ERROR: (gcloud.compute.ssh) [/usr/bin/ssh] exited with return code [255]

Solution 1:

gcloud denies an ssh connection if there was a change in the setup, e.g. after you changed your default zone or region, or you created another instance. Then, you must update the ssh keys in your metadata by

sudo gcloud compute config-ssh

If this complains about different entries in your config file where your ssh key entries are stored, ~/.ssh/config, delete this file and execute the above command again.

If you have installed gcloud without sudo, you can omit sudo.

Solution 2:

255 is the interactive ssh exit code for ssh failure - otherwise interactive ssh exits with the exit code of the last command executed in the ssh session.

The next time you get exit code 255 from ssh try running with --ssh-flag="-vvv" (more v's => more debugging output) and see if it helps track down connection problems.