Docker for Web Developers: Practical Containerization

Docker packages your application with its dependencies into a container that runs identically on any machine. Development, CI/CD, and production environments are identical, eliminating environment-related bugs.

Dockerfile basics: start FROM a base image (node:20-alpine for Node.js apps), COPY your code, RUN install commands, and define the CMD to start your application. Each instruction creates a layer.

Multi-stage builds reduce image size: use a build stage to compile/bundle your application, then copy only the output to a minimal runtime image. A Next.js image drops from 1GB+ to under 200MB.

Docker Compose for development: define your entire development stack (application, database, Redis, mailhog) in a docker-compose.yml. One command starts everything. New team members are productive in minutes.

Volume mounts for development: mount your source code as a volume so changes are reflected immediately without rebuilding the container. Hot reload works through volume mounts.

Environment variables: use .env files for configuration. Docker Compose reads .env automatically. Never bake secrets into Docker images. Pass secrets at runtime through environment variables.

Networking: Docker creates isolated networks for your containers. Services reference each other by container name (database, redis) instead of localhost. This mirrors production networking.

Image optimization: use .dockerignore to exclude node_modules, .git, and test files from the build context. Smaller contexts mean faster builds. Order Dockerfile instructions for optimal layer caching.

Production considerations: use non-root users in containers, implement health checks, set resource limits (memory, CPU), and scan images for vulnerabilities. Security is your responsibility.

Container orchestration: for production, use managed services (AWS ECS, Google Cloud Run, Railway) or Kubernetes for complex deployments. Most web applications do not need Kubernetes; managed services are simpler.