Trace only some endpoints in .Net Core

[rvignesh89]

Is your feature request related to a problem? Please describe.
Yes. I would like to install the .Net Core APM agent on a Web API to trace a particular endpoint which is slow. However when I install Elastic.Apm.AspNetCore it starts listening to all requests through the ApmMiddleware. Since my API has very high request rates, I'd most likely have to set a TransactionSampleRate config to avoid any performance hits. However, I'm afraid by setting this I'll miss samples from the single endpoint for which I want to monitor all the calls.
The reason I can't sample calls on that particular endpoint is because the response time of that endpoint varies wildly based on the parameters it receives which is exactly what I'd like to observe.

Describe the solution you'd like
I'd like to have a way to enable tracing only on particular controllers instead of listening in on all using the middleware appraoch.

Describe alternatives you've considered
A couple of alternative approaches that I can think off-

1. I realize that I can achieve what I want by initiating the elastic apm agent as done in the (ApmMiddlewareExtensions) but it's not easy for me to just instantiate the agent without turning on the middleware.
2. If the lib can provide a way to instantiate the Agent without adding the middleware I could easily start a transaction myself wherever I need to trace. Actually I'm able to do that right now, but the agent tries to write the logs to localhost:8200 which I'm guessing the default endpoint used when not properly configured.

Additional context

[gregkalapos]

Thanks for opening this.

Yeah, this totally makes sense.

Other agents offer a config for this: ELASTIC_APM_IGNORE_URLS. E.g. here is the doc for it in Java.

I think best would be to align with those. I feel that would also solve your problem - do you also think so?

Regarding:

Actually I'm able to do that right now, but the agent tries to write the logs to localhost:8200 which I'm guessing the default endpoint used when not properly configured.

Yes, you can change it - easiest is to set the ELASTIC_APM_SERVER_URLS environment variable to your real apm server url - docs.

[rvignesh89]

Yes, I think it's what I was looking for. If I can submit PR would it be possible to get this merged?

I'll also try out setting ELASTIC_APM_SERVER_URLS without calling UseElasticApm and see if that works for me.

[gregkalapos]

If I can submit PR would it be possible to get this merged?

Yes, of course - all PRs get reviewed and once they are ok and approved we are happy to merge. We have a CONTRIBUTING.md to help (make sure to sign the CLA :) ).

[gregkalapos]

@rvignesh89 there were some differences on this across agents. We had 1 issue to harmonize this across agents.

I just opened #688 which is based on elastic/apm#144 - that's usually our process to be aligned across agents - first we have an APM issue in https://github.com/elastic/apm/ and then each agent creates a corresponding issue.

In case you open a PR, please make sure you follow the new issue.

I'd close this one if you are ok with it and keep #688.

[rvignesh89]

I'm fine with closing this. Will follow up with #688. Thanks!