Add SpanProcessor for OpenTelemetry

[solnic]

To make this work you need to add opentelemetry deps:

      {:opentelemetry, "~> 1.3"},
      {:opentelemetry_api, "~> 1.2"},
      {:opentelemetry_exporter, "~> 1.6"},
      {:opentelemetry_phoenix, "~> 2.0"},
      {:opentelemetry_ecto, "~> 1.2"},
      {:opentelemetry_bandit, "~> 0.2"}

Then configure our span processor:

config :opentelemetry, span_processor: {Sentry.OpenTelemetry.SpanProcessor, []}

Things should start looking more or less like this:

[solnic]

1) test loads in_app_module_allow_list (Public.Sentry.ConfigTest)
Error:      apps/public/test/public_test.exs:4
     ** (RuntimeError) the Sentry configuration seems to be not available (while trying to fetch :in_app_module_allow_list). This is likely because the :sentry application has not been started yet. Make sure that you start the :sentry application before using any of its functions.

     code: assert Sentry.Config.in_app_module_allow_list() |> Enum.sort() ==
     stacktrace:
       (sentry 10.8.1) lib/sentry/config.ex:698: Sentry.Config.in_app_module_allow_list/0
       test/public_test.exs:5: (test)


Finished in 0.00 seconds (0.00s async, 0.00s sync)
1 test, 1 failure
==> admin
Running ExUnit with seed: 25[95](https://github.com/getsentry/sentry-elixir/actions/runs/13856201920/job/38773483717?pr=875#step:10:96)1, max_cases: 8



  1) test loads in_app_module_allow_list (Admin.Sentry.ConfigTest)
Error:      apps/admin/test/admin_test.exs:4
     ** (RuntimeError) the Sentry configuration seems to be not available (while trying to fetch :in_app_module_allow_list). This is likely because the :sentry application has not been started yet. Make sure that you start the :sentry application before using any of its functions.

     code: assert Sentry.Config.in_app_module_allow_list() |> Enum.sort() ==
     stacktrace:
       (sentry 10.8.1) lib/sentry/config.ex:6[98](https://github.com/getsentry/sentry-elixir/actions/runs/13856201920/job/38773483717?pr=875#step:10:99): Sentry.Config.in_app_module_allow_list/0
       test/admin_test.exs:5: (test)

@whatyouhide ☝🏻 I'm having trouble figuring out these failures. Could you tell me how I could debug what exactly causes the :sentry app startup failure? We start it manually in the umbrella test helpers and for whatever reason it started failing when opentelemetry is included.

[whatyouhide]

Adding just the OTel deps without any other changes leads to the same issue?

[sl0thentr0py]

please write some minimal description in the PR about

• what functionality this adds
• instructions to add this to a Phoenix app with opentelemetry instrumentation and test it out

[solnic]

Adding just the OTel deps without any other changes leads to the same issue?

@whatyouhide @sl0thentr0py I narrowed it down to opentelemetry dep. When it's included, the app doesn't start in umbrella integration test. We need to make otel deps optional anyway, so it's time to address this. How do we want to approach it though? Should I create sentry-opentelemetry package in this repo?

[solnic]

@whatyouhide for the time being I addressed it by using optional deps for otel packages via 6fdf121 but then one of the tests in event_test.exs started to fail so I fixed it via d04c5d3 even though I don't understand what's going on there 🙃

[whatyouhide]

@solnic is this ready for review? It's still a draft

[solnic]

@solnic is this ready for review? It's still a draft

Not yet. I got it working but phoenix + bandit spans are not processed in a way that would make sense for Sentry for some reason. I've been investigating how to fix. It seems like phoenix spans are not coming in as children of bandit spans so there's a disconnect here. I'll figure it out 🙂

[sl0thentr0py]

We need to make otel deps optional anyway, so it's time to address this.

If we're just shipping a SpanProcessor first, having them as peer dependencies is more than fine. We just document well how to get otel up and running in parallel to sentry and hook them up properly.

We will revisit packaging later once we have a proper working prototype.

[solnic]

@sl0thentr0py @whatyouhide this is now open for reviews. I got it deployed to production already and it's working well (see screenshots in the description).

[sl0thentr0py]

okay I'm taking a preliminary look now

one thing we definitely need is that instead of the boolean Config.tracing we need

• a traces_sample_rate
• also ideally, a traces_sampler callback

without these, it is very hard for people to control quota spend so this is a hard requirement

[sl0thentr0py]

some suggestions, looks very good otherwise!

[sl0thentr0py]

The way you've implemented it, we can do nothing in on_start since the on_end logic is sufficient to build the span tree and transaction.

This will also simplify your SpanStorage.update_span where you can remove the unnecessary deletes.
(This is also how we've done it in the new python and JS span processors.)

[solnic]

@sl0thentr0py I'll dig into this more but when I make on_start a no-op the tests are no longer passing 🙃

[whatyouhide]

Looking like a good start but still a bunch of work left to do. Let me know if any of the comments are not clear!

[whatyouhide]

@solnic I’m assuming you're still working on this so re-request my review if this gets ready again.

[solnic]

@solnic I’m assuming you're still working on this so re-request my review if this gets ready again.

@whatyouhide yes, wrapping it up today, still a couple of things to address 🙃

[solnic]

• also ideally, a traces_sampler callback

without these, it is very hard for people to control quota spend so this is a hard requirement

@sl0thentr0py I'll add traces_sampler config in a separate PR

[solnic]

@whatyouhide @sl0thentr0py ready for another round of reviews 🤞🏻

[whatyouhide]

I'll review tomorrow.

[whatyouhide]

Can you elaborate on why we need a Sentry-specific sampler?

[solnic]

@whatyouhide in order to provide a standard interface for traces_sampler option we need a custom abstraction for this

[whatyouhide]

I don't think this conversation is resolved?