Docker Basics for Developers

Docker standardizes the runtime environment and makes packaging and deploying applications predictable. This guide covers practical Docker usage for development and the next steps for deploying containers to managed platforms.

1. Key concepts

• Image: a layered, read-only artifact built from a Dockerfile.
• Container: a running image with isolated namespaces.
• Registry: a place to store images (Docker Hub, Amazon ECR, Google Artifact Registry).

2. Writing a simple Dockerfile (Node.js example)

FROM node:18-alpine AS build
WORKDIR /app
COPY package*.json ./
RUN npm ci --production=false
COPY . ./
RUN npm run build
 
FROM node:18-alpine AS runtime
WORKDIR /app
COPY --from=build /app/dist ./dist
COPY package*.json ./
RUN npm ci --production
CMD ["node", "dist/index.js"]

Multi-stage builds separate the build toolchain from the runtime image to reduce final image size and attack surface.

3. Image size and optimization

• Choose minimal base images (Alpine, Distroless) when possible.
• Remove package manager caches and unnecessary dev files in the final stage.
• Use .dockerignore to exclude build artifacts and local files.

4. Docker Compose for local integration

Use docker-compose.yml to run multi-service stacks locally (app, database, cache). Keep production and dev compose files separate and avoid shipping secrets in compose files.

5. Development workflows

• Use bind mounts for live code reload in development.
• Use devcontainers (VS Code) for consistent developer environments.

6. Security and scanning

• Scan images for vulnerabilities (Trivy, Snyk) and keep base images patched.
• Run containers with non-root users where possible.

7. CI/CD and registries

• Build images in CI and push to a registry; tag images with CI build numbers and commit SHA.
• Use immutable tags and deploy by digest in production.

8. Running containers in the cloud

• For small teams, use managed services (Fargate, Cloud Run, App Service).
• For advanced orchestration, use Kubernetes (AKS/EKS/GKE).

Internal links

• Pillar: Practical Cloud Computing for Developers
• Related: Kubernetes for Application Developers
• Related: Getting Started with AWS for Developers
• Related: Getting Started with Azure for Developers

References

• Docker documentation: https://docs.docker.com/
• Trivy image scanner: https://github.com/aquasecurity/trivy