I have a server running the recent Ubuntu AMIs from Canonical. The size of the EBS boot volume is 8GB. I know that I can resize EBS volumes by taking a snapshot, creating a new volume and expanding the partition on it. How can I increase the size of the volume while the machine is running? If this is not possible, what is the preferred method for increasing the boot volume size with minimal downtime?
Unfortunately it is not possible to increase the size of an Amazon EBS root device storage volume while the Amazon EC2 instance is running - Eric Hammond has written a detailed (I'm inclined to say the 'canonical' ;) article about Resizing the Root Disk on a Running EBS Boot EC2 Instance:
As long as you are ok with a little down time on the EC2 instance (few minutes), it is possible to change out the root EBS volume with a larger copy, without needing to start a new instance.
If you properly prepare the steps he describes (I highly recommend to test them with a throw away EC2 instance first to get acquainted with the procedure), you should be able to finish the process with a few minutes downtime only indeed.
Good luck!