How to set up autoreload with Flask+uWSGI?

Question

I am looking for something like uWSGI + django autoreload mode for Flask.

Answer 1

The auto-reloading functionality of development-mode Flask is actually provided by the underlying Werkzeug library. The relevant code is in werkzeug/serving.py -- it's worth taking a look at. But basically, the main application spawns the WSGI server as a subprocess that stats every active .py file once per second, looking for changes. If it sees any, the subprocess exits, and the parent process starts it back up again -- in effect reloading the chages.

There's no reason you couldn't implement a similar technique at the layer of uWSGI. If you don't want to use a stat loop, you can try using underlying OS file-watch commands. Apparently (according to Werkzeug's code), pyinotify is buggy, but perhaps Watchdog works? Try a few things out and see what happens.

Edit:

In response to the comment, I think this would be pretty easy to reimplement. Building on the example provided from your link, along with the code from werkzeug/serving.py:

""" NOTE: _iter_module_files() and check_for_modifications() are both
    copied from Werkzeug code. Include appropriate attribution if
    actually used in a project. """
import uwsgi
from uwsgidecorators import timer

import sys
import os

def _iter_module_files():
    for module in sys.modules.values():
        filename = getattr(module, '__file__', None)
        if filename:
            old = None
            while not os.path.isfile(filename):
                old = filename
                filename = os.path.dirname(filename)
                if filename == old:
                    break
            else:
                if filename[-4:] in ('.pyc', '.pyo'):
                    filename = filename[:-1]
                yield filename

@timer(3)
def check_for_modifications():
    # Function-static variable... you could make this global, or whatever
    mtimes = check_for_modifications.mtimes
    for filename in _iter_module_files():
        try:
            mtime = os.stat(filename).st_mtime
        except OSError:
            continue

        old_time = mtimes.get(filename)
        if old_time is None:
            mtimes[filename] = mtime
            continue
        elif mtime > old_time:
            uwsgi.reload()
            return

check_for_modifications.mtimes = {} # init static

It's untested, but should work.

Answer 2

If you're configuring uwsgi with command arguments, pass --py-autoreload=1:

uwsgi --py-autoreload=1

If you're using a .ini file to configure uwsgi and using uwsgi --ini, add the following to your .ini file:

py-autoreload = 1

Answer 3

I am running uwsgi version 1.9.5 and the option

uwsgi --py-autoreload 1

works great

Answer 4

For development environment you can try using --python-autoreload uwsgi's parameter. Looking at the source code it may work only in threaded mode (--enable-threads).

Answer 5

import gevent.wsgi
import werkzeug.serving

@werkzeug.serving.run_with_reloader
def runServer():
    gevent.wsgi.WSGIServer(('', 5000), app).serve_forever()

(You can use an arbitrary WSGI server)

Answer 6

I am afraid that Flask is really too bare bones to have an implementation like this bundled by default.

Dynamically reloading code in production is generally a bad thing, but if you are concerned about a dev environment, take a look at this bash shell script http://aplawrence.com/Unixart/watchdir.html

Just change the sleep interval to whatever suits your needs and substitute the echo command with whatever you use to reload uwsgi. I run uwsgi un master mode and just send a killall uwsgi command.