I have a project that will be multiple, independent programs that network and message to each other. The connections between the modules will be tuned to the particular data types and requirements (size, latency, etc). But, control of the whole allocation needs some sort of ‘control plane’ for the setup, configuration, and control of all the programs. A message bus seems the right thing to send notices and updates around the whole distributed application.
I’m thinking some pub/sub system. Some criteria are:
- provides asynchronous notifications and status between network distributed programs
- low volume: after setup, messages will be rare
- light weight: both the clients and servers needs to be small and simple
- easy protocol: I’m not building a mission critical infrastructure here
- don’t need message ordering
- reliability and non-duplication would be good
- doesn’t require a ‘cloud service’: there are notification services that could be used but that should be an option and not a requirement
First candidate is MQTT. MQTT is simple-ish. Has lots of clients (like Eclipse/Paho and Mosquitto) and has several hardened brokers (Mosquitto, Moquette, Mosca, HiveMQ, and even multi-protocol servers like Apollo or [AMQP]). Conceptually a good simple and good model but there are gottchas in most of the clients and the brokers tend to be heavier than I need.
WAMP (Web Application Messaging Protocol) is another possibility. It is built around websockets but it basicily just needs a reliable connection (TCP). WAMP provides both pub/sub and RPC communication patterns which might be useful. It only moves JSON messages (text only) although it can use MsgPack for compressed/compacted messages. For a control plane message system, I don’t think I need binary so that is not a required feature.
Now, thinking about it, firewalls will always be a problem when running a centralized message service. If the distributed application is started on a tablet, it will start other components both locally (inside the firewall) and remotely (outside the firewall). If the message server is started with the application inside the firewall, any component outside the firewall would have problems connecting back to the ‘control plane’ server.
More discussion to come.