Docker Registries

A registry is a storage and distribution point for Docker images. Docker Hub is the default registry.

Registry Types

1. Docker Hub

# Log in
docker login

# Push an image
docker push username/myapp:latest

# Pull an image
docker pull nginx:latest

2. Private Registry

# Run a private registry
docker run -d -p 5000:5000 --name registry registry:2

# Tag the image
docker tag myapp:latest localhost:5000/myapp:latest

# Push to the registry
docker push localhost:5000/myapp:latest

3. Cloud Registry

# AWS ECR
aws ecr get-login-password --region us-east-1 | \
  docker login --username AWS --password-stdin 123456789.dkr.ecr.us-east-1.amazonaws.com

# Google Container Registry
gcloud auth configure-docker

# Azure Container Registry
az acr login --name myregistry

Use Case: Application Registry

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

# Tag the image for the myapp registry
docker tag myapp-api:1.0 localhost:5000/myapp-api:1.0

# Push to the myapp registry
docker push localhost:5000/myapp-api:1.0

# Pull from the myapp registry
docker pull localhost:5000/myapp-api:1.0

Registry Configuration

# docker-compose.yml
version: '3.8'

services:
  registry:
    image: registry:2
    ports:
      - "5000:5000"
    environment:
      REGISTRY_STORAGE_DELETE_ENABLED: "true"
    volumes:
      - registry-data:/var/lib/registry

  registry-ui:
    image: joxit/docker-registry-ui
    ports:
      - "8080:80"
    environment:
      REGISTRY_TITLE: "MyApp Registry"
      REGISTRY_URL: http://registry:5000
    depends_on:
      - registry

volumes:
  registry-data:

Everyday Use Case

Case: A DevOps team needs to manage internal images.

# Push a new image
docker build -t localhost:5000/myapp-app:2.0 .
docker push localhost:5000/myapp-app:2.0

# View all images in the registry
curl -s http://localhost:5000/v2/_catalog

# Delete an old image
curl -X DELETE http://localhost:5000/v2/myapp-app/manifests/<digest>

Best Practices

1. Use clear tags: app:v1.0 instead of app:latest
2. Scan for vulnerabilities: Before pushing to the registry
3. Back up the registry: Regular data backups
4. Use authentication: For controlled access
5. Monitor storage: Watch storage usage

Use Case: CI/CD Pipeline

# .github/workflows/docker.yml
jobs:
  build-and-push:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3

      - name: Login to Docker Hub
        uses: docker/login-action@v2
        with:
          username: ${{ secrets.DOCKER_USERNAME }}
          password: ${{ secrets.DOCKER_TOKEN }}

      - name: Build and push
        uses: docker/build-push-action@v4
        with:
          push: true
          tags: username/myapp-app:${{ github.sha }}

Troubleshooting

Registry cannot be accessed

# Check the registry status
docker ps | grep registry

# Check the registry logs
docker logs myapp-registry

# Check the port
curl http://localhost:5000/v2/

Push fails

# Check authentication
docker login localhost:5000

# Check the image tag
docker images | grep myapp

# Push with verbose output
docker push localhost:5000/myapp-app:1.0 2>&1

Conclusion

A Docker registry enables controlled image distribution. For applications, use a private registry to manage internal images securely.