Road Map for Docker Learning

Level 1: Containerization Fundamentals

1. Container vs VM

   • Definitions, isolation model, performance trade-offs

   • Linux namespaces & cgroups (basic idea)

2. Docker Architecture

   • Docker Daemon, CLI, Registry, Client-Server model

   • How images, containers, volumes, networks fit together

3. Core Commands

   • docker run, docker ps, docker stop, docker rm, docker rmi

   • Inspecting: docker logs, docker exec, docker inspect

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Level 2: Building & Packaging Images

1. Dockerfile Basics

   • FROM, RUN, COPY / ADD, ENTRYPOINT vs CMD, WORKDIR, ENV

   • Layering & caching: how build speed & image size are affected

2. Image Management

   • Tagging (my-app:1.0, latest), pushing & pulling from Docker Hub

   • docker build --no-cache, multi-stage builds (slim production images)

3. Best Practices

   • Minimizing layers & attack surface (e.g. use Alpine or distroless)

   • Pinning base-image versions, cleaning up temp files in same layer

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Level 3: Multi-Container Apps & Networking

1. Docker Compose

   • docker-compose.yml format: services, volumes, networks, depends_on

   • One-command workflows: docker-compose up / down / logs

2. Container Networking

   • Bridge, host, overlay networks

   • Port mapping (-p), linking vs user-defined networks

3. Data Persistence

   • Volumes vs bind-mounts vs tmpfs

   • Named volumes, backup/restoration strategies

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Level 4: Advanced Usage & Ecosystem

1. Registry & CI/CD Integration

   • Private registries (Docker Hub Organizations, AWS ECR, GCR)

   • Automated builds via GitHub Actions / Jenkins pipelines

2. Security & Hardening

   • Image scanning (Trivy, Snyk), least-privilege containers (--user)

   • Seccomp, AppArmor, user namespaces

3. Performance & Troubleshooting

   • Diagnosing slow builds, bloated images, container resource limits (--memory, --cpus)

   • Common gotchas: DNS issues, log verbosity, zombie processes

4. Orchestration Primer (interview talking-points)

   • Docker Swarm basics: services, stacks, overlay networking

   • When to move on to Kubernetes

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How to Use This Roadmap

• Hands-On: Build small sample apps (e.g. Spring Boot “Hello World”), containerize, link with Redis/MySQL via Compose.

• Explain & Diagram: Draw Docker’s architecture; talk through each layer in your Dockerfile.

• Mock Questions:

  • “What happens if you docker run --rm and the container crashes?”

  • “How does Docker cache layers, and how can you bust the cache selectively?”

  • “Compare bind mounts vs volumes. When would you use each?”

By following these levels—mastering commands and concepts first, then composing and securing multi-container systems, and finally understanding where Docker fits into CI/CD and orchestration—you’ll be ready to tackle both practical and whiteboard-style Docker questions in your interviews. Good luck!