I've run into a very strange issue where I don't seem to be getting any stdout/stderr output from a Haskell application when run via Kubernetes.
I'm using very basic putStrLn to write to stdout.
If I manually enter the container within the Kubernetes environment and run the application via the shell - I see the expected output.
What may be the cause of this issue/
It seems this is caused by the output buffering being set in "block" mode when being output to the kubernetes logging.
Fixed via setting the buffering to LineBuffering:
import System.IO
...
hSetBuffering stdout LineBuffering
hSetBuffering stderr LineBufferinghttp://hackage.haskell.org/package/base-4.12.0.0/docs/System-IO.html#t:BufferMode
The default buffering mode when a handle is opened is implementation-dependent and may depend on the file system object which is attached to that handle. For most implementations, physical files will normally be block-buffered and terminals will normally be line-buffered.
Thanks to Jesse Kempf from the fp slack for pointing me to this!