bridge/uds: confirm protocol design for unix-socket producers

[lucab]

This exporter currently defines a unix-socket protocol, which must me stabilized in order to be implemented by relevant producers.

The current protocol is by the design the simplest that I could imagine. It just expects producers to spit out Prometheus textual format to each new client connection, and then close the connection.

This waits on @pgier and @simonpasquier for protocol design review.

[lucab]

Once this is resolved, it will unblock https://github.com/coreos/zincati/issues/74.

[simonpasquier]

:+1: I don't think we need anything more fancy than a transparent proxy between the producer and Prometheus.

[lucab]

This is even a bit less than a transparent proxy, as it doesn't speak HTTP over the unix-domain socket. That is intentional, in order to avoid:

• a requirement on producers to implement a full HTTP stack
• the quirkness of HTTP-over-UDS (what's the hostname? how is the uds path specified in the URL?)

[simonpasquier]

Yes I didn't mean proxy in the sense of network proxy.

[lucab]

Nothing major came up in a few month of usage, sticking to this. Closing.