It seems like you have deviated from the standard install by setting up separate containers for Redis and Postgres, so I’m afraid I don’t have an out of the box answer for you. How did you configure the Redis settings within Discourse?
Another thing - I do see redis:4-alpine. I’m afraid you’ll need to move to a newer version of Redis since Discourse requires version 6.20 or higher. I don’t think this is the cause of your issue though.