Saving a celery task (for re-running) in database - django

Question

Our workflow is currently built around an old version of celery, so bear in mind things are already not optimal. We need to run a task and save a record of that task run in the database. If that task fails or hangs (it happens often), we want to re run, exactly as it was run the first time. This shouldn't happen automatically though. It needs to be triggered manually depending on the nature of the failure and the result needs to be logged in the DB to make that decision (via a front end).
How can we save a complete record of a task in the DB so that a subsequent process can grab the record and run a new identical task? The current implementation saves the path of the #task decorated function in the DB as part of a TaskInfo model. When the task needs to be rerun, we have a get_task() method on the TaskInfo model that gets the path from the DB, imports it using getattr, and another rerun() method that runs the task again with *args, **kwargs (also saved in the DB).
Like so (these are methods on the TaskInfo model instance):
def get_task(self):
"""Returns the task's decorated function, which can be delayed."""
module_name, object_name = self.path.rsplit('.', 1)
module = import_module(module_name)
task = getattr(module, object_name)
if inspect.isclass(task):
task = task()
# task = current_app.tasks[self.path]
return task
def rerun(self):
"""Re-run the task, and replace this one.
- A new task is scheduled to run.
- The new task's TaskInfo has the same parent as this TaskInfo.
- This TaskInfo is deleted.
"""
args, kwargs = self.get_arguments()
celery_task = self.get_task()
celery_task.delay(*args, **kwargs)
defaults = {
'path': self.path,
'status': Status.PENDING,
'timestamp': timezone.now(),
'args': args,
'kwargs': kwargs,
'parent': self.parent,
}
TaskInfo.objects.update_or_create(task_id=celery_task.id, defaults=defaults)
self.delete()
There must be a cleaner solution for saving a task in the DB to rerun later, right?

Answer 1

The latest version of Celery (4.4.0) included a param extended_result. You can set it to True, then the table (it is named celery_taskmeta by default) in the Result Backend Database will store the args and kwargs of the task.
Here is a demo:
app = Celery('test_result_backend')
app.conf.update(
broker_url='redis://localhost:6379/10',
result_backend='db+mysql://root:passwd#localhost/celery_toys',
result_extended=True
)
#app.task(bind=True, name='add')
def add(self, x, y):
self.request.task_name = 'add' # For saving the task name.
time.sleep(5)
return x + y
With the task info recorded in MySQL, you are able to re-run your task easily.