celery worker only imports tasks when not detached

Question

I'm trying to get my django app to submit tasks to a celery worker and it's succeeding when the worker is run attached. As soon as I add the --detach the tasks are failing to be registered.

[2020-10-26 04:09:33,159: ERROR/MainProcess] Received unregistered task of type 'devapp.tasks.create_random_files'.
The message has been ignored and discarded.

Did you remember to import the module containing this task?
Or maybe you're using relative imports?

Please see
http://docs.celeryq.org/en/latest/internals/protocol.html
for more information.

The full contents of the message body was:
'[[20, "blah", 5120], {}, {"callbacks": null, "errbacks": null, "chain": null, "chord": null}]' (93b)
Traceback (most recent call last):
  File "/pysite/project/venv/lib/python3.6/site-packages/celery/worker/consumer/consumer.py", line 562, in on_task_received
    strategy = strategies[type_]
KeyError: 'devapp.tasks.create_random_files'

In my tasks.py I have

import os
import string
import subprocess
from celery import shared_task, task

@shared_task(name='devapp.tasks.create_random_files')
def create_random_files(total,filename,size):
    for i in range(int(total)):
        filenum = str(i).zfill(5)
        rnd_filename = '/brdis/{}-{}'.format(filenum,filename)
        with open(rnd_filename, 'wb') as f:
            f.write(os.urandom(size))
            f.close
    return '{} random files created'.format(total)

and in my views.py I have

from django.shortcuts import render
from django.http import HttpResponse

from django.contrib import messages
from django.views.generic import TemplateView
from django.views.generic.list import ListView
from django.views.generic.edit import FormView
from django.shortcuts import redirect

from .forms import CreateRandomFilesForm, GetFileListForm, ClamScanFileForm
from .tasks import create_random_files, clamscanfile

class ClamScanFileView(FormView):
    template_name = 'devapp/clamscan_file.html'
    form_class = ClamScanFileForm

    def form_valid(self, form):
        filename = form.cleaned_data.get('filename')
        clamscanfile.delay(filename)
        messages.success(self.request, 'We are scanning your file!s Wait a moment and refresh this page.')
        return redirect('files_list')

I understand that it may be relative imports(something else i need to get my head round) but I don't understand why adding the --detach to the celery worker command produces this error:

celery -A project worker -E --loglevel=INFO --logfile=/var/log/celery/celeryd.log --pidfile=/var/run/celery/celeryd.pid

works fine but...

celery -A project worker -E --loglevel=INFO --logfile=/var/log/celery/celeryd.log --pidfile=/var/run/celery/celeryd.pid --detach

starts the worker but doesn't register the tasks?

Any help appreciated.

FWIW

celery report

software -> celery:4.4.7 (cliffs) kombu:4.6.11 py:3.6.8
            billiard:3.6.3.0 py-amqp:2.6.1
platform -> system:Linux arch:64bit, ELF
            kernel version:3.10.0-1127.19.1.el7.x86_64 imp:CPython
loader   -> celery.loaders.default.Loader
settings -> transport:amqp results:disabled

Answer 1

This is a bug with 4.4.7. Downgrading to 4.4.6 or upgrading to 5 should fix it.

https://github.com/celery/celery/issues/6370