Handle requests to /

[mrwacky42]

This lets us do health checks against the exporter without having to
collect all the metrics.

For now, just print the version.

[moznion]

@mrwacky42
Thank you for your patch. It looks nice.
I have a question about this; in Prometheus, is path of the route (i.e. /) default to be used health checking?

[mrwacky42]

@moznion - I'm not sure if there is a standard. at $WORK, we use Consul for Prometheus service discovery. For other exporters, we just GET / to see if it is working for the Consul servic health check.
The best I can find is https://prometheus.io/docs/instrumenting/writing_exporters/#landing-page
I've added another commit to make it slightly more useful.

[moznion]

@mrwacky42
Thank you!

In my opinion, I think it is not explicit that the / represents a health check. For example, how about using /health instead?

[mrwacky42]

Sure. This patch doesn't really directly have anything to do with healthchecks other than allowing me to make a query to a different route than /metrics.

HandleFunc("/",..) already serves any request besides /metrics, including /health or /mrwacky42..

[moznion]

Thank you! Merged this feature.