How to run a function periodically with Flask and Celery?

Question

I have a flask app that roughly looks like this:

app = Flask(__name__)
@app.route('/',methods=['POST'])
def foo():
   data = json.loads(request.data)
   # do some stuff

   return "OK"

Now in addition I would like to run a function every ten seconds from that script. I don't want to use sleep for that. I have the following celery script in addition:

from celery import Celery
from datetime import timedelta
celery = Celery('__name__')

CELERYBEAT_SCHEDULE = {
    'add-every-30-seconds': {
        'task': 'tasks.add',
        'schedule': timedelta(seconds=10)
    },
}



@celery.task(name='tasks.add')
def hello():
    app.logger.info('run my function')

The script works fine, but the logger.info is not executed. What am I missing?

Answer 1

Do you have Celery worker and Celery beat running? Scheduled tasks are handled by beat, which queues the task mentioned when appropriate. Worker then actually crunches the numbers and executes your task.

celery worker --app myproject--loglevel=info
celery beat --app myproject

Your task however looks like it's calling the Flask app's logger. When using the worker, you probably don't have the Flask application around (since it's in another process). Try using a normal Python logger for the demo task.