Amazon ECR Container Image Management - Lifecycle Policies and Image Scanning
Learn how to automatically clean up old images with private repository lifecycle policies and detect vulnerabilities with image scanning.
ECR Basics and Repository Management
ECR is a managed registry for Docker container images and OCI artifacts, supporting layers up to 42 GB per image. It provides both private repositories and public repositories (ECR Public). Private repositories use IAM policies for access control, allowing configurations where only specific IAM roles can push and pull images. Images are encrypted at rest with AES-256, and KMS customer managed keys are also available. Enabling image tag immutability prevents overwriting an image with the same tag, ensuring deployment reproducibility.
Lifecycle Policies and Cost Management
Lifecycle policies are rules that automatically clean up images within a repository. You can define rules for tagged image retention count (e.g., keep the latest 10), untagged image retention period (e.g., delete after 7 days), and rules based on specific tag prefixes. In environments where CI/CD pipelines frequently push images, storage costs grow indefinitely without lifecycle policies. A recommended approach is to retain 30 generations of production images (prod-*) while keeping only 5 generations of development images (dev-*).
Image Scanning and Replication
Basic scanning detects OS package vulnerabilities using the Clair engine at push time. Enhanced scanning integrates with Inspector to detect vulnerabilities in programming language packages (npm, pip, Maven) in addition to OS packages. Enhanced scanning runs continuously, and existing images are re-scanned when new CVEs are published. Cross-region replication automatically copies images to specified regions, reducing image pull times for multi-region ECS/EKS deployments. Cross-account replication is also available, enabling architectures where images are distributed from a central repository to workload accounts. To broaden your knowledge of container technologies, specialized books on Amazon can also be helpful.
Summary
ECR is a managed registry that handles the entire container image lifecycle. Lifecycle policies automatically optimize storage costs, and image scanning continuously detects vulnerabilities. Cross-region replication and cross-account sharing streamline container image distribution across multi-region, multi-account environments.