binding port-forwards to a non-localhost DNS fails

[nicks]

Start tilt like

tilt up --host dev.localhost --port=10450

if you have port forwards, you'll get an error:

Reconnecting... Error port-forwarding api (5734 -> 5000): error forwarding port: dev.localhost is not a valid IP

The error is coming from here:

https://kubernetes.io/docs/reference/generated/kubectl/kubectl-commands#port-forward

Only accepts IP addresses or localhost as a value. When localhost is supplied, kubectl will try to bind on both 127.0.0.1 and ::1 and will fail if neither of these addresses are available to bind.

I don't totally understand why this restriction exists, or even if this is a bug. It seems like it would be trivial to resolve the DNS to an IP, so I am probably missing something. Needs further investigation.

[nicksieger]

It looks like the original proposal (kubernetes/kubernetes#43962) and implementation (kubernetes/kubernetes#46517) simply decided not to implement the extra DNS lookup. Looking into how we can convert the --host argument into an ip address at the point where we create the port forwards.