Custom TracesSamplerCallback cannot access Spring request attributes when using OTEL

[lcian]

Integration

sentry-opentelemetry-agentless-spring

Java Version

17

Version

8.1.0

Steps to Reproduce

1. Create a project with spring-boot-starter-web (customer is using v2.7.11, but this is not relevant), sentry-spring-boot-starter and sentry-opentelemetry-agentless-spring
2. Follow the docs to set up a custom TracesSamplerCallback that returns different sample rates based on the request path
3. Start application and send HTTP request

Reported by pretchu in this Discord thread

Expected Result

Custom sample rate is returned based on request path, as correctly happens when using the SDK in non-OTEL mode.

Actual Result

context.getCustomSamplingContext() is always null, hence the request path cannot be inspected to make a sampling decision.

[adinauer]

As a workaround in theory this SO post should work for OTel as well.

For the future we probably want to send OpenTelemetry span attributes into the sampling context.
We should check whether sampling is going to be implemented differently with the new Performance API.

[adinauer]

AFAIR python recently address this, we should check how they implemented sending of OTel span attributes into the sampler callback.