Borrowed this from a site I had to pull up via Google's cache with some additions.

I recently needed to convert an AWS instance-store AMI to an EBS backed AMI. Here’s the steps I took in order to fix that. It’s a ext3 file system in this example, but it should work fine with an ext4 as well.

  1. Launch your instance-store AMI

  2. Create a new EBS in the same availability zone

  3. Attach the EBS to the instance-store instance on /dev/sdh

  4. Create the file system
    If you're trying to decide which filesystem to use: Phoronix Comparison of FileSystems. tl;dr version:

    • NILFS2 has better random read performance
    • EXT3 has better multi threaded read performance
    • EXT4 has better overall performance.
mkfs.ext3 /dev/sdh  
  1. Mount the device
mkdir /mnt/ebs  
mount /dev/sdh /mnt/ebs  
  1. Shut down any running applications or databases that you have and
    rsync your system to the EBS volume
rsync -avHx / /mnt/ebs  
rsync -avHx /dev /mnt/ebs  
  1. Label the device
tune2fs -L '/' /dev/sdh  
  1. Sync and unmount the device
sync;sync;sync;sync && umount /mnt/ebs  
  1. In the AWS Console, make a snapshot of the EBS drive
  2. Make a note of the AKI and ARI of the currently running instance (skip this if none are set)
  3. When the snapshot is complete, right click on it and choose "Create Image from Snapshot"
  4. Use the wizard to set an name and description of your new AMI. Also choose the right AKI etc.
  5. You should now be able to start a new instance from the newly created AMI.