Docker Registries

A Docker registry is a storage and distribution system for Docker images. When you run docker pull nginx, Docker downloads the image from a registry. When you build an image on your machine and want to deploy it to a server, you push it to a registry so the server can pull it.

Docker Hub

Docker Hub is the default public registry at https://hub.docker.com. It hosts official images for popular software (nginx, postgres, redis, node, python, and thousands more) as well as community and personal images.

Image names on Docker Hub follow the pattern username/repository:tag. Official images (maintained by Docker and upstream vendors) use just repository:tag — for example, nginx:latest or postgres:16.

# Log in to Docker Hub
docker login

# Pull an official image
docker pull postgres:16

# Pull a user image
docker pull myusername/my-app:1.0

# Tag a local image for Docker Hub
docker tag my-app:latest myusername/my-app:1.0

# Push to Docker Hub
docker push myusername/my-app:1.0

# Log out
docker logout

Image Naming and Tagging

Understanding image references is important when working with multiple registries:

• nginx — shorthand for docker.io/library/nginx:latest
• myuser/my-app — shorthand for docker.io/myuser/my-app:latest
• ghcr.io/myorg/my-app:v2.0 — fully qualified reference to GitHub Container Registry

# Tag for multiple registries
docker tag my-app:latest myuser/my-app:1.0
docker tag my-app:latest ghcr.io/myorg/my-app:1.0

# Push to both
docker push myuser/my-app:1.0
docker push ghcr.io/myorg/my-app:1.0

Private Registries

In production you often want a private registry so that your images are not publicly visible. Major cloud providers offer managed registries:

• Amazon ECR (Elastic Container Registry)
• Google Artifact Registry
• Azure Container Registry
• GitHub Container Registry (ghcr.io)

# Log in to Amazon ECR (requires AWS CLI configured)
aws ecr get-login-password --region us-east-1   | docker login --username AWS --password-stdin     123456789.dkr.ecr.us-east-1.amazonaws.com

# Tag and push to ECR
docker tag my-app:latest   123456789.dkr.ecr.us-east-1.amazonaws.com/my-app:latest
docker push   123456789.dkr.ecr.us-east-1.amazonaws.com/my-app:latest

Running a Local Registry

For development or air-gapped environments you can run Docker's open-source registry image:

# Start a local registry on port 5000
docker run -d -p 5000:5000 --name registry registry:2

# Tag and push to the local registry
docker tag my-app:latest localhost:5000/my-app:latest
docker push localhost:5000/my-app:latest

# Pull from the local registry
docker pull localhost:5000/my-app:latest

Semantic Versioning and Tagging Strategy

A good tagging strategy makes it easy to roll back and track what is deployed: