Docker for Developers: Containerizing Your Applications

Docker for Developers: Containerizing Your Applications

Introduction

[Explain why containerization improves parity, onboarding speed, and CI/CD reliability.]

Prerequisites

• Docker Desktop installed
• Basic knowledge of CLI
• Sample Node.js or .NET project

Core Concepts

Step-by-Step Guide

Step 1: Create a Minimal Dockerfile

FROM node:20-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .
CMD ["node", "src/index.js"]

Step 2: Build & Run Locally

docker build -t myapp:dev .
docker run --rm -p 3000:3000 myapp:dev

Step 3: Add Multi-Stage Build (Optimization)

FROM node:20-alpine AS build
WORKDIR /src
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

FROM node:20-alpine AS runtime
WORKDIR /app
COPY --from=build /src/dist ./dist
CMD ["node", "dist/index.js"]

Step 4: Debugging Containers

[Describe VS Code devcontainers, attach debugger, logs]

Step 5: Compose Multi-Service Dev Env

version: "3.9"
services:
  api:
    build: .
    ports: ["5000:5000"]
  redis:
    image: redis:7-alpine
    ports: ["6379:6379"]

Best Practices

• Use smallest base image (alpine/distroless where possible)
• Pin versions explicitly
• Keep layers ordered to leverage caching

Common Issues & Troubleshooting

Issue: Large image size
Solution: Multi-stage builds + .dockerignore

Issue: Container restarts
Solution: Check healthcheck & app logs

Key Takeaways

• Containerization accelerates environment parity.
• Multi-stage builds reduce size & deployment time.
• Compose simplifies local multi-service orchestration.

Next Steps

• Push image to GitHub Container Registry
• Integrate image scan in CI pipeline

Additional Resources

• Docker Docs
• VS Code Dev Containers
• GitHub Container Registry

What was your biggest win after adopting Docker?