Implement Event Streaming

[Lachstec]

The current version uses basic python message queues as exchange medium between siblings. Although it was convenient for the proof of concept, a more robust event streaming platform would be valuable.

TODO

• [x] Add a common Interface for Event / Message Brokers
• [x] Add Settings for Kafka configuration
• [x] Add Settings for RabbitMQ configuration
• [x] Implement a client for using Rabbit MQ as a Event / Message Broker
• [x] Implement a client for using Kafka as a Event / Message Broker
• [ ] Update digsinet to use an instance of the interface
• [ ] Testing

[S-Schickentanz]

Interface Design:

• init(config, channels: str, logger)
• publish(channel: str, value),
• poll(channel: str, timeout),
• subscribe(channel: str),
• get_sibling_channels(),
• new_sibling_channel(channel: str),
• close()

[Lachstec]

I made a branch and added the interface as described here. Feel free to make changes to it as you see fit.

[Lachstec]

It could be useful to factor out the sibling creation into a separate module / class / whatever. The creation would get a bit more specific to the underlying message broker and it could get messy if that is implemented in the main file.

[srieger1]

@Lachstec good point... that's somehow what I meant when I said, that it might be interesting to have both, a message queue (like Rabbit) for tasks (e.g., creation and control of siblings) and an event-streaming (like Kafka) for state updates and synchronization. However, this increases complexity and maybe we don't want/need that.