You can pass along timing data from every aspect of the request [1] currently there are approximately 20 events supported. You can also send over just about anything that can be stored within an HAProxy variable / header through a tag. Here's an example configuration for HAProxy (simple) [2] (advanced) [3] and the OpenTracing specific configuration (simple) [4] (advanced) [5]. I've included both simple and advanced configurations.

[1] https://github.com/haproxy/haproxy/blob/master/addons/ot/REA...

[2] https://github.com/haproxy/haproxy/blob/master/addons/ot/tes...

[3] https://github.com/haproxy/haproxy/blob/master/addons/ot/tes...

[4] https://github.com/haproxy/haproxy/blob/master/addons/ot/tes...

[5] https://github.com/haproxy/haproxy/blob/master/addons/ot/tes...

Yea, it's pretty flexible and you can attach any additional metadata that you want (e.g. app version info, user name).

My question is what conversation has there been re: Opentelemetry, the successor to OT

It sounds like ot is still in beta (but it's a little confusing that they're 1.0 but it has a message saying they're in beta on their main page).

It looks like it's being adopted by a few larger app monitoring products, wondering if datadog will follow suit or if they will stick with open tracing and their custom implementations for logging and metrics. I assume they will support ingestion from ot at some point though. It sounds neat tho, will definitely read up on it more.