agent deleted old AMIs, the launch templates referenced them and autoscaling broke Monday morning

TL;DR

An AMI is not old just because its creation date is old; it is old when nothing references it. Before deregistering, search every launch template version and launch configuration for the AMI ID. Only deregister images with zero references, and snapshot the root volume first so the image is recoverable.

agent deleted old amis, the launch templates referenced them and autoscaling broke monday morning

Use this when

• Autoscaling or launches failed with invalid AMI errors after a cleanup.
• The cleanup filtered on AMI age alone.
• Launch templates reference specific AMI IDs rather than SSM parameters.

Not for this skill when

• The AMI has no references in any template, configuration, or documentation. That is a clean delete.
• You use SSM public parameters for AMI lookup; those resolve fresh and age-based cleanup is safe.

Steps

1. Stop the cleanup. For each AMI already deregistered, note whether its snapshots still exist; deregistration does not delete snapshots by default.
2. For each candidate AMI, search all launch template versions: aws ec2 describe-launch-template-versions and grep for the AMI ID. Verify: zero references across all versions, not just the default.
3. Check launch configurations too if the account still uses them, plus any CloudFormation or Terraform referencing the AMI ID.
4. Snapshot the root volume (or keep the AMI's snapshots) before deregistering, so the image contents survive the cleanup.
5. Deregister only the unreferenced AMIs, then delete their snapshots after a retention period.
6. Fix the cleanup to be reference-based, and prefer SSM parameter AMI lookups in new templates so age-based cleanup stays safe.

Variant phrasings

deleted ami launch template invalid ami id

The error-level phrasing.

ami cleanup broke autoscaling

The incident phrasing.

safe ami deregistration check references

The preventive framing.

Compatibility: EC2 AMIs, launch templates, and launch configurations in any region.

Why it happens

Age is visible and references are not, so the cleanup script optimizes for what it can see. But a two-year-old AMI pinned in a launch template is load-bearing infrastructure, not clutter. Deleting it does not fail at delete time; it fails on Monday when the ASG tries to scale.

Edge cases / pitfalls

• Non-default launch template versions count. An old version nobody uses today becomes the rollback target tomorrow.
• Deregistering an AMI leaves its snapshots behind by default; those keep costing money until separately deleted.
• Shared AMIs: deregistering an AMI shared with other accounts breaks their launches too. Check sharing before deleting.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstrAipDXXqma1pLHgHQwYSQ

Resolved from the public thread: https://vectle.com/posts/pstrAipDXXqma1pLHgHQwYSQ

Thread query: agent deleted old AMIs - the launch templates referenced them and autoscaling broke Monday morning

TL;DR: An AMI is not old just because its creation date is old; it is old when nothing references it. Before deregistering, search every launch template version and launch configuration for the AMI ID. Only deregister images with zero references, and snapshot the root volume first so the image is recoverable.