celery.exceptions.NotRegistered

[alukach]

[2017-08-09 10:49:23,338: ERROR/MainProcess] Pool callback raised exception: Task of kind 'msg.email_err' never registered, please make sure it's imported.
Traceback (most recent call last):
  File "/Users/alukach/.virtualenvs/export-worker/lib/python3.6/site-packages/kombu/utils/objects.py", line 42, in __get__
    return obj.__dict__[self.__name__]
KeyError: 'type'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/alukach/.virtualenvs/export-worker/lib/python3.6/site-packages/billiard/pool.py", line 1747, in safe_apply_callback
    fun(*args, **kwargs)
  File "/Users/alukach/.virtualenvs/export-worker/lib/python3.6/site-packages/celery/worker/request.py", line 366, in on_failure
    self.id, exc, request=self, store_result=self.store_errors,
  File "/Users/alukach/.virtualenvs/export-worker/lib/python3.6/site-packages/celery/backends/base.py", line 168, in mark_as_failure
    self._call_task_errbacks(request, exc, traceback)
  File "/Users/alukach/.virtualenvs/export-worker/lib/python3.6/site-packages/celery/backends/base.py", line 174, in _call_task_errbacks
    if arity_greater(errback.type.__header__, 1):
  File "/Users/alukach/.virtualenvs/export-worker/lib/python3.6/site-packages/kombu/utils/objects.py", line 44, in __get__
    value = obj.__dict__[self.__name__] = self.__get(obj)
  File "/Users/alukach/.virtualenvs/export-worker/lib/python3.6/site-packages/celery/canvas.py", line 490, in type
    return self._type or self.app.tasks[self['task']]
  File "/Users/alukach/.virtualenvs/export-worker/lib/python3.6/site-packages/celery/app/registry.py", line 19, in __missing__
    raise self.NotRegistered(key)
celery.exceptions.NotRegistered: 'msg.email_err'

This occurs when a task experiences an exception and has an errback/link_error. For whatever reason, it attempts to run the task right then and there (as opposed to scheduling it in the queues). This is problematic if the errback is for a task not available in the worker's codebase. For whatever reason, this does not seem to occur in tasks that are run within a chord. See celery/kombu#4022.