How to fail the chain if it's sub task gives an exception

When you have a chain:

>>> c = a.s() | b.s() | c.s()
>>> res = c()
>>> res.get()

Calling the chain will generate unique id's for all of the task in the chain, send the messages and return the last result in the chain.

So when you do res.get() you are simple trying to retrieve the result of the last task in the chain.

It will also decorate the results with parent attributes, which you can traverse to get the progress of the chain:

>>> res                # result of c.s()
>>> res.parent         # result of b.s()
>>> res.parent.parent  # result of a.s()

If you want to check for errors along the way you can do:

def nodes(node):
    while node.parent:
        yield node
        node = node.parent
    yield node


values = [node.get(timeout=1) for node in reversed(list(nodes(res)))]
value = values[-1]

Actually I think you shouldn't be using raise here.

You're throwing an exception, when the documentation says you shouldn't, you might want to just use err.retry and not raise err.retry.