managing-container-registries

What this skill does

# Managing Container Registries

## Overview

Manage container registries across Docker Hub, AWS ECR, GCP Artifact Registry, Azure ACR, and self-hosted registries (Harbor, Nexus). Automate image tagging, lifecycle policies, cross-region replication, vulnerability scanning integration, and access control for container image storage and distribution.

## Prerequisites

- Docker CLI installed and authenticated to the target registry
- Cloud provider CLI (`aws`, `gcloud`, `az`) for managed registries
- Registry credentials configured (`docker login` or credential helpers)
- Understanding of image naming conventions (registry/namespace/image:tag)
- IAM permissions for registry operations (push, pull, delete, admin)

## Instructions

1. Identify the target registry type: ECR, Artifact Registry, ACR, Docker Hub, or self-hosted
2. Configure authentication: set up credential helpers for automated access (`docker-credential-ecr-login`, `gcloud auth configure-docker`)
3. Define image naming and tagging strategy: use semantic versioning for releases, git SHA for CI builds, `latest` only for development
4. Create repository/namespace structure organized by team, application, or environment
5. Configure lifecycle policies to auto-delete untagged images and images older than retention threshold (e.g., keep last 10 tagged images, delete untagged after 7 days)
6. Set up vulnerability scanning: enable automatic scanning on push (ECR scan-on-push, GCP Container Analysis)
7. Configure cross-region replication for disaster recovery and latency reduction
8. Implement access control: read-only for CI pull, push access for CI build agents, admin for operators
9. Generate Terraform/IaC for registry infrastructure and policies

## Output

- Terraform/CloudFormation for registry creation with lifecycle and replication policies
- Docker credential helper configuration scripts
- CI/CD pipeline steps for building, tagging, and pushing images
- Lifecycle policy JSON (ECR) or cleanup scripts (Docker Hub, Harbor)
- RBAC configurations for registry access control

## Error Handling

| Error | Cause | Solution |
|-------|-------|---------|
| `denied: requested access to the resource is denied` | Missing push/pull permissions or expired token | Re-authenticate with `docker login` or refresh credential helper; verify IAM policies |
| `manifest unknown: manifest unknown` | Image tag does not exist in the registry | Verify image name and tag; check if lifecycle policy deleted the image |
| `no space left on device` during push | Registry storage quota exceeded | Increase quota, run lifecycle cleanup, or delete unused images |
| `unauthorized: authentication required` | Credential helper not configured or token expired | Set up credential helper (`aws ecr get-login-password`, `gcloud auth configure-docker`) |
| `toomanyrequests: rate limit exceeded` | Docker Hub pull rate limit hit | Use authenticated pulls, mirror images to private registry, or upgrade Docker Hub plan |

## Examples

- "Set up an AWS ECR repository with scan-on-push enabled, lifecycle policy to keep last 20 tagged images, and cross-region replication to us-west-2."
- "Configure GCP Artifact Registry with Docker credential helper and a cleanup policy for images not pulled in 90 days."
- "Create a CI pipeline step that builds a Docker image, tags it with the git SHA and `latest`, pushes to ECR, and fails if Critical vulnerabilities are found."

## Resources

- AWS ECR: https://docs.aws.amazon.com/AmazonECR/latest/userguide/
- GCP Artifact Registry: https://cloud.google.com/artifact-registry/docs
- Azure ACR: https://learn.microsoft.com/en-us/azure/container-registry/
- Harbor registry: https://goharbor.io/docs/
- Docker Hub: https://docs.docker.com/docker-hub/