I recently worked with a client where there were a number of Amazon EC2 AMIs where not all of the disk volumes were set to delete on termination. This caused quite a few snapshots to become orphaned when the associated AMI was deleted. This was discovered when there were hundreds of snapshots and no active snapshot plan.

To fix this issue, I wrote a script that will loop through all snapshots that have been created as part of a AMI and deleting them if that AMI no longer exists.

Note that this process should be used with a process to set all volumes to delete on termination to prevent future orphans.

This script requires the EC2 command line tools.

Note that you should be 100% comfortable with this script before running it as it will delete snapshots. On the other hand, they are only snapshots, it will not delete EC2 instances.

#!/bin/bash

images=$(ec2-describe-images  | awk '/IMAGE/ {print $2}')
invalid_count=0
valid_count=0

IFS='
'

for snapshot in $(ec2-describe-snapshots)
do
  snapshotid=$(echo ${snapshot} | sed -n 's/.*\(snap-[a-z0-9]\{4,8\}\).*/\1/p')
  amiid=$(echo ${snapshot} | sed -n 's/.*\(ami-[a-z0-9]\{4,8\}\).*/\1/p')

  if [ -z ${amiid} ]
  then
    # not related to AMI
    continue;
  fi  

  valid=$(echo ${images} | egrep -c ${amiid})
  if [ "${valid}" -gt 0 ] 
  then
    valid_count=$((valid_count+1))
  else
    echo "Deleting orphaned snapshot ${snapshotid} which belongs to non-existent AMI ${amiid}"
    invalid_count=$((invalid_count+1))
    ec2-delete-snapshot ${snapshotid}
  fi  

done

unset IFS

echo "Valid snapshots:  ${valid_count}"
echo "Invalid snapshots:  ${invalid_count}"

exit 0;

Let me know if you find any issues.

– josh