Possible redis incompatibility?

[gedsic]

I set up pretalx according to the documentation, on Ubuntu 18.04 with a postgres database. With a pretalx user in /var/pretalx and a virtual environment in the right place. Setting up an event, opening the CfP worked, but uploaded files (e.g. logo image or resources in submissions) can't be viewed, nginx throws:

2018/11/21 19:43:27 [error] 1937#1937: *4 open() "/var/pretalx/data/media/testevent/img/testlogo.png" failed (2: No such file or directory), client: XXXXXXX, server: XXXXX, request: "GET /media/testevent/img/testlogo.png HTTP/1.1", host: "XXXXXX", referrer: "https://XXXXX/testevent/cfp"

Looking at the service logs, I seem to have a problem with the pretalx-worker service :

celery[3354]: [2018-11-21 14:28:33,821: INFO/MainProcess] Connected to redis://127.0.0.1:6379/2
celery[3354]: [2018-11-21 14:28:33,844: INFO/MainProcess] mingle: searching for neighbors
celery[3354]: [2018-11-21 14:28:34,855: INFO/MainProcess] mingle: all alone
celery[3354]: [2018-11-21 14:28:34,869: INFO/MainProcess] celery@XXXXXXXXXXX ready.
celery[3354]: [2018-11-21 14:28:35,240: CRITICAL/MainProcess] Unrecoverable error: AttributeError("'float' object has no attribute 'items'",)
celery[3354]: Traceback (most recent call last):
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/celery/worker/worker.py", line 205, in start
celery[3354]: self.blueprint.start(self)
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/celery/bootsteps.py", line 119, in start
celery[3354]: step.start(parent)
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/celery/bootsteps.py", line 369, in start
celery[3354]: return self.obj.start()
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/celery/worker/consumer/consumer.py", line 317, in start
celery[3354]: blueprint.start(self)
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/celery/bootsteps.py", line 119, in start
celery[3354]: step.start(parent)
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/celery/worker/consumer/consumer.py", line 593, in start
celery[3354]: c.loop(*c.loop_args())
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/celery/worker/loops.py", line 91, in asynloop
celery[3354]: next(loop)
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/kombu/asynchronous/hub.py", line 354, in create_loop
celery[3354]: cb(*cbargs)
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/kombu/transport/redis.py", line 1040, in on_readable
celery[3354]: self.cycle.on_readable(fileno)
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/kombu/transport/redis.py", line 337, in on_readable
celery[3354]: chan.handlerstype
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/kombu/transport/redis.py", line 724, in _brpop_read
celery[3354]: self.connection._deliver(loads(bytes_to_str(item)), dest)
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/kombu/transport/virtual/base.py", line 983, in _deliver
celery[3354]: callback(message)
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/kombu/transport/virtual/base.py", line 632, in _callback
celery[3354]: self.qos.append(message, message.delivery_tag)
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/kombu/transport/redis.py", line 149, in append
celery[3354]: pipe.zadd(self.unacked_index_key, time(), delivery_tag)
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/redis/client.py", line 2263, in zadd
celery[3354]: for pair in iteritems(mapping):
celery[3354]: File "/var/pretalx/venv/lib/python3.6/site-packages/redis/_compat.py", line 123, in iteritems
celery[3354]: return iter(x.items())
celery[3354]: AttributeError: 'float' object has no attribute 'items'
celery[3354]: ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
celery[3354]: ┃ ┏━━━━━━━━━━┓ This is pretalx v0.8.0 calling, running in production mode. ┃
celery[3354]: ┃ ┃ ┌─·──╮ ┃ ┃
celery[3354]: ┃ ┃ │ O │ ┃ Settings: ┃

After this error, the service restarts and runs into the error again shortly afterwards.

This seems to be related to celery/celery#5175. Explicitly pinning the redis version to 2.10.6 using pip install redis==2.10.6 leads to SSL connection errors from psycopg2:

celery[7205]: [2018-11-21 12:53:40,870: ERROR/ForkPoolWorker-1] Task pretalx.common.tasks.regenerate_css[e23dee6e-5a79-49b2-9e24-a5ef994a2f32] raised unexpected: OperationalError('SSL SYSCALL error: Bad file descriptor\n',)
celery[7205]: Traceback (most recent call last):
celery[7205]: File "/var/pretalx/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 85, in _execute
celery[7205]: return self.cursor.execute(sql, params)
celery[7205]: psycopg2.OperationalError: SSL SYSCALL error: Bad file descriptor
celery[7205]: The above exception was the direct cause of the following exception:
celery[7205]: Traceback (most recent call last):
celery[7205]: File "/var/pretalx/venv/lib/python3.6/site-packages/celery/app/trace.py", line 382, in trace_task

Is there a set of versions of all required python modules that is known to work?

[gedsic]

Nevermind, I figured out why uploaded images were not display and no mail got out. I had the wrong media directory in /etc/pretalx/pretalx.cfg. Serves me right for blindly trusting example configs.

So pinning redis 2.10.6 fixed the issue with the crashing worker.