> I can't include Python and ilk as their purpose is completely different, although for things like backends both could be used.
Yet, many real world sysadmin programs formerly written in Python are now written in Go. Go's compilation to a single statically linked binary, and tool support for easy cross-compilation makes it popular for these usecases. And when many people say "Go is blazingly fast!" they compare it to Python.
> What else could we use to write Docker or Kubernetes
Borg, I think, was written in Java at Google.