When you login to GKE-OP nodes and try to run sudo command you will get the following warning:

sudo: unable to resolve host [nodename]

Your command will still execute but will show this warning. It is related to Ubuntu OS settings. To resolve it add the following line into the /etc/hosts file on the node:

127.0.0.1 [node-name]

Hope this will be solved soon as Google has already identified this issue. I guess they will add the record in the provisioning process for the nodes.