celery chain doesn't propagate errors

chainfail.py

#!/usr/bin/env python

#
# Good reading:
# http://stackoverflow.com/questions/12660994/how-to-fail-the-chain-if-its-sub-task-gives-an-exception
#
#

# Celery instance
def create_celery():
    from celery import Celery
    celery = Celery()
    celery.conf.update(
        BROKER_URL='amqp://guest@localhost',
        CELERY_RESULT_BACKEND='amqp',
        CELERY_TASK_RESULT_EXPIRES=20
    )
    return celery


celery = create_celery()


#
# Task definitions
#
@celery.task(name='add1')
def add1(x):
    return x + 1


@celery.task(name='mult2')
def mult2(x):
    return x * 2


@celery.task(name='fails')
def fails(x):
    raise AssertionError("This task failed!")


def create_chain(fail=False):
    from celery import chain
    tasks = [add1.s(), mult2.s()]
    if fail:
        tasks.insert(1, fails.s())
    return chain(*tasks)


#
# Publisher
#
def log(result, indent=0, prefix=""):
    spaces = indent * " "
    print spaces, prefix, "result=%s, .status=%s, .results=%s" % (repr(result), result.status, result.result)
    if result.parent:
        log(result.parent, indent=indent+4, prefix="parent")

def publisher(fail=False):
    from time import sleep
    workflow = create_chain(fail)
    result = workflow.apply_async(args=[3])


    while not result.ready():
        log(result)
        sleep(1)
    log(result)
    assert result.result == 8


if __name__ == '__main__':
    from argparse import ArgumentParser
    parser = ArgumentParser()
    parser.add_argument('--fail', dest='fail', action='store_true')
    options = parser.parse_args()
    publisher(fail=options.fail)