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Docker Roadmap(2026 Edition)

Phase 0: Foundations

Prerequisites (Before Starting)

Essential knowledge required before learning Docker

What You MUST Already Know

  1. 1. Linux basics → Files, permissions, and process management
  2. 2. Networking basics → Ports, DNS, localhost, and TCP protocols
  3. 3. Git fundamentals → Clone, commit, and push operations
  4. 4. Backend stack → Node.js, Python, Java, or Go experience
  5. 5. Why: Docker does not replace understanding OS and networking fundamentals
Phase 0
Phase 1
Phase 1: Docker Basics

Week 1

Understanding Docker fundamentals and core concepts

What Docker Actually Is

  1. 1. Containers vs VMs → Process isolation, not OS virtualization
  2. 2. Images → Immutable templates for containers
  3. 3. Containers → Running processes from images
  4. 4. Docker Engine → Core runtime and daemon
  5. 5. Docker CLI → Command-line interface tools
  6. 6. Docker Desktop → GUI application for Windows and Mac
  7. 7. Outcome: Explain Docker in 2 minutes without buzzwords

Install & Verify

  1. 1. Docker Desktop → Installation for Windows and Mac
  2. 2. Docker Engine → Installation for Linux systems
  3. 3. docker version → Verify installation and version
  4. 4. docker info → Display system-wide information
  5. 5. docker run hello-world → Test basic functionality
  6. 6. Why: Everything depends on proper installation

Core Commands (Non-Negotiable)

  1. 1. docker pull → Download images from registries
  2. 2. docker images → List all local images
  3. 3. docker run → Create and start containers
  4. 4. docker ps → List running containers
  5. 5. docker ps -a → List all containers including stopped
  6. 6. docker stop → Stop running containers
  7. 7. docker rm → Remove containers
  8. 8. docker rmi → Remove images
  9. 9. docker logs → View container logs
  10. 10. docker exec -it → Execute commands in running containers
  11. 11. Why: Drill these until muscle memory

Run Real Containers

  1. 1. Run nginx → docker run -d -p 8080:80 nginx
  2. 2. Run redis → docker run -d redis
  3. 3. Run postgres → docker run -d -e POSTGRES_PASSWORD=pass postgres
  4. 4. Understand ports → Port mapping between host and container
  5. 5. Detached mode → Running containers in background
  6. 6. Environment variables → Passing configuration to containers
  7. 7. Outcome: Understand ports, detached mode, and env vars
Phase 1
Phase 2
Phase 2: Dockerfile Mastery

Week 2

Building custom images and optimization techniques

Dockerfile Basics

  1. 1. FROM → Specify base image for build
  2. 2. RUN → Execute commands during build
  3. 3. COPY vs ADD → Use COPY for files (ADD has extra features)
  4. 4. WORKDIR → Set working directory in container
  5. 5. EXPOSE → Document ports the container listens on
  6. 6. CMD vs ENTRYPOINT → Default command vs fixed executable
  7. 7. Why: This is where beginners break production

Build & Run Your Own Image

  1. 1. docker build -t myapp . → Build image with tag
  2. 2. docker run -p 3000:3000 myapp → Run custom image
  3. 3. Understanding build context → Files sent to Docker daemon
  4. 4. Tagging conventions → Naming and versioning images
  5. 5. Why: If you can't do this, you're not using Docker

Image Optimization (CRITICAL)

  1. 1. Layer caching → Understanding Docker layer reuse
  2. 2. .dockerignore → Exclude files from build context
  3. 3. Alpine vs Debian → Choosing minimal base images
  4. 4. Multi-stage builds → Separate build and runtime environments
  5. 5. Example: FROM node:20 AS build → Build stage separation
  6. 6. COPY --from=build → Copy artifacts between stages
  7. 7. Why: This alone separates juniors from pros

Debugging Containers

  1. 1. docker logs → Inspect container output
  2. 2. docker exec → Interactive debugging inside containers
  3. 3. Container exits immediately → Troubleshooting startup issues
  4. 4. Common mistakes → Wrong CMD, missing env vars, port mismatches
  5. 5. Exit codes → Understanding container failure reasons
Phase 2
Phase 3
Phase 3: Data, Volumes & Networking

Week 3

Managing persistent data and container communication

Volumes (State is King)

  1. 1. Named volumes → docker volume create data
  2. 2. Bind mounts → Mount host directories into containers
  3. 3. Volume usage → docker run -v data:/var/lib/mysql mysql
  4. 4. Volume management → List, inspect, and remove volumes
  5. 5. When NOT to use volumes → Temporary data and logs
  6. 6. Data persistence → Understanding container ephemeral nature

Docker Networking

  1. 1. Bridge network → Default network driver for containers
  2. 2. Container-to-container communication → DNS-based discovery
  3. 3. docker network create app-net → Create custom networks
  4. 4. docker run --network app-net → Connect to networks
  5. 5. Network isolation → Security through network separation
  6. 6. Why: Stop using localhost incorrectly

Environment Management

  1. 1. .env files → Storing configuration separately
  2. 2. Secrets → Don't hardcode sensitive data
  3. 3. docker run --env-file .env → Load environment files
  4. 4. ENV instruction → Setting defaults in Dockerfile
  5. 5. Security considerations → Keeping secrets out of images
Phase 3
Phase 4
Phase 4: Docker Compose

Week 4

Multi-container application orchestration

Docker Compose Basics

  1. 1. services → Define application components
  2. 2. ports → Port mapping configuration
  3. 3. volumes → Persistent data management
  4. 4. networks → Custom network configuration
  5. 5. depends_on → Service startup dependencies
  6. 6. Why: Compose is mandatory in industry

