Add non-blocking send to kafka provider

[nemanjamikic]

Because zipkin is not critical component if kafka producer queue is full all messages should be logged and ignored. This is optional feature.

[coveralls]

Coverage decreased (-2.8%) to 72.599% when pulling a97fc6c on nemanjamikic:feature/non-blocking-send into c29478e on openzipkin:master.

[coveralls]

Coverage decreased (-14.8%) to 60.653% when pulling 6989a5b on nemanjamikic:feature/non-blocking-send into c29478e on openzipkin:master.

[jcchavezs]

Hi @nemanjamikic, thanks for the contribution and sorry for the delay in answering. I am curious about the options Config.Producer.Timeout from Sarama library. Will that do the trick instead? So as far as I see the main issue is that when kafka is not responding, the messages get stuck and the queue grows up because the buffered channel blocks. Would it be better if one decides the timeout so that the requests to kafka don't get stuck for 10s (default in Sarama).

What do you think?

cc @jeqo @basvanbeek @adriancole

[nemanjamikic]

Hi @jcchavezs , thank you for responding to issue.
We solved current issue with Config.Producer.Timeout set to 1s. However, i think that zipkin should not depend how client is configured because it can do harm if misconfigured on production server.

[jcchavezs]

Hi @nemanjamikic I have mixed feelings here. While I believe what you say it's true, I am ITOH not sure about the fact that one accept the Producer as part of the properties of the reporter (see https://github.com/openzipkin/zipkin-go/blob/master/reporter/kafka/kafka.go#L56) but don't fully respect the configurations on it.

Any input @adriancole @basvanbeek

[basvanbeek]

I don't see a technical problem to solve here only a documentation / expectation issue. I suggest we handle this by improving documentation and probably an example

[basvanbeek]

Instead of importing the concern of Sarama configuration into the Zipkin Go package I'd much rather see a fix of documentation as well as addition of proper usage of this reporter in an example.

[jcchavezs]

Closed in favour of #158. Still thanks a lot for the initiative @nemanjamikic!