Intelligently create a scratch EBS of the correct size
Rather than guessing what the the root volume size should be, the EC2 instance could:
- Check the total size of the EFS volume, CW metric? parse
dfoutput? - Create an EBS volume slightly larger than that
- Attach it to itself
- Format the volume with a filesystem
- Mount it
- Run the backup
- Delete the volume
- Terminate itself