[TIL] Docker –dns may not behave like you expect

I always thought the --dns option in docker run or docker start etc. always set the DNS servers to what you specify there. It does, but there is a caveat. If you are using a custom network (e.g. a macvlan network like I tend to do) then this option is ignored when you attach the VM to that network. In such cases the DNS server within the VM is set to which is Docker’s embedded DNS that forwards requests to the external servers on the host. Bit me in the a$$ yesterday and thanks to this gitHub issue I am now the wiser.