s.
*/
private void setConfAsEnvVars(Map env) {
for (Map.Entry pair : getConf()) {
env.put(pair.getKey().replace('.', '_'), pair.getValue());
}
}
/**
* Add information about the target to the the environment of the
* subprocess.
*
* @param target
* @param environment
*/
private void addTargetInfoAsEnvVars(HAServiceTarget target,
Map environment) {
for (Map.Entry e :
target.getFencingParameters().entrySet()) {
String key = TARGET_PREFIX + e.getKey();
key = key.replace('.', '_');
environment.put(key, e.getValue());
}
}
}