MQTT notification: retry failing notifications in the CB->MQTT broker segment

[fgalan]

Is your feature request related to a problem / use case? Please describe.

MQTT notification delivery reliability

Describe the solution you'd like

MQTT notifications follow this schema:

CB -(1)-> MQTT broker -(2)-> subscribed clients

while we can have delivery reliability at (2) using MQTT QoS 2, currently the (1) segment is somehow "weak". If the notifcation publish message fails, CB doesn't retries it.

Thus, a CB->MQTT retry mechanism could be implemented. It could be based in some subscription configuration (e.g. notification.mqtt[Custom].retries).

Describe alternatives you've considered

None

Describe why you need this feature

• To improve or simplify an scenario.

Additional information

It should be easy to accomplish if the MQTT libreary we are using provides some kind on callback handler. If the callback is called with a "error" status, then retry until the desired limit.