Is there a list of trace context propagators that the Java client supports?

[joe-elliott]

I'm looking for documentation that lists the various ways that the Java client can propagate trace context (HTTP, GRPC, ??).

In particular I'm wondering if it automatically propagates through Kafka.

[mateuszrzeszutek]

We don't have that documented because we (usually) implement context propagation in all libraries that we instrument - you can assume that all HTTP/PRC/messaging libs listed here propagate context properly.

Kafka, however, is a know source of context propagation problems 😅 Because of its poll-based consumer API it's pretty hard to correctly wrap a CONSUMER span around message processing, and depending on the way you're using it you might or might not get your context propagated correctly. If you're able to, please try the agent out - and if you find any context propagation issues with Kafka, don't hesitate to create a bug and attach an example of how you use the Kafka consumer.

[joe-elliott]

So context is propagated through Kafka, but depending on the way it's being used it's possible that it won't propagate? Is there any more details about the right or wrong way to use it? or should i just give it a shot?

[mateuszrzeszutek]

KafkaConsumer#poll() returns a ConsumerRecords, which is essentially an Iterable (or it returns an Iterable with its records() method). As long as you iterate over it "normally" it'll work - we start the span on next() and end it on hasNext(), so if you remember to call hasNext() at the end (e.g. hasNext()->next()->hasNext()->...->hasNext()) all the spans will get started and ended properly.

[mateuszrzeszutek]

If you make a copy of the list, use .get() or something other than iteration you'll run into problems with that though.

[joe-elliott]

Thank you for the help!