I’ve been hosting this server on an EC2 instance since New Year. Over the long weekend I decided to upgrade it to Ubuntu 10.04. When all the upgrade is done and the instance is restarted, I find myself locked out of the server – can’t ssh, can’t even ping. The instance actually fails to boot up (I found out about that by attaching the root volume to another instance and examining the logs). So it’s clearly a mismatching kernel issue – the instance still boots with the 9.10 stock kernel, which wouldn’t work when the rest of the system has been upgraded to 10.04.
I fixed the problem by following Eric Hammond’s article on how to Move a Running EBS Boot Instance to New Hardware on Amazon EC2. His original article was for scenarios where the instances become inaccessible due to power failures, but the methodology worked out in my case just fine.