Downgrade System.Diagnostics.DiagnosticSource to v6 and add a check if OpenTelemetry instrumentation can be used

[pmaytak]

Fixes #4456. An alternative to #4486 solution.

Changes proposed in this request

• Downgrade System.Diagnostics.DiagnosticSource to v6, which is the same version as what Azure Functions runtime uses.
• Catching error when instantiating Open Telemetry fails (means it's not available in that environment) and using null telemetry implementation instead.
• See issue for more details.

Testing

• Unit tests pass.
• Tested with a dev app.
• Also tested that Activity code from 5dc10b2 works.

[gladjohn]

thanks for referencing this issue, so even downgrading still causes some issues?

[pmaytak]

thanks for referencing this issue, so even downgrading still causes some issues?

Currently downgrading doesn't cause issues. However, it's not future-proof if we ever need newer APIs. Additionally, if the client app enables exporters, OpenTelemetry libraries 1.4.0 and above depend on DiagnosticSource 7.0.0+, so they'll have to use one of the workarounds anyway.

[bgavrilMS]

Have you thought about merging both PRs? So that it fixes the assembly load and fallbacks when Az Functions moves from 6 to 8 (?). Alternatively, this PR is enough and when Az Functions updates, the upgrade will break some folks. This should be a strong signal that they need to figure out a better solution. Thoughts?

[neha-bhargava]

Were you able to test this with the exporter manually?

[pmaytak]

Have you thought about merging both PRs? So that it fixes the assembly load and fallbacks when Az Functions moves from 6 to 8 (?). Alternatively, this PR is enough and when Az Functions updates, the upgrade will break some folks. This should be a strong signal that they need to figure out a better solution. Thoughts?

Yea, I'll merge the PRs.

You mean when Azure Functions update their runtime to v8? I tested with a v5 library and everything works. So if they upgrade to v9 and we use v6/7, it's okay.

Were you able to test this with the exporter manually?

Yes, with the dev app. Workarounds still needed for in-process Function, but works otherwise.

[neha-bhargava]

I did a quick test with MISE exporter too and logs look fine. Thanks!