Multi-Service Architecture

  1. 1. Backend + DB + Redis + Nginx → Full stack setup
  2. 2. Reverse proxy → Nginx as API gateway
  3. 3. Healthchecks → Container health monitoring
  4. 4. Service discovery → DNS-based service location
  5. 5. Scaling services → Running multiple instances

Dev vs Prod Compose

  1. 1. docker-compose.override.yml → Development overrides
  2. 2. Different environments → Staging and production configs
  3. 3. Debug vs optimized builds → Build optimization per environment
  4. 4. Environment-specific variables → Configuration management
  5. 5. Compose profiles → Conditional service activation
Phase 4
Phase 5
Phase 5: Security & Best Practices

Week 5

Container security and production-ready configurations

Container Security

  1. 1. Non-root users → Run containers with limited privileges
  2. 2. Minimal base images → Reduce attack surface
  3. 3. Scan images → docker scan myimage for vulnerabilities
  4. 4. Security updates → Keep base images updated
  5. 5. Read-only filesystems → Prevent runtime modifications
  6. 6. Why: Most devs are dangerously bad here

Secrets Management

  1. 1. .env is NOT secure → Understanding environment limitations
  2. 2. Docker secrets → Swarm and Compose secret management
  3. 3. External secret managers → Vault, AWS Secrets Manager
  4. 4. Runtime secrets → Injecting secrets at container start
  5. 5. Never commit secrets → .gitignore and security practices

Resource Limits

  1. 1. CPU limits → cpus: '0.5' configuration
  2. 2. Memory limits → memory: 512M constraints
  3. 3. Resource reservations → Guaranteed resources
  4. 4. Why containers can kill hosts → Understanding resource exhaustion
  5. 5. Monitoring resources → docker stats command
Phase 5
Phase 6
Phase 6: Registries & CI/CD

Week 6

Image distribution and automated workflows

Image Registries

  1. 1. Docker Hub → Public registry for images
  2. 2. GitHub Container Registry → GHCR for private images
  3. 3. Private registries → Self-hosted solutions
  4. 4. docker tag app user/app → Tagging for registries
  5. 5. docker push user/app → Publishing images
  6. 6. Registry authentication → Login and access tokens

Docker in CI/CD

  1. 1. Build in GitHub Actions → Automated image building
  2. 2. Cache layers → Speed up builds with layer caching
  3. 3. Push on merge → Automatic deployment workflows
  4. 4. Multi-platform builds → ARM and x86 support
  5. 5. Why: You should never build manually in production
Phase 6
Phase 7
Phase 7: Docker in Real Systems

Week 7-8

Production deployment and integration patterns

Docker + Nginx

  1. 1. Reverse proxy → Load balancing and routing
  2. 2. SSL with Certbot → HTTPS certificate automation
  3. 3. Multiple apps on one server → Virtual host configuration
  4. 4. Static file serving → Optimized content delivery
  5. 5. Nginx as API gateway → Request routing and authentication

Docker + Databases

  1. 1. Backup strategies → Volume snapshots and exports
  2. 2. Migrations → Database schema management
  3. 3. Production data safety → Preventing data loss
  4. 4. Replication → Database high availability
  5. 5. Performance tuning → Database optimization in containers

Docker vs Kubernetes

  1. 1. Why Docker alone fails at scale → Orchestration limitations
  2. 2. Where K8s starts → Multi-host container management
  3. 3. Service discovery → Advanced networking requirements
  4. 4. Auto-scaling → Dynamic resource allocation
  5. 5. Why: Learn Docker before Kubernetes, no shortcuts
Phase 7
Phase 8
Phase 8: Advanced & Industry Level

Optional but Powerful

Advanced features and enterprise patterns

Advanced Topics

  1. 1. BuildKit → Next-generation build system
  2. 2. Docker context → Managing multiple Docker hosts
  3. 3. Rootless Docker → Running Docker without root privileges
  4. 4. Docker swarm → Legacy orchestration knowledge
  5. 5. Custom network drivers → Advanced networking plugins

Observability

  1. 1. Logs aggregation → Centralized logging with ELK or Loki
  2. 2. Prometheus exporters → Metrics collection and monitoring
  3. 3. Health probes → Liveness and readiness checks
  4. 4. Distributed tracing → Request flow visualization
  5. 5. APM integration → Application performance monitoring

Anti-Patterns (Memorize)

  1. 1. One container = many processes ❌ → Violates single responsibility
  2. 2. Storing secrets in images ❌ → Security vulnerability
  3. 3. Huge images ❌ → Slow builds and deployments
  4. 4. latest tag in prod ❌ → Non-deterministic deployments
  5. 5. Running as root ❌ → Security risk
  6. 6. No healthchecks ❌ → Poor failure detection
Phase 8
Phase 9
Phase 9: Final Industry Checklist

Job-Ready Skills

Essential capabilities for professional Docker usage

Core Competencies

  1. 1. ✅ Containerize a backend → Full application dockerization
  2. 2. ✅ Use multi-stage builds → Optimized production images
  3. 3. ✅ Use Docker Compose for full stack → Multi-service applications
  4. 4. ✅ Persist DB data safely → Volume management and backups
  5. 5. ✅ Push images to registry → CI/CD integration
  6. 6. ✅ Deploy on VPS with Nginx → Production deployment
  7. 7. ✅ Debug failing containers fast → Troubleshooting skills

🚀 Congratulations! You're Docker Industry Ready!

You've completed the Docker Roadmap and are now ready to build scalable web apps.