[meta] Document environment variables in Sampling

[pellared]

I think we should also document setting the environment variable in a top-level section in this guide. That can be especially helpful for development since you can just use the default, but then have production do something different.

Originally posted by @cartermp in #3318 (review)

Also #3318 (comment)

---

(edit by @svrnm)

Tracking:

• C++
• .NET
• Erlang/Elixir
• Java
• JavaScript
• PHP
• Python
• Ruby
• Rust
• Swift

[pellared]

Resource: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/configuration/sdk-environment-variables.md

We should also probably call out that using trace.WithSampler overrides the env vars.

[svrnm]

is this only a go thing?

[pellared]

IMO not only Go. I think that the default value is wrongly defined in other languages. And also I think the clarification is needed for all languages.

[svrnm]

Ok. I removed the "Go" from the title :)

[svrnm]

@pellared turning this into a meta issue since it is relevant for all languages

[nerudadhich]

Hi @svrnm, I would like to start working on this. Will start from Java first.
Do we have any ideal format that we need to follow for this ? Any example from existing one's ?

[svrnm]

Hi @svrnm, I would like to start working on this. Will start from Java first. Do we have any ideal format that we need to follow for this ? Any example from existing one's ?

Apologies for the late reply, I was out of office. We currently have #4199 open, so it might need that to be closed before we can add some words about variables. You can review that PR if you like and create a follow up when merged.