zk-flock

You can use zk-flock to run programs in a cluster under a distributed lock to limit overall amount of instances.

Configuration

You have to write the configuration file /etc/distributed-flock.json with the following content:

{
    "host": ["hostname1:2181","hostname2:2181","hostname3:2181"],
    "timeout": 5,
    "app_id": "my_application_namespace",
    "sleep": "ON",    //ON or OFF - Default OFF
    "maxla": 30,      // If >=0 -> max loadaverage for work. Default -1
    "logger": {
            "path": "/tmp/zkflock.log",
            "level": "INFO",
            "zklevel": "ERROR"
    },
    "auth": {
        "scheme": "digest",
        "data": "noxiouz:password"
    }
}

• host - list of Zookeeper nodes
• timeout - timeout for zookeper connection (sec)
• app_id - namespace for your application in Zookeeper. This means that the lock will be stored in Zookeeper with path likes /app_id/your_lock_name
• sleep - Sleep before work. Default: "OFF". Switch "ON" by -s (--sleep).
• maxla - Maximal load average. Use if >=0. Default: -1. Set by -m (--maxla).

Logging

• path - path to log file (default: /dev/null)
• level - logging level of zk-flock (default: INFO)
• zklevel - logging level of Zookeeper Client (default: WARN)

Both loglevels are one of values: ERROR, WARN, INFO, DEBUG

Usage

To run the application under the supervision of the zk-flock use the command:

zk-flock <pidname> <application command>

If your application requires command-line arguments enclose it in double quotes:

zk-flock my_test_lock "bash /home/user/test.sh arg1 arg2 arg3"

For attempting to lock lasted for a specific time, use the -w option (--wait) setting the time in seconds. Add key -d or --daemonize to starts this appliction as daemon.

If need set minimum time in seconds for lock use the -l option (--minlocktime) - default 5 sec

Use -p or --pdeathsig to specify a signal that will be sent if the master process died. By default the signal is SIGTERM.

Non Linux usage warning

If you kill zk-flock application with kill -9, the lock will be released, but this will not stop your application.