Develop Reference

How to fix receiving unregistered task error - Celery

I am trying to establish a periodic task using Celery (4.2.0) and RabbitMQ (3.7.14) running with Python 3.7.2 on an Azure VM using Ubuntu 16.04. I am able to start the beat and worker and see the message get kicked off from beat to the worker but at this point I'm met with an error like so
[2019-03-29 21:35:00,081: ERROR/MainProcess] Received
unregistered task of type 'facebook-call.facebook_api'.
The message has been ignored and discarded.
Did you remember to import the module containing this task?
Or maybe you're using relative imports?
My code is as follows:
from celery import Celery
from celery.schedules import crontab
app = Celery('facebook-call', broker='amqp://localhost//')
#app.task
def facebook_api():
{function here}
app.conf.beat.schedule = {
'task': 'facebook-call.facebook_api',
'schedule': crontab(hour=0, minute =0, day='0-6'),
}
I am starting the beat and worker processes by using the name of the python file which contains all of the code
celery -A FacebookAPICall beat --loglevel=info
celery -A FacebookAPICall worker --loglevel=info
Again, the beat process starts and I can see the message being successfully passed to the worker but cannot figure out how to "register" the task so that it is processed by the worker.

I was able to resolve the issue by renaming the app from facebook-call to coincide with the name of the file FacebookAPICall
Before:
app = Celery('facebook-call', broker='amqp://localhost//'
After:
app = Celery('FacebookAPICall', broker='amqp://localhost//'
From reading the Celery documentation, I don't totally understand why the name of the app must also be the name of the .py file but that seems to do the trick.

Execute Celery's link_error callback on a separate queue/worker

I have 2 apps on 2 separate servers, let's call them A and B. Both apps have a Celery worker active, listening to separate queues (QueueA and QueueB).
Server B pushes a task to QueueB, using apply_async.
Here is server B's tasks:
#app.task(bind=True, queue="QueueB", name="name_on_server_A")
def taskForServerB():
# nothing is executed here
#app.task(bind=True)
def success(result):
print('Task succeeded')
#app.task(bind=True):
def failure(...):
print('task failed')
taskForServerB.s().apply_async(link=success.s(), link_error=failure.s())
On Server A, the task name_on_server_A receives the tasks and executes it. If it completes successfully, the task success is execute properly on ServerB, but it name_on_server_A fails, the task failure is not executed. Instead, Server A throws a NotRegisteredError for a task with name failure.
Is there something I am missing? How can I get the failure task to be executed on ServerB, where the first task is called from?

There are two issues here:
The route of task to the correct queue which you defined for name_on_server_A (with the queue assignment) - which is by the way something that is new for me (I'm using ROUTER in the celery config and route each task by it's name to the right queue.
when you define your celery app you might forgot to include the task failure so it unregister:
app = Celery(broker='amqp://', backend='...', include=['file1.py', 'file2.py', ..])

Celery worker disappeared without errors

I setup Celery with Django app and broker "Redis"
#task
def proc(product_id,url,did,did_name):
## some long operation here
#task
def Scraping(product_id,num=None):
if num:
num=int(num) ## this for i can set what count of subtasks run now
res=group([proc.s(product_id,url,did,dis[did]) for did in dis.keys()[:num]])()
result = res.get()
return sum(result)
First few subtasks run successful, but later any worker dissapears and new tasks are still in RECEIVED status. Because the worker which must operate it does not exist.
I setup minimal concurency and 2 workers in /etc/default/celeryd.
I monitor CPU and memory usage, no highload detected.
There are no errors in the Celery logs!!!
What's wrong?
[2015-12-19 04:00:30,131: INFO/MainProcess] Task remains.tasks.proc[fd0ec29c-436f-4f60-a1b6-3785342ac173] succeeded in 20.045763085s: 6
[2015-12-19 04:17:28,895: INFO/MainProcess] missed heartbeat from w2#server.domain.com
[2015-12-19 04:17:28,897: DEBUG/MainProcess] w2#server.domain.com joined the party
[2015-12-19 05:11:44,057: INFO/MainProcess] missed heartbeat from w2#server.domain.com
[2015-12-19 05:11:44,058: DEBUG/MainProcess] w2#server.domain.com joined the party
SOLUTION>>> --------------------------------------------------------------)))))
if you use django-celery and want use celery as daemon: no use app() http://docs.celeryproject.org/en/latest/userguide/application.html , instead you must setup your celery in /etc/default/celeryd direct to manage.py of your project as: CELERYD_MULTI="$CELERYD_CHDIR/manage.py celeryd_multi"
do not disable heartbeats!!!!!
for use celery with direct to manage.py need:
create arg. CELERY_APP="" in /etc/default/celeryd beacuse if you don't do it, beat will be make run-command with old argument "app".
add line: "export DJANGO_SETTINGS_MODULE="your_app.settings"" to celeryd config if you not use default settings

Celery + Redis losing connection

I have a very simple Celery task that runs a (long running) shell script:
import os
from celery import Celery
os.environ['CELERY_TIMEZONE'] = 'Europe/Rome'
os.environ['TIMEZONE'] = 'Europe/Rome'
app = Celery('tasks', backend='redis', broker='redis://OTHER_SERVER:6379/0')
#app.task(name='ct.execute_script')
def execute_script(command):
return os.system(command)
I have this task running on server MY_SERVER and I launch it from OTHER_SERVER where is also running the Redis database.
The task seems to run successfully (I see the result of executing the script on the filesystem) but the I always start getting the following error:
INTERNAL ERROR: ConnectionError('Error 111 connecting to localhost:6379. Connection refused.',)
What could it be? Why is it trying to contact localhost while I've set the Redis server to be redis://OTHER_SERVER:6379/0 and it works (since the task is launched)? Thanks

