Lesson 1: The Warehouse (Docker Registry)

You've built an image on your laptop. How do you get it to the production server? You push it to a registry — a warehouse for Docker images.

What is a Registry?

A Docker registry is a service that stores and distributes Docker images. Think of it like GitHub, but for containers instead of code.

Popular Registries

| Registry | URL | Type | |----------|-----|------| | Docker Hub | hub.docker.com | Public/Private | | GitHub Container Registry | ghcr.io | Public/Private | | AWS ECR | aws.amazon.com/ecr | Private | | Google Artifact Registry | cloud.google.com | Private | | Azure Container Registry | azure.microsoft.com | Private |

The Push/Pull Workflow

Developer Laptop          Registry          Production Server
┌──────────┐   push →   ┌──────────┐   ← pull   ┌──────────┐
│  Build   │ ─────────→ │  Store   │ ←───────── │  Deploy  │
│  Image   │            │  Image   │            │  Image   │
└──────────┘            └──────────┘            └──────────┘

Logging In

docker login                          # Docker Hub
docker login ghcr.io                  # GitHub
docker login 123456789.dkr.ecr.us-east-1.amazonaws.com  # AWS ECR

Tagging Images

Before pushing, you must tag your image with the registry path:

# Format: registry/repository:tag
docker tag my-app:v1 cloudcorp/my-app:v1
docker tag my-app:v1 ghcr.io/cloudcorp/my-app:v1

Pushing Images

docker push cloudcorp/my-app:v1

Docker uploads each layer individually. Layers that already exist in the registry are skipped (deduplication).

Pulling Images

docker pull cloudcorp/my-app:v1
docker pull cloudcorp/my-app:latest

Searching Docker Hub

docker search nginx

NAME           DESCRIPTION                          STARS   OFFICIAL
nginx          Official Nginx image                 18000   [OK]
jwilder/nginx  Automated nginx reverse proxy        2100

Look for the OFFICIAL badge — these are maintained by the software authors.

Image Tagging Strategy

| Tag | Purpose | Example | |-----|---------|---------| | latest | Most recent build | my-app:latest | | Semantic version | Specific release | my-app:2.1.0 | | Git SHA | Exact commit | my-app:a1b2c3d | | Date | Build timestamp | my-app:2025-05-19 | | Environment | Target deployment | my-app:staging |

Best practice: Use specific versions in production, never latest.

Mission Objective

Work with the registry:

1. Search: Run docker search nginx to browse available images.
2. Tag: Tag your image with docker tag my-app:v1 cloudcorp/my-app:v1.
3. Inspect layers: Run docker history nginx to see how an image was built.

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