WARNING!
Though most Ubuntu 9.04 Jaunty systems can upgrade to 9.10 Karmic in place, this is not possible on EC2 and should not be attempted. If you do try this, your system will become unusable on reboot and there will be no recovery and no access to any of the data on the boot disk or ephemeral storage.
Here’s why:
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Ubuntu 9.10 Karmic has a version of udev which requires a newer kernel than you would be running for Ubuntu 9.04 Jaunty (especially on EC2).
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You cannot upgrade the kernel used by a running instance on Amazon EC2 (not even rebooting).
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When an EC2 instance cannot boot (as in the case of the udev/kernel mismatch) your only option is to terminate it, losing the local storage.
How To Upgrade
In order to upgrade to Karmic you will need to start a new EC2 instance running a fresh copy of the appropriate Karmic AMI. I post the latest AMI ids for Karmic in the second table on https://alestic.com/.
Keep your old instance(s) running while you configure and test the new Karmic instances. EC2 makes it easy to have multiple sets of servers running in parallel instead of upgrading in place. When you are confident your new servers are functioning properly, you can discard the old ones.
The Ubuntu 9.10 Karmic AMIs released by Canonical have a number of differences from the community Ubuntu AMIs which have been published on https://alestic.com.
One of the biggest differences is that you will ssh to ubuntu@ instead of to root@ on your instance. You can then sudo to perform commands as the root user. Back in April I wrote a guide about Using sudo, ssh, rsync on the Official Ubuntu Images for EC2.
The Ubuntu server team has put a lot of work into making Ubuntu 9.10 Karmic function beautifully on Amazon EC2 and it’s been a pleasure to have a small part in the process. I’m already using the Karmic AMIs on EC2 for one of my production processes. Please give these AMIs a spin and give feedback.