AWS EC2 (AMI)

EBS-backed

• Boot time < 1 minute
  • Only needed parts must be downloaded from S3 (EBS Snapshot)
  • Performance slower initially as blocks are being downloaded (but not later when you stop-start)
• Max 16TiB
• Instance Type, kernel, RAM disk, user data can be changed when stopped (unlike Instance Store)
• AMI creation - single command
• Deletion on termination
  
  • root volume deleted, non-root volumes retained
  • this policy can be changed
• Ephemeral Storage
  • By default not available at boot time
  • Device block mapping must be specified explicitely
    • at boot time
    • in AMI configuration
• Typically used

Instance Store-backed

• Uses Instance Store volumes
• Not dependant on EBS service
  • Can attach EBS as additional disks
  • Fewer failure modes
• Boot time < 5 minutes
  • All the parts must be downloaded from S3
• Max 10GiB
• Instance attributes are fixed (cannot stop instance)
  • Canot change Instance Type, kernel Ram Disk, etc.
• AMI bundling - multiple tools need to be used
• No cost for root EBS volume
  • Potentially higher cost for AMI storage as the whole image is stored (not differential as in case of EBS Snapshot)
• Windows Instance Store AMI cannot be converted to EBS-backed AMI
• Rarely used

Copying

• Can be copied cross-region (asynchronously)
• Can encrypt the target copy
• Use case
  • DR

Sharing

• Private
  
  • Can be shared with specific AWS account (sharee)
    • "Create Volume" permission allows direct access to snapshots
    • Sharee can see it in his "Private AMIs" view
• Public
• Encrypted AMIs cannot be shared
  • Encrypted snapshots CAN be shared

References

• http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ComponentsAMIs.html#storage-for-the-root-device