container-registries – DevOps & Infrastructure skill for AI agents

Container Registries

Store, manage, and distribute container images across cloud and self-hosted registries.

When to Use This Skill

Use this skill when:

• Pushing and pulling container images
• Configuring registry authentication
• Setting up image retention policies
• Managing private container registries
• Implementing image scanning and security

Prerequisites

Confirm account/region/repository and image digest before pushing, publishing, granting cross-account access or enabling deletion policies. Preview cleanup candidates and preserve deployment/rollback digests. ACR retention and geo-replication require a supported SKU (the Standard setup above does not enable every later feature). Google cleanup policy files require the current CLI schema; validate the illustrative object before use. The Harbor archive/flags and Docker Content Trust are historical examples, not universal current signing instructions. TLS alone does not authorize registry clients: configure authentication/access controls before network exposure, and do not run both same-name registry examples simultaneously.

• Docker or Podman installed
• Cloud CLI tools (AWS CLI, az, gcloud) for respective registries
• Appropriate IAM permissions

Docker Hub

Authentication

# Login
docker login

# Login with token
echo "$DOCKER_TOKEN" | docker login -u username --password-stdin

Push/Pull Images

# Tag image
docker tag myapp:latest username/myapp:latest

# Push
docker push username/myapp:latest

# Pull
docker pull username/myapp:latest

Automated Builds

Configure in Docker Hub UI:

1. Connect GitHub/Bitbucket repository

2. Set build rules (branch → tag mapping)

3. Configure build context and Dockerfile path

Amazon ECR

Setup

# Create repository
aws ecr create-repository \
  --repository-name myapp \
  --image-scanning-configuration scanOnPush=true \
  --encryption-configuration encryptionType=AES256

# Get registry URI
REGISTRY=$(aws ecr describe-repositories \
  --repository-names myapp \
  --query 'repositories[0].repositoryUri' \
  --output text | cut -d'/' -f1)

Authentication

# Login (Docker)
aws ecr get-login-password --region us-east-1 | \
  docker login --username AWS --password-stdin $REGISTRY

# Login with credential helper
# Add to ~/.docker/config.json:
{
  "credHelpers": {
    "123456789.dkr.ecr.us-east-1.amazonaws.com": "ecr-login"
  }
}

Push/Pull

# Tag and push
docker tag myapp:latest $REGISTRY/myapp:latest
docker push $REGISTRY/myapp:latest

# Pull
docker pull $REGISTRY/myapp:latest

Lifecycle Policy

# Create lifecycle policy
aws ecr put-lifecycle-policy \
  --repository-name myapp \
  --lifecycle-policy-text '{
    "rules": [
      {
        "rulePriority": 1,
        "description": "Keep last 10 images",
        "selection": {
          "tagStatus": "any",
          "countType": "imageCountMoreThan",
          "countNumber": 10
        },
        "action": {
          "type": "expire"
        }
      }
    ]
  }'

Repository Policy

# Allow cross-account access
aws ecr set-repository-policy \
  --repository-name myapp \
  --policy-text '{
    "Version": "2012-10-17",
    "Statement": [
      {
        "Sid": "CrossAccountPull",
        "Effect": "Allow",
        "Principal": {
          "AWS": "arn:aws:iam::OTHER_ACCOUNT:root"
        },
        "Action": [
          "ecr:GetDownloadUrlForLayer",
          "ecr:BatchGetImage"
        ]
      }
    ]
  }'

Azure Container Registry (ACR)

Setup

# Create registry
az acr create \
  --resource-group mygroup \
  --name myregistry \
  --sku Standard \
  --admin-enabled false

# Get login server
az acr show --name myregistry --query loginServer -o tsv

Authentication

# Login with Azure CLI
az acr login --name myregistry

# Login with service principal
printf '%s' "$SP_PASSWORD" | docker login myregistry.azurecr.io \
  -u "$SP_APP_ID" --password-stdin

# Get access token
az acr login --name myregistry --expose-token

Push/Pull

# Tag and push
docker tag myapp:latest myregistry.azurecr.io/myapp:latest
docker push myregistry.azurecr.io/myapp:latest

# ACR Build (build in cloud)
az acr build \
  --registry myregistry \
  --image myapp:latest \
  --file Dockerfile .

Retention Policy

# Enable retention policy
az acr config retention update \
  --registry myregistry \
  --status enabled \
  --days 30 \
  --type UntaggedManifests

