How to collect profiling info from Haskell service running in Kubernetes?

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I have a microservice written in Haskell, the compiler is 8.8.3. I built it with --profile option and ran it with +RTS -p. It is running about 30 minutes, there is <my-service>.prof file but it is empty (literally 0 bytes). Previously I did it on my local machine and I stop the service with CTRL-C and after the exit it produced <my-service>.prof file which was not empty.

So, I have 2 questions:

  1. How to collect profiling information when a Haskell microservice runs under Kubernetes in the most correct way (to be able to read this .prof file)?
  2. How to pass run time parameter to Haskell run-time where to save this .prof file (maybe some workaround if no such an option), for 8.8.3 - because I have feeling that the file may be big and I can hit disk space problem. Also I don't know how to flush/read/get this file while microservice is running. I suppose if I will be able to pass full path for this .prof file then I can save it somewhere else on some permanent volume, to "kill" the service with INT signal for example, and to get this .prof file from the volume.

What is the usual/convenient way to get this .prof file when the service runs in Kubernetes?

PS. I saw some relevant options in the documentation for newest versions, but I am with 8.8.3

kubernetes profiling haskell
1 Answers

I think the only way to do live profiling with GHC is to use the eventlog. You can insert Debug.Trace.traceEvent into your code at the functions that you want to measure and then compile with -eventlog and run with +RTS -l -ol <output-file-name> -RTS. You can use ghc-events-analyze to analyze and visualize the produced eventlog.

The official eventlog documentation for GHC 8.8.3 is here.

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