Check tasks will be automatically picked up in case of outage

[filipeximenes]

In case of outage make sure Celery will pick up the tasks that were supposed to run while the system was off (if this makes sense in your business logic).

Bad:

# Messages for some tasks won't be sent if the outage lasts one day
for task in Tasks.objects.filter(due_to=today):
    send_messages()

Better:

for task in Tasks.objects.filter(due_to__lte=today, sent=False):
   send_messages()