Celery auto reload on ANY changes

OrangeTux’s solution didn’t work out for me, so I wrote a little Python script to achieve more or less the same. It monitors file changes using inotify, and triggers a celery restart if it detects a IN_MODIFY, IN_ATTRIB, or IN_DELETE.

#!/usr/bin/env python
"""Runs a celery worker, and reloads on a file change. Run as ./run_celery [directory]. If
directory is not given, default to cwd."""
import os
import sys
import signal
import time

import multiprocessing
import subprocess
import threading

import inotify.adapters


CELERY_CMD = tuple("celery -A amcat.amcatcelery worker -l info -Q amcat".split())
CHANGE_EVENTS = ("IN_MODIFY", "IN_ATTRIB", "IN_DELETE")
WATCH_EXTENSIONS = (".py",)

def watch_tree(stop, path, event):
    """
    @type stop: multiprocessing.Event
    @type event: multiprocessing.Event
    """
    path = os.path.abspath(path)

    for e in inotify.adapters.InotifyTree(path).event_gen():
        if stop.is_set():
            break

        if e is not None:
            _, attrs, path, filename = e

            if filename is None:
                continue

            if any(filename.endswith(ename) for ename in WATCH_EXTENSIONS):
                continue

            if any(ename in attrs for ename in CHANGE_EVENTS):
                event.set()


class Watcher(threading.Thread):
    def __init__(self, path):
        super(Watcher, self).__init__()
        self.celery = subprocess.Popen(CELERY_CMD)
        self.stop_event_wtree = multiprocessing.Event()
        self.event_triggered_wtree = multiprocessing.Event()
        self.wtree = multiprocessing.Process(target=watch_tree, args=(self.stop_event_wtree, path, self.event_triggered_wtree))
        self.wtree.start()
        self.running = True

    def run(self):
        while self.running:
            if self.event_triggered_wtree.is_set():
                self.event_triggered_wtree.clear()
                self.restart_celery()
            time.sleep(1)

    def join(self, timeout=None):
        self.running = False
        self.stop_event_wtree.set()
        self.celery.terminate()
        self.wtree.join()
        self.celery.wait()
        super(Watcher, self).join(timeout=timeout)

    def restart_celery(self):
        self.celery.terminate()
        self.celery.wait()
        self.celery = subprocess.Popen(CELERY_CMD)


if __name__ == '__main__':
    watcher = Watcher(sys.argv[1] if len(sys.argv) > 1 else ".")
    watcher.start()

    signal.signal(signal.SIGINT, lambda signal, frame: watcher.join())
    signal.pause()

You should probably change CELERY_CMD, or any other global variables.

Celery --autoreload doesn’t work and it is deprecated.

Since you are using django, you can write a management command for that.
Django has autoreload utility which is used by runserver to restart WSGI server when code changes.

The same functionality can be used to reload celery workers. Create a seperate management command called celery. Write a function to kill existing worker and start a new worker. Now hook this function to autoreload as follows.

import shlex
import subprocess

from django.core.management.base import BaseCommand
from django.utils import autoreload


def restart_celery():
    cmd = 'pkill celery'
    subprocess.call(shlex.split(cmd))
    cmd = 'celery worker -l info -A foo'
    subprocess.call(shlex.split(cmd))


class Command(BaseCommand):

    def handle(self, *args, **options):
        print('Starting celery worker with autoreload...')

        # For Django>=2.2
        autoreload.run_with_reloader(restart_celery) 

        # For django<2.1
        # autoreload.main(restart_celery)

Now you can run celery worker with python manage.py celery which will autoreload when codebase changes.

This is only for development purposes and do not use it in production. Code taken from my other answer here.

This is the way I made it work in Django:

# worker_dev.py (put it next to manage.py)
from django.utils import autoreload


def run_celery():
    from projectname import celery_app

    celery_app.worker_main(["-Aprojectname", "-linfo", "-Psolo"])


print("Starting celery worker with autoreload...")
autoreload.run_with_reloader(run_celery)

Then run python worker_dev.py. This has an advantage of working inside docker container.

You can use watchmedo

pip install watchdog

Start celery worker indirectly via watchmedo

watchmedo auto-restart --directory=./ --pattern=*.py --recursive -- celery worker --app=worker.app --concurrency=1 --loglevel=INFO

More detailed

I used watchdog watchdemo utility, it works great but for some reason the PyCharm debugger was not able to debug the subprocess spawned by watchdemo.

So if your project has werkzeug as dependency, you can use the werkzeug._reloader.run_with_reloader function to autoreload celery worker on code change. Plus it works with PyCharm debugger.

"""
Filename: celery_dev.py
"""

import sys

from werkzeug._reloader import run_with_reloader

# this is the celery app path in my application, change it according to your project
from web.app import celery_app


def run():
    # create copy of "argv" and remove script name
    argv = sys.argv.copy()
    argv.pop(0)

    # start the celery worker
    celery_app.worker_main(argv)


if __name__ == '__main__':
    run_with_reloader(run)

Sample PyCharm debug configuration.

NOTE:

This is a private werkzeug API and is working as of Werkzeug==2.0.3. It may stop working in future versions. Use at you own risk.

This is a huge adaptation from Suor’s code.

I made a custom Django command which can be called like this:

python manage.py runcelery

So, every time the code changes, celery’s main process is gracefully killed and then executed again.

Change the CELERY_COMMAND variable as you wish.

# File: runcelery.py
import os
import signal
import subprocess
import time

import psutil
from django.core.management.base import BaseCommand
from django.utils import autoreload


DELAY_UNTIL_START = 5.0
CELERY_COMMAND = 'celery --config my_project.celeryconfig worker --loglevel=INFO'


class Command(BaseCommand):

    help = ''

    def kill_celery(self, parent_pid):
        os.kill(parent_pid, signal.SIGTERM)

    def run_celery(self):
        time.sleep(DELAY_UNTIL_START)
        subprocess.run(CELERY_COMMAND.split(' '))

    def get_main_process(self):
        for process in psutil.process_iter():
            if process.ppid() == 0:  # PID 0 has no parent
                continue

            parent = psutil.Process(process.ppid())

            if process.name() == 'celery' and parent.name() == 'celery':
                return parent

        return

    def reload_celery(self):
        parent = self.get_main_process()

        if parent is not None:
            self.stdout.write('[*] Killing Celery process gracefully..')
            self.kill_celery(parent.pid)

        self.stdout.write('[*] Starting Celery...')
        self.run_celery()

    def handle(self, *args, **options):
        autoreload.run_with_reloader(self.reload_celery)

There was an issue in @AlexTT answer, I don’t know if I should comment on his answer of put this as an answer.

You can use watchmedo

pip install watchdog

Start celery worker indirectly via watchmedo

watchmedo auto-restart --directory=./ --pattern=*.py --recursive -- celery -A <app> worker --concurrency=1 --loglevel=INFO