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.

Answer 1

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)

Answer 2

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.

Answer 3

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.