North-South message bus ADR

[jpwhitemn]

Per the Kamakura planning meeting (Nov 21), it was resolved that an ADR on how to achieve north-south communications was the goal for this Kamakura release cycle. A stretch goal would be to implement the subscription capability outlined in an ADR in DS/DS SDKs

Command service – second order priority to get commands from external via MQTT (GRPC/RPC, AMQP in future). MQTT only to start
Device service – start with receiving commands from command service via bus

Message bus provides means for:

• Guaranteed delivery and better QoS where needed
• Messaging preferred in many use cases
  Would require (and could be done in phases)
• Command service to receive and relay messages
• DS to receive/process messages
  Other questions
• Would AS need message bus acknowledgement
• Rules engine to call message bus or REST option?
• What about other services using message bus (support notifications, scheduler, etc.)