Zipkin exporter does not serialize event attributes into a JSON string (the spec says it MUST)

[sno544]

Question about providing Event details (message.id and message.type) in events emited for every gRPC request and response.

In Golang service that uses gRPC I was able to obtain traces like on the picture below. Events emited by every request and response produce some additional information - message.id, message.type and so on. Traces are exported to Jaeger.

Unfortunately for Java springboot services that uses gRPC communication as well I didn't manage to do the same.
So my question is - is it possible to configure Java agent to produce the same set of information? And if s how to do it?

Regards

[mateuszrzeszutek]

Hey @sno544 ,
What span exporters are you using in each of these cases?

[sno544]

Hi @mateuszrzeszutek , thanks for replying.
In both cases it's Zipkin exporter.
Forgot to mention - on the Java side I'm using autoconfiguration - apart from specifying zipkin as exporter and zipkin endpoint (config provided by env variables) all settings and instrumentation are default.

[mateuszrzeszutek]

That's interesting, looks like Go's Zipkin exporter is behaving in a bit different way compared to the Java one -- it serializes span event attributes to JSON string: https://github.com/open-telemetry/opentelemetry-go/blob/042d938989bfe4960c96328328f1f324bc72bdf3/exporters/zipkin/model.go#L147

It looks like the Java Zipkin exporter does not conform to the OTel spec when converting span events to annotations: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk_exporters/zipkin.md#events

I'd say that this looks like a bug in the Zipkin exporter implementation. Nonetheless, I would also suggest using the OTLP exporter instead, now that Jaeger supports receiving OTLP data. The Zipkin data format is somewhat limited, and it does not really fit greatly with OTel, and the events/annotations conversion is a prime example of that: instead of structured data you'll just get a JSON string with all event attributes.

[mateuszrzeszutek]

Transferring to the SDK repo cause that's where the Zipkin exporter code lives.