Redis-backed queues do not consume further messages once a queue is empty

[lmorandini]

Fission/Kubernetes version

fission version
client:
  fission/core:
    BuildDate: "2023-11-30T15:47:54Z"
    GitCommit: 9b57f1f2
    Version: v1.20.0
server:
  fission/core:
    BuildDate: "2023-11-30T15:47:54Z"
    GitCommit: 9b57f1f2
    Version: v1.20.0
kubectl version
Client Version: v1.28.4
Kustomize Version: v5.0.4-0.20230601165947-6ce0bf390ce3
Server Version: v1.23.8

Kubernetes platform (e.g. Google Kubernetes Engine)
OpenStack

Describe the bug
It looks like Redis-backed queues are no longer listened to once a list is empty (hence deleted from Redis, since it has no concept of an empty list).

To Reproduce

Pre-requirements:

• Redis installed in the cluster (version 7.0.12)
• Keda installed in the cluster (version 2.0)

Create a producer.py script:

import redis, datetime
from flask import current_app

def main():
    rdb = redis.StrictRedis(host='redis-headless.ot-operators.svc.cluster.local')
    rdb.lpush('redisbug-topic', f'Time: {datetime.datetime.now().isoformat()}')
    current_app.logger.info(f'Message sent')
    return 'Message sent\n'

Create a consumer.py script:

from flask import request
from flask import current_app

def main():
    current_app.logger.info(f'Message consumed: {request.data}')
    return f'Message comsumed\n'

Test setup:

fission function create --name producer --env python --code producer.py
fission function create --name consumer --env python --code consumer.py
fission route create --url /consumer --function consumer --createingress

On two different shells start log observers:

fission function log -f --name producer
fission function log -f --name consumer

Execute:

fission function test --name producer
fission function test --name producer
fission function test --name producer
fission function test --name producer

The producer function log should now show the messages being produced.

Let's create a trigger to consume the messages:

fission mqtrigger create --name redisbug\
   --function consumer\
   --mqtype redis\
   --mqtkind keda\
   --topic redisbug-topic\
   --resptopic redisbug-response-topic\
   --errortopic redisbug-error-topic\
   --maxretries 3\
   --metadata address=redis-headless.ot-operators.svc.cluster.local:6379\
   --metadata listLength=10\
   --metadata listName=redisbug-topic

Now the consumer function log should show the messages being consumed.

Let's add some more messages:

fission function test --name producer
fission function test --name producer
fission function test --name producer
fission function test --name producer

The logs should show the messages being produced, but NO message is consumed.

Deleting and recreating the trigger fixes the issue:
fission mqtrigger delete --name redisbug

Expected result
The messaged should be consumed even after the Redis list is emptied.

Actual result
No messages are further consumed.

Screenshots/Dump file

[sanketsudake]

Slack thread reference: https://fissionio.slack.com/archives/C3LUX6BBP/p1701415694875969

[vladrad]

Hello! I have this exact issue and was wondering if you found the solution?

[lmorandini]

No. I just switched to Kafka-backed queues.