Do Google Compute instances have a stable public DNS name?

Question

This is a question in two parts:

• Do GCE instances have a stable public DNS name? The default DNS name for instance with public IP a.b.c.d seems to be d.c.b.a.bc.googleusercontent.com

• If yes, what's the best way to obtain this information? Here's the hack I've been using thus far:

  EXTERNAL_IP=$(curl -s http://bot.whatismyipaddress.com/)
  EXTERNAL_DNS=$(dig +short -x ${EXTERNAL_IP})
  

Answer 1

GCE instances don't currently have a public DNS name for their external IP address. But there is now a gcloud compute config-ssh (docs) command that's a pretty good substitute.

This will insert Host blocks into your ~/.ssh/config file that contain the IP address and configuration for the host key.

Although this only helps with SSH (and SSH-based applications like Mosh and git+ssh), it does have a few advantages over DNS:

• There is no caching/propagation delay as you might have with DNS

• It pre-populates the right host key, and the host key is checked the right way even if the ephemeral IP address changes.

Example:

$ gcloud compute config-ssh
...
$ ssh myhost.us-west1-b.surly-koala-232

Answer 2

reverse lookup is okay to do, for IP address you would probably prefer using gcutil https://developers.google.com/compute/docs/gcutil/tips

EXTERNAL_IP=$(gcutil getinstance --format=csv --zone=[your_zone] [your_instance] | grep external-ip | cut -d "," -f 2)