Apply a lifecycle policy to AWS ECR repositories created automatically by pull-through cache rules using a repository creation template

Steps

1. Create a repository creation template using the AWS CLI: aws ecr create-pull-through-cache-rule (or use aws ecr put-repository-creation-template) specifying the prefix that matches pull-through cache repository names and including a lifecyclePolicy JSON document in the template
2. In the lifecycle policy document, define a rule with the tagStatus: any condition and set maxImageAge to the desired number of days to expire images not pulled recently
3. If pull-through cache repositories already exist without a lifecycle policy, apply policies retroactively using aws ecr put-lifecycle-policy --repository-name <REPO> --lifecycle-policy-text file://policy.json
4. Verify that the template was applied by describing the template with aws ecr describe-pull-through-cache-rules and confirming the repositoryCreationTemplate field contains the policy
5. Monitor storage reclamation by checking ECR Storage Bytes metrics in CloudWatch after the lifecycle policy evaluation runs (typically within 24 hours of policy application)