Have a look at the Postgres filter for the Envoy proxy: [1] (blog announcement post).
While it's not capturing as of today query performance, it collects notable telemetry for Postgres in exactly the way you mention: just because the traffic flows through it, making it a way to collect data "for free" and definitely without taking any resources from the upstream database.
It can also offload SSL from Postgres. The filter could be extended for other use cases.
Disclaimer: my company developed this plugin for Envoy with the help of Envoy's awesome community.
While it's not capturing as of today query performance, it collects notable telemetry for Postgres in exactly the way you mention: just because the traffic flows through it, making it a way to collect data "for free" and definitely without taking any resources from the upstream database.
It can also offload SSL from Postgres. The filter could be extended for other use cases.
Disclaimer: my company developed this plugin for Envoy with the help of Envoy's awesome community.
[1]: https://www.cncf.io/blog/2020/08/13/envoy-1-15-introduces-a-...