How to prevent websockify process spawned by Django process getting killed when restarting Django server?

Question

Please note, the Django server is Daphne, but the websockify command has nothing to do with Daphne channels.

I have the following oversimplified code in Django view:

def openvnc_connection(request):
    Popen(['websockify'. "--run-once", "--daemon", "--timeout", "30", "--idle-timeout", "60", "--cert", ...])
    ...

Problem is when I deploy the code, involves restarting the Daphne worker service, the websockify process gets killed as well, resulting any active vnc connection gets dropped.

I am aware the websockify process is the child of the django process and it gets killed because of that.

I have tried the double-fork or similar stuff like detaching the child process but they don't seem to work and websockify process still gets killed when restarting Daphne worker.

Tried double fork:

def spawnDaemon(port, target):
    import os, sys, subprocess
    # do the UNIX double-fork magic, see Stevens' "Advanced
    # Programming in the UNIX Environment" for details (ISBN 0201563177)
    try:
        pid = os.fork()
        if pid > 0:
            # parent process, return and keep running
            return
    except Exception as e:
        print(sys.stderr, "fork #1 failed: %d (%s)" % (e.errno, e.strerror))
        sys.exit(1)

    os.setsid()

    # do second fork
    try:
        pid = os.fork()
        if pid > 0:
            # exit from second parent
            sys.exit(0)
    except Exception as e:
        print(sys.stderr, "fork #2 failed: %d (%s)" % (e.errno, e.strerror))
        sys.exit(1)

    # do stuff
    Popen(['websockify'. "--run-once", "--daemon", "--timeout", "30", "--idle-timeout", "60", "--cert", ...])

    # all done
    os._exit(os.EX_OK)

score 0 · Accepted Answer · answered Aug 28 '20 at 03:15

So... I went for a huge detour, tried to spawn the websockify through another python code which does the double fork:

def double_fork():
    try:
        pid = os.fork()
        if pid > 0:
            # parent process, return and keep running
            return
    except Exception as e:
        sys.exit(1)

    os.setsid()

    # do second fork
    try:
        pid = os.fork()
        if pid > 0:
            # exit from second parent
            sys.exit(0)
    except Exception as e:
        logger.error("fork #2 failed: %d (%s)" % (e.errno, e.strerror))
        sys.exit(1)

    from websockify.websocketproxy import WebSocketProxy, LibProxyServer
    WebSocketProxy(run_once=True, timeout=30, idle_timeout=60, target_host=sys.argv[1], target_port=sys.argv[2], listen_port=sys.argv[3],
            cert=cert, key=key, daemon=False).start_server()

Which led to able to double forked fine but still getting killed when I run sudo systemctl restart ..., then further searching found this answer, and it worked for me, just need to add to the service block.

KillMode=process

Then I also tried without the new python script to double fork, by just calling the old Popen(...), I believe it also spawns a daemon process, and it's also working.

How to prevent websockify process spawned by Django process getting killed when restarting Django server?

1 Answers1