When you set the backend argument, Celery will use it as the result backend.
On your code, you tell Celery to use local redis server as the result backend.
You seen ConnectionError， because celery can't save the reult to local redis server.
You can disable result backend or start an local redis server or set it to OTHER_SERVER.
ref:
http://celery.readthedocs.org/en/latest/getting-started/first-steps-with-celery.html#keeping-results
http://celery.readthedocs.org/en/latest/configuration.html#celery-result-backend

Celery / RabbitMQ / Django not running tasks

I am hoping someone can help me as I've looked on Stack Overflow and cannot find a solution to my problem. I am running a Django project and have Supervisor, RabbitMQ and Celery installed. RabbitMQ is up and running and Supervisor is ensuring my celerybeat is running, however, while it logs that the beat has started and sends tasks every 5 minutes (see below), the tasks never actually execute:
My supervisor program conf:
[program:nrv_twitter]
; Set full path to celery program if using virtualenv
command=/Users/tsantor/.virtualenvs/nrv_env/bin/celery beat -A app --loglevel=INFO --pidfile=/tmp/nrv-celerybeat.pid --schedule=/tmp/nrv-celerybeat-schedule
; Project dir
directory=/Users/tsantor/Projects/NRV/nrv
; Logs
stdout_logfile=/Users/tsantor/Projects/NRV/nrv/logs/celerybeat_twitter.log
redirect_stderr=true
autorestart=true
autostart=true
startsecs=10
user=tsantor
; if rabbitmq is supervised, set its priority higher so it starts first
priority=999
Here is the output of the log from the program above:
[2014-12-16 20:29:42,293: INFO/MainProcess] beat: Starting...
[2014-12-16 20:34:08,161: INFO/MainProcess] Scheduler: Sending due task gettweets-every-5-mins (twitter.tasks.get_tweets)
[2014-12-16 20:39:08,186: INFO/MainProcess] Scheduler: Sending due task gettweets-every-5-mins (twitter.tasks.get_tweets)
[2014-12-16 20:44:08,204: INFO/MainProcess] Scheduler: Sending due task gettweets-every-5-mins (twitter.tasks.get_tweets)
[2014-12-16 20:49:08,205: INFO/MainProcess] Scheduler: Sending due task gettweets-every-5-mins (twitter.tasks.get_tweets)
[2014-12-16 20:54:08,223: INFO/MainProcess] Scheduler: Sending due task gettweets-every-5-mins (twitter.tasks.get_tweets)
Here is my celery.py settings file:
from datetime import timedelta
BROKER_URL = 'amqp://guest:guest#localhost//'
CELERY_DISABLE_RATE_LIMITS = True
CELERYBEAT_SCHEDULE = {
'gettweets-every-5-mins': {
'task': 'twitter.tasks.get_tweets',
'schedule': timedelta(seconds=300) # 300 = every 5 minutes
},
}
Here is my celeryapp.py:
from __future__ import absolute_import
import os
from django.conf import settings
from celery import Celery
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'app.settings')
app = Celery('app')
app.config_from_object('django.conf:settings')
app.autodiscover_tasks(lambda: settings.INSTALLED_APPS)
Here is my twitter/tasks.py:
from __future__ import absolute_import
import logging
from celery import shared_task
from twitter.views import IngestTweets
log = logging.getLogger('custom.log')
#shared_task
def get_tweets():
"""
Get tweets and save them to the DB
"""
instance = IngestTweets()
IngestTweets.get_new_tweets(instance)
log.info('Successfully ingested tweets via celery task')
return True
The get_tweets method never gets executed, however I know it works as I can execute get_tweets manually and it works fine.
I have spent two days trying to figure out why its sending due tasks, but not executing them? Any help is greatly appreciated. Thanks in advance.

user2097159 thanks for pointing me in the right direction, I was not aware I also must run a worker using supervisor. I thought it was either a worker or a beat, but now I understand that I must have a worker to handle the task and a beat to fire off the task periodically.
Below is the missing worker config for supervisor:
[program:nrv_celery_worker]
; Worker
command=/Users/tsantor/.virtualenvs/nrv_env/bin/celery worker -A app --loglevel=INFO
; Project dir
directory=/Users/tsantor/Projects/NRV/nrv
; Logs
stdout_logfile=/Users/tsantor/Projects/NRV/nrv/logs/celery_worker.log
redirect_stderr=true
autostart=true
autorestart=true
startsecs=10
user=tsantor
numprocs=1
; Need to wait for currently executing tasks to finish at shutdown.
; Increase this if you have very long running tasks.
stopwaitsecs = 600
; When resorting to send SIGKILL to the program to terminate it
; send SIGKILL to its whole process group instead,
; taking care of its children as well.
killasgroup=true
; if rabbitmq is supervised, set its priority higher
; so it starts first
priority=998
I then reset the RabbitMQ queue. Now that I have both the beat and worker programs managed via supervisor, all is working as intended. Hope this helps someone else out.

You need to a start both a worker process and a beat process. You can create separate processes as described in tsantor's answer, or you can create a single process with both a worker and a beat. This can be more convenient during development (but is not recommended for production).
From "Starting the scheduler" in the Celery documentation:
You can also embed beat inside the worker by enabling the workers -B option, this is convenient if you’ll never run more than one worker node, but it’s not commonly used and for that reason isn’t recommended for production use:
$ celery -A proj worker -B
For expression in Supervisor config files see https://github.com/celery/celery/tree/master/extra/supervisord/ (linked from "Daemonization")