AMIs and Storage: EBS-Backed vs Instance Store
~12 min read
What an AMI actually contains, and the difference between network-attached EBS storage and physically-local instance store.
An AMI (Amazon Machine Image) is a template containing the operating system, any pre-installed software/configuration, and launch permissions, used to boot new EC2 instances. AWS provides a library of maintained base AMIs (Amazon Linux, Ubuntu, Windows Server, etc.), the AWS Marketplace offers vendor-published AMIs (e.g. a pre-configured database appliance), and you can create your own custom AMI by configuring an instance exactly how you want it and then taking an image of it — a 'golden image' workflow used heavily in Auto Scaling so every new instance launches pre-configured and ready, with no boot-time setup script needed.
Most modern EC2 instances are EBS-backed: the root volume lives on EBS (Elastic Block Store), AWS's network-attached block storage service, which persists independently of the instance's lifecycle — you can stop an EBS-backed instance and its data survives, and you can even detach the volume and attach it to a different instance. A smaller set of instance types offer Instance Store volumes: physically local NVMe/SSD storage directly attached to the specific physical host the instance is running on, offering very high IOPS/throughput but with a critical caveat — data on instance store is lost if the instance stops, terminates, or the underlying hardware fails, making it suitable only for temporary/cache data, not anything you need to persist.
In the AWS Console
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EC2 → Instances → select a configured instance → Actions → Image and templates → Create image
Name the image; AWS snapshots the instance's EBS volumes and registers a new AMI you can launch future instances from.
The instance is briefly rebooted by default during this process (unless you check 'No reboot') to ensure filesystem consistency in the snapshot.
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Key points
- •AMI = template (OS + software + config) an instance boots from; can be AWS-provided, Marketplace, or your own custom 'golden image'
- •EBS-backed root volumes persist independently of the instance and survive a stop/start cycle
- •Instance Store volumes are physically local, very fast, but lost on stop/terminate/hardware failure
- •Custom AMIs are the standard way to make Auto Scaling launches fully pre-configured, avoiding boot-time setup scripts