Learn Docker Roadmap

A practical roadmap to go from zero Docker knowledge to confidently containerizing apps, composing multi-service environments, and shipping images in CI/CD pipelines.

study, coding, productivity

by Morris

Container Concepts

Before touching the CLI, understand what containers are and why they exist. Most Docker confusion comes from skipping this.

• Understand the problem Docker solves
• Learn the difference between VMs and containers
• Understand the key terms: image, container, layer, registry, Dockerfile
• Understand why containers are ephemeral by default
• Read the official "Docker overview" documentation page

Docker Installation and CLI Basics

Install Docker and learn the essential commands to run and inspect containers.

• Install Docker Desktop (Mac/Windows) or Docker Engine (Linux)
• Run your first container with docker run
• Learn the essential container lifecycle commands
• Learn image management commands
• Inspect a running container's metadata and config

Working with Images

Images are the core unit of Docker. Understanding layers and tags is essential for efficient workflows.

• Understand image layers and why they matter for caching
• Understand image tags and the latest trap
• Pull images from Docker Hub and explore available tags
• Build an image and tag it
• Inspect image layers with docker history
• Push an image to Docker Hub

Writing Dockerfiles

The Dockerfile is the recipe for your image. Learning its instructions and best practices directly affects image size, build speed, and security.

• Learn the core Dockerfile instructions
• Understand CMD vs ENTRYPOINT
• Order Dockerfile instructions to maximize layer cache hits
• Create a .dockerignore file
• Build a multi-stage Dockerfile to produce a minimal production image
• Choose minimal base images: prefer alpine or distroless over full OS images

Container Management

Day-to-day commands for working with running containers.

• Map container ports to host ports
• Pass environment variables to containers
• Execute commands inside a running container
• Name containers for easier management
• Understand container restart policies

Volumes and Data Persistence

Containers are ephemeral - data written inside is lost on removal. Volumes solve this.

• Understand the two main persistence mechanisms: named volumes and bind mounts
• Know when to use each type
• Persist a PostgreSQL database with a named volume
• List, inspect, and remove volumes
• Use bind mounts for live code reloading during development

Networking Between Containers

Containers need to talk to each other. Docker networking makes this safe and straightforward.

• Understand the default bridge network and its limitations
• Create a custom bridge network for container name resolution
• Expose ports vs publish ports
• Connect a container to multiple networks
• Inspect network configuration with docker network inspect

Docker Compose

Compose lets you define and run multi-container apps with a single YAML file. It is the standard tool for local development environments.

• Write a docker-compose.yml for a simple web app with a database
• Learn the essential Compose commands
• Use an env file with Compose to avoid hardcoding secrets
• Understand depends_on and service health checks
• Use Compose profiles to separate dev-only services (e.g., a DB admin UI)
• Override compose config for different environments with compose.override.yml

Docker in CI/CD Pipelines

Using Docker in CI ensures your tests run in the same environment as production.

• Build and push a Docker image in a GitHub Actions workflow
• Use multi-stage builds to keep CI images small
• Cache Docker layers in CI to speed up builds
• Run tests inside a container in CI to match the production environment
• Tag images with the git commit SHA for full traceability

Security Best Practices

Default Docker configurations are convenient but not secure. These changes matter most.

• Never run containers as root
• Use minimal base images to reduce the attack surface
• Scan images for vulnerabilities with docker scout or trivy
• Never put secrets in Dockerfiles or image layers
• Set the filesystem to read-only where possible
• Use Docker Content Trust to verify image authenticity

Registry and Image Distribution

Publishing and consuming images from registries - the last step before deployment.

• Push an image to Docker Hub
• Use GitHub Container Registry (ghcr.io) for private images
• Design a tagging strategy for production deployments
• Pull and run an image from a private registry
• Set up automated image builds on push with GitHub Actions

Real-World Project

Containerize a complete multi-service application to apply everything from this roadmap.

• Choose a project: containerize an existing app or build a new one
• Write a production-grade Dockerfile with multi-stage build and non-root user
• Write a docker-compose.yml for the full local development environment
• Add a .dockerignore file and verify the image size is reasonable
• Set up a GitHub Actions workflow to build and push the image on each push to main
• Deploy the container to a cloud service (Fly.io, Railway, Render, or a VPS)
• Scan the final image for vulnerabilities and fix any critical findings