standardize on exclusion functionality for HTTP instrumentations

[toumorokoshi]

There's a few PRs on the Python side to introduce denylists of specific HTTP paths and hosts:

open-telemetry/opentelemetry-python#670

Is this an area that we should consider incorporating into conventions? I feel like it would be great to work on a standard that works for a variety of scenarios around http span denylist, and to ensure similar functionality is provided across languages.

[arminru]

There was some discussion regarding that a year ago on #173 but no concrete proposal.

[toumorokoshi]

@arminru got it. Thanks for the information.

I'll at least start gathering some information, and maybe others came chime into the discussion.

From the python perspective, our excludes currently support two matches:

• exclude by host, which looks at the hostname and will exclude based on substring match
• exclude by path, which looks at the fully qualified path prefix and excludes based on that.

Example: https://github.com/open-telemetry/opentelemetry-python/tree/master/ext/opentelemetry-ext-django

Currently they are namespaced by instrumentation, although I believe values could most likely be shared:

• OPENTELEMETRY_PYTHON_{NAME}_EXCLUDED_HOSTS
• OPENTELEMETRY_PYTHON_{NAME}_EXCLUDED_PATHS

[bogdandrutu]

@toumorokoshi please make sure you DON'T use blacklists use alternatives like exclude or other options.