UPDATE-3: As of 2009-06-16 02:35a, Canonical has restored the Ubuntu mirror for EC2 in the US region. It looks like everything is operating normally now.
UPDATE-2: Canonical has restored the Ubuntu mirror for EC2 in the EU region.
UPDATE-1: The DNS names for the Canonical Ubuntu mirrors on EC2 have been temporarily switched to point to the Ubuntu mirrors outside of EC2. This is a great idea that gets things working again until the EC2 mirrors can be brought back up. If you really want to use mirrors inside EC2 for performance or (minor) cost considerations, you could still switch to the RightScale mirrors.
As I write this, the Ubuntu archive mirrors on EC2 run by Canonical are currently unavailable in both the US and European regions. If you are running the Ubuntu images for EC2 published by Canonical, this prevents you from being able to apt-get update or apt-get upgrade
The Canonical IS team is currently on the job investigating and correcting the issue, but if you need a quick fix in the mean time, you can run the following command on the instance to switch to a Canonical Ubuntu mirror outside of EC2 (standard EC2 network charges apply):
oldarchive='(us|eu)\.ec2\.archive\.ubuntu\.com'
newarchive='$1.archive.ubuntu.com'
sudo perl -pi.orig -e "s/$oldarchive/$newarchive/" /etc/apt/sources.list
This command saves a copy of the original file in /etc/apt/sources.list.orig so that you can copy it back when the outage is over.
Alternatively, you could switch to the Ubuntu mirror in EC2 run by RightScale:
oldarchive='[.\w]+\.archive\.ubuntu\.com'
newarchive='ec2-us-east-mirror.rightscale.com'
sudo perl -pi.orig -e "s/$oldarchive/$newarchive/" /etc/apt/sources.list
Note that RightScale does not mirror the source packages, so you might want to comment out the deb-src lines:
sudo perl -pi -e 's/^(deb-src)/#$1/' /etc/apt/sources.list
The Ubuntu images for EC2 that I publish on https://alestic.com use the RightScale Ubuntu mirrors by default and are not affected by the current outage.