DNS For Instance with ephemeral external IP

[David Troyer]

I was curious if there is a way to specify an external facing hostname for a compute engine instance with an ephemeral IP address? This is an instance I only spin up on occasion, so I don't want to pay for a static IP.

I've tried ddclient, but it doesn't seem to have access to the external IP address, only the internal one. I've tried looking at routing but I don't think that's what I need.

Any thoughts?

David Troyer

[Kamran (Google Cloud Support)]

Hello David,

You can read the external IP address of your VM instance from metadata server. The metadata server is accessible by querying any of the following URLs:

• Full URL: http://metadata.google.internal/computeMetadata/v1/
• Shorthand URL: http://metadata/computeMetadata/v1/
• IP address: http://169.254.169.254/computeMetadata/v1/

To read the external IP address of the VM, run this curl command from inside of your instance:

curl http://metadata/computeMetadata/v1/instance/network-interfaces/0/access-configs/0/external-ip -H "Metadata-Flavor: Google"

Sincerely,

Kamran

[Bernhard Reinel]

(Just in case you are still interested, or someone else stumbles accross this topic.)

Example for ddclient config (/etc/ddclient.conf) on GCE:

protocol=dyndns2   #Set according to your provider

use=cmd, cmd='curl -s http://metadata/computeMetadata/v1/instance/network-interfaces/0/access-configs/0/external-ip -H "Metadata-Flavor: Google"'

ssl=yes   #Remove if you have problems using SSL (not supported with every provider)

server=<your-provider-url>

login=<your-login>

password=<your-password>

your.domain.com

Using cmd-mode to acquire ephemeral IP from metadata endpoint.

Don't forget to adapt config in /etc/default/ddclient to run ddclient as daemon.

Best,

Bernhard