I have been connecting via ssh to my GCP Compute Engine VM all day at work without issues.
I then used my work VPN this evening, and also ssh'd to my VM. Once I lost connect to the VM (computer went to sleep), I could not ssh back onto the VM, and the serial port logs show: "invalid ssh key entry - expired key"
So, it appears that GCP Compute Engine does not properly handle the usage of VPNs.
...and now I cannot connect to my VM.
Solved! Go to Solution.
The issue was due to the disk space completely filling up.
A more useful message than "invalid ssh key entry - expired key" would be quite helpful.
For instance, the Compute Engine console could provide information on disk space usage and warn when empty disk space is running out.