Jaeger exporter no longer needed

[errordeveloper]

Jaeger already supports OTLP, so some of the code dedicated to handling Jaeger's own protocol can be remove in favour of OTLP.

[errordeveloper]

I think there are two feasible options:

• remove all of the code Jaeger-specific code, and log warning when user tries to configure any of Jaeger-specific environment variables (it would very odd if environmnet variable resulted in hard errors)
• just setup OTLP client against Jaeger endpoint user configures, warn that this is the case and user should migrate to OTLP

[errordeveloper]

Doing this would allow us to remove significant portion of the code in utils/tracing.

Thе code that can be removed includes imported internal conversion code from the SDK

https://github.com/moby/buildkit/blob/4451e1be0e6889ffc56225e54f7e26bd6fdada54/util/tracing/transform/span.go#L22

which originates from go.opentelemetry.io/otel/exporters/otlp/otlptrace/internal/tracetransform" , and it is only needed due to the use of otlptrace.Exporter interface instead of otlptrace.Client, as that's the inteface Jaeger exporter implements.

(I wish the code had a comment saying where it was imported from, I only found this by chance after digging for a few hours).

Furthermore, there is complex code to do with provider detection and registration etc

https://github.com/moby/buildkit/blob/4451e1be0e6889ffc56225e54f7e26bd6fdada54/util/tracing/detect/detect.go#L35

Instead of all this, it should be possible to just use a few of the OpenTelemetry SDK functions.

[tonistiigi]

transform.Spans is not used by Jaeger but by the client-side traces proxy.

[errordeveloper]

transform.Spans is not used by Jaeger but by the client-side traces proxy.

Could you please provide a link?

I didn't say it was used by utils/tracing/detect/jaeger, I was saying that it's needed because of reliance on otlptrace.Exporter interface that has ExportSpans(ctx, []sdktrace.ReadOnlySpan) error, rather then otlptrace.Client that has UploadTraces(context.Context, []*tracepb.ResourceSpans) error and does the transform before calling underlying ExportSpans. And my reading of the code is that ExportSpans is the common denominator due to Jaeger exporter, which only implements otlptrace.Exporter, so doesn't have UploadTraces and only has ExportSpans.