Previously we were reassigning os.Stderr to the panic.log file we create
when getting asked to run Containerd as a Windows service. The panic.log
file was used as a means to easily collect panic stacks as Windows
services don't have regular standard IO, and the usual recommendation
is to either write to the event log or just to a file in the case of
running as a service.
One place where this panic.log flow was biting us was with shim logging,
which is forwarded from the shim and copied to os.Stderr directly which was
causing shim logs to get forwarded to this panic.log file instead of just
panics. We expose an additional `--log-file` flag if you ask to run a
windows service which is the main way you'd get Containerd logs, and with
this change all of the shim logging which would today end up in panic.log
will now also go to this log file.
Signed-off-by: Daniel Canter <dcanter@microsoft.com>
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