How do I terminate a flask app that's running as a service?

Question

I was able to get my flask app running as a service thanks to Is it possible to run a Python script as a service in Windows? If possible, how?, but when it comes to stopping it i cannot. I have to terminate the process in task manager.

Here's my run.py which I turn into a service via run.py install:

from app import app

from multiprocessing import Process
import win32serviceutil
import win32service
import win32event
import servicemanager
import socket


class AppServerSvc (win32serviceutil.ServiceFramework):
    _svc_name_ = "CCApp"
    _svc_display_name_ = "CC App"

    def __init__(self,args):
        win32serviceutil.ServiceFramework.__init__(self,args)
        self.hWaitStop = win32event.CreateEvent(None,0,0,None)
        socket.setdefaulttimeout(60)

    def SvcStop(self):
        self.ReportServiceStatus(win32service.SERVICE_STOP_PENDING)
        win32event.SetEvent(self.hWaitStop)
        server.terminate()
        server.join()

    def SvcDoRun(self):
        servicemanager.LogMsg(servicemanager.EVENTLOG_INFORMATION_TYPE,
                              servicemanager.PYS_SERVICE_STARTED,
                              (self._svc_name_,''))
        self.main()

    def main(self):
        server = Process(app.run(host = '192.168.1.6'))
        server.start()

if __name__ == '__main__':
    win32serviceutil.HandleCommandLine(AppServerSvc)

I got the process stuff from this post: http://librelist.com/browser/flask/2011/1/10/start-stop-flask/#a235e60dcaebaa1e134271e029f801fe but unfortunately it doesn't work either.

The log file in Event Viewer says that the global variable 'server' is not defined. However, i've made server a global variable and it still gives me the same error.

Okay, a couple of things wrong with this. 1. `server` is not defined in `SvcStop`, that's why you get that error message. 2. `server = Process(app.run(host = '192.168.1.6'))` does not do what you think it does. Why do you think you need to run the app in a separate process anyway? — univerio, May 09 '14 at 00:20
How did you set server as a global variable? Local variables shadow global ones in Python automatically, so you may need to [use the `global` statement](http://stackoverflow.com/questions/4693120/) to assign to global variables in local scope. — uranusjr, May 09 '14 at 00:23
@univerio I only added that server and process code because I was looking for a way to terminate the server in SvcStop. There is app.run() for flask, but there is no app.stop() or its equivalent. — Chockomonkey, May 09 '14 at 18:18
@uranusjr I did try this, by doing: `global server server = Process(app.run(host= '192.168.1.6'))` — Chockomonkey, May 09 '14 at 18:19
Flask listens for SIGINT to see if it should exit. Perhaps you could send a signal to yourself in `SvcStop`? Alternatively, if you really really wanted to run the app in a separate process, make sure you set the `target` keyword arg to `app.run` instead of calling `app.run` directly. — univerio, May 09 '14 at 18:28
@univerio Nope, I don't care about it running in a process at all--I just want to be able to terminate my app from running. If I can do this with SIGINT, great! Problem is, I can't find any documentation on how to issue a kill command with this... — Chockomonkey, May 09 '14 at 22:30
Look into [`os.kill`](https://docs.python.org/2/library/os.html#os.kill). On Windows, you'll probably want to send the [`signal.CTRL_C_EVENT`](https://docs.python.org/2/library/signal.html#signal.CTRL_C_EVENT) signal instead. I have no clue if that works, but try it. Side note: `app.run` starts a development server; for production, you probably want to use a real server like Apache or IIS. — univerio, May 09 '14 at 22:55

score 16 · Answer 1 · answered May 09 '14 at 23:44

16

You can stop the Werkzeug web server gracefully before you stop the Win32 server. Example:

from flask import request

def shutdown_server():
    func = request.environ.get('werkzeug.server.shutdown')
    if func is None:
        raise RuntimeError('Not running with the Werkzeug Server')
    func()

@app.route('/shutdown', methods=['POST'])
def shutdown():
    shutdown_server()
    return 'Server shutting down...'

If you add this to your Flask server you can then request a graceful server shutdown by sending a POST request to /shutdown. You can use requests or urllib2 to do this. Depending on your situation you may need to protect this route against unauthorized access.

Once the server has stopped I think you will have to no problem stopping the Win32 service.

Note that the shutdown code above appears in this Flask snippet.

answered May 09 '14 at 23:44

Miguel Grinberg

65,299
14
133
152

Thanks for the response. I began implementing this but in talking with a friend got convinced that tricking the development server to run as a service was not the best of ideas I've had. Anyway, as posted below i ended up setting up a real server to host my web app! Also, just have to say that your blog is what got me into coding Flask. So, cheers Miguel! – Chockomonkey May 28 '14 at 23:14
Is there a way to get a zero return value? – GuySoft Mar 21 '18 at 14:56
1

This has since been deprecated https://github.com/microsoft/debugpy/issues/628#issuecomment-848237040 – Rick Nov 22 '22 at 03:21

JohnTheWalker · Answer 2 · 2019-05-16T15:23:23.050

You could also trick Flask into believing you pressed Ctrl + C:

def shutdown_flask(self):
    from win32api import GenerateConsoleCtrlEvent
    CTRL_C_EVENT = 0
    GenerateConsoleCtrlEvent(CTRL_C_EVENT, 0)

Then simply call shutdown_flask() in your SvcStop():

try:
    # try to exit gracefully
    self.shutdown_flask()
except Exception as e:
    # force quit
    os._exit(0)

Should shutdown_flask() fail for some reason, os._exit() makes sure your service will end (albeit with a nasty warning), by halting the interpreter.

score 2 · Accepted Answer · edited May 23 '17 at 10:33

2

I recommend you use http://supervisord.org/. Actually not work in Windows, but with Cygwin you can run supervisor as in Linux, including run as service.

For install Supervisord: https://stackoverflow.com/a/18032347/3380763

After install you must configure the app, here an example: http://flaviusim.com/blog/Deploying-Flask-with-nginx-uWSGI-and-Supervisor/ (Is not necessary that you use Nginx with the Supervisor's configuration is enough)

edited May 23 '17 at 10:33

Community

1
1

answered May 11 '14 at 04:32

yograterol

593
3
7

Thank you. I didn't go the route you suggested, but I ended up with a Ubuntu server with nginx and uwsgi. – Chockomonkey May 28 '14 at 23:14

How do I terminate a flask app that's running as a service?

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