kubectl output verbosity and debugging

--v=0 Generally useful for this to always be visible to a cluster operator.
--v=1 A reasonable default log level if you don’t want verbosity.
--v=2 Useful steady state information about the service and important log messages that may correlate to significant changes in the system. This is the recommended default log level for most systems.
--v=3 Extended information about changes.
--v=4 Debug level verbosity.
--v=6 Display requested resources.
--v=7 Display HTTP request headers.
--v=8 Display HTTP request contents.
--v=9 Display HTTP request contents without truncation of contents.

reference:
https://kubernetes.io/docs/reference/kubectl/cheatsheet/#kubectl-output-verbosity-and-debugging
https://github.com/kubernetes/community/blob/master/contributors/devel/sig-instrumentation/logging.md