With Celery Canvas, what is the difference between chord() and chain(group(), task)

Question

We're implementing a workflow with Celery. First we need to run some tasks in parallel, and when they are all finished we need to run a single task.

It seems we can use chord, or group and chain:

chord(tasks, task)

vs

group(tasks) | task

What is the exact difference between those two? They seem to do the same thing.

Answer 1

The Canvas docs say:

Chaining a group together with another task will automatically upgrade it to be a chord:

 >>> c3 = (group(add.s(i, i) for i in xrange(10)) | xsum.s())
>>> res = c3()
>>> res.get()
90