PUB-SUB using ZeroMQ, used Redis to persist tasks/messages.

• Redis
• Python 3

$ cd <project-dir>
$ export PYTHONPATH="$PYTHONPATH:." # . corresponds to current directory(project-dir).
$ virtualenv -p python3 .env        # Create virtual environment.
$ pip install -r requirements.txt   # Install dependencies.

And then publisher can be started as -

$ python publisher.py

and subscriber(s) can be started as -

$ python subscriber.py

• Traditional Publisher-Subscriber model.
• A subscriber can subscribe to multiple topics. Each subscriber is identified by unique id(alphanumeric).
• Publisher can specify TTL(Time-to-live) while publishing a message to particular topic. So a message(with ttl = t secconds) will expire after t seconds.
• A message is published on a topic(T) will be delivered to each subscriber of that topic(T) exactly once.
• If a subscriber goes down for a duration(D), then all the pending messages(with TTL > D) will be delivered to that subscriber once it comes back alive after duration(D).
• Publisher & subscriber(s) needs to connect to Redis.
• Each & every subscriber must be assigned a unique id.