Geo-Replication

# Enable replication
az acr replication create \
  --registry myregistry \
  --location westeurope

# List replications
az acr replication list --registry myregistry

Google Container Registry (GCR) / Artifact Registry

Setup (Artifact Registry)

# Create repository
gcloud artifacts repositories create myrepo \
  --repository-format=docker \
  --location=us-central1 \
  --description="Docker repository"

Authentication

# Configure Docker auth
gcloud auth configure-docker us-central1-docker.pkg.dev

# Or use credential helper
gcloud auth print-access-token | \
  docker login -u oauth2accesstoken --password-stdin \
  https://us-central1-docker.pkg.dev

Push/Pull

# Tag for Artifact Registry
docker tag myapp:latest \
  us-central1-docker.pkg.dev/PROJECT_ID/myrepo/myapp:latest

# Push
docker push us-central1-docker.pkg.dev/PROJECT_ID/myrepo/myapp:latest

# Pull
docker pull us-central1-docker.pkg.dev/PROJECT_ID/myrepo/myapp:latest

Cleanup Policy

# Create cleanup policy
gcloud artifacts repositories set-cleanup-policies myrepo \
  --location=us-central1 \
  --policy=policy.json

# policy.json
{
  "name": "delete-old",
  "action": {"type": "Delete"},
  "condition": {
    "olderThan": "30d",
    "tagState": "untagged"
  }
}

GitHub Container Registry (GHCR)

Authentication

# Login with PAT
echo "$GITHUB_TOKEN" | docker login ghcr.io -u USERNAME --password-stdin

Push/Pull

# Tag
docker tag myapp:latest ghcr.io/OWNER/myapp:latest

# Push
docker push ghcr.io/OWNER/myapp:latest

# Pull
docker pull ghcr.io/OWNER/myapp:latest

Visibility Settings

Configure in GitHub:

1. Go to package settings

2. Change visibility (public/private)

3. Manage access for teams/users

Self-Hosted Registry

Deploy with Docker

# Run registry
docker run -d -p 127.0.0.1:5000:5000 \
  --name registry \
  -v registry-data:/var/lib/registry \
  registry:2

# Configure TLS
docker run -d -p 443:5000 \
  --name registry \
  -v /certs:/certs \
  -v registry-data:/var/lib/registry \
  -e REGISTRY_HTTP_TLS_CERTIFICATE=/certs/domain.crt \
  -e REGISTRY_HTTP_TLS_KEY=/certs/domain.key \
  registry:2

Harbor Registry

# Download Harbor
wget https://github.com/goharbor/harbor/releases/download/v2.9.0/harbor-online-installer-v2.9.0.tgz
tar xzvf harbor-online-installer-v2.9.0.tgz

# Configure harbor.yml
# Set hostname, https certificate, admin password

# Install
./install.sh --with-trivy --with-chartmuseum

Image Security

Vulnerability Scanning

# ECR - Enable scan on push
aws ecr put-image-scanning-configuration \
  --repository-name myapp \
  --image-scanning-configuration scanOnPush=true

# Get scan results
aws ecr describe-image-scan-findings \
  --repository-name myapp \
  --image-id imageTag=latest

# ACR: enable/configure Microsoft Defender for Containers/registries through
# the supported subscription workflow, then inspect findings; there is no
# generic `az acr run-scan` command.

Image Signing

# Enable content trust
export DOCKER_CONTENT_TRUST=1

# Sign image on push
docker push myregistry/myapp:latest

# Verify signature
docker trust inspect myregistry/myapp:latest

Common Issues

Issue: Authentication Expired

Problem: Push/pull fails with auth error

Solution: Re-run login command, check credential helper

Issue: Image Not Found

Problem: Pull fails with manifest unknown

Solution: Verify tag exists, check registry URL

Issue: Push Permission Denied

Problem: Cannot push to repository

Solution: Check IAM permissions, verify repository exists

Issue: Rate Limiting (Docker Hub)

Problem: Too many requests error

Solution: Authenticate for higher limits, use pull-through cache

Best Practices

• Enable vulnerability scanning on all repositories
• Implement lifecycle policies to manage storage costs
• Use immutable tags for production images
• Configure cross-region replication for availability
• Use service accounts/principals for CI/CD authentication
• Enable audit logging for compliance
• Implement image signing for supply chain security
• Use pull-through cache to avoid rate limits

Related Skills

• docker-management (docker-management) - Building images
• container-scanning (container-scanning) - Security scanning
• aws-iam (aws-iam) - AWS permissions

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