[mosquitto-dev] Thinking about health checks for a MQTT client running i

[Steve Prior <sprior@xxxxxxxxxxxx>]

I have a bunch of services running in containers which are "pure" MQTT 
clients - the service subscribes to MQTT topics and when it receives a 
message it performs some action.  The service doesn't have an http 
service or a tcp port it's listening on - all its connections are outbound.

I'm trying to think about what would make sense as a health check for 
such an application.   I'm not very excited about adding a http listener 
just as a health check endpoint and nothing else. Sending a MQTT message 
to a special health check topic that the service replies to may work but 
I'm not sure there aren't problems there too.

So I'm curious what (if anything) others are doing.  Another thought I 
had is could it be possible to query the mosquitto server about the 
health of the client service's connection to it - the health check is 
does the mosquitto server have a current ping for the MQTT client?  It's 
just a little weird to ask a third party (the mosquitto server) about 
the health of one of it's clients, but maybe not wrong.  I'm sure that 
it gets a little tricky to have that kind of health check know the 
client id which would be needed to query in the mosquitto server unless 
the mqtt client service uses a hardcoded client id (which wouldn't be 
desireable).

Thoughts?

Steve