Docker Dev Setup

Docker Dev Setup

Create a production-grade Docker setup for any application: multi-stage Dockerfile, Compose for local development services, .dockerignore, and optional VS Code Dev Container.

When to Use

• Dockerizing an application for the first time
• Creating a multi-stage Dockerfile for smaller, secure images
• Setting up Docker Compose for local development (app + database + cache)
• Adding a .dockerignore to speed up builds and prevent secret leaks
• Optimizing an existing Docker image (size, build speed, security)
• Creating a Dev Container for VS Code / GitHub Codespaces
• Debugging Docker build failures or runtime issues

Tools Used

• Read — inspect existing project files (package.json, requirements.txt, go.mod, existing Dockerfiles)
• Write — create Dockerfile, compose.yaml, .dockerignore, devcontainer.json
• Edit — modify existing Docker configuration
• Bash — run docker build, docker compose, check image size
• Glob — find project entry points, existing Docker files
• Grep — detect frameworks, dependencies, existing Docker usage

Bundled Files

docker-dev-setup/
├── references/
│   ├── dockerfile-patterns.md    # Multi-stage builds, caching, security
│   ├── compose-patterns.md       # Services, health checks, volumes, networking
│   └── troubleshooting.md        # Common errors and fixes
└── templates/
    ├── Dockerfile.node           # Node.js/TypeScript multi-stage
    ├── Dockerfile.python         # Python multi-stage
    ├── Dockerfile.go             # Go multi-stage (scratch/distroless)
    ├── compose.yaml              # Local dev stack (app + postgres + redis)
    ├── dockerignore              # Universal .dockerignore template
    └── devcontainer.json         # VS Code Dev Container config

Workflow

Follow these phases in order. Stop after each phase to confirm with the user before continuing.

Phase 1: Discover

Goal: Understand the project stack and what needs containerizing.

1. Check for an existing project:

   Read package.json       → Node.js/TypeScript (check for build script, entry point)
   Read requirements.txt   → Python (check for gunicorn/uvicorn)
   Read go.mod             → Go (check module path)
   Read pyproject.toml     → Python (check for poetry/uv)
   Glob Dockerfile*        → existing Docker setup
   Glob compose*           → existing Compose files
   Glob .devcontainer/**   → existing Dev Container
   

2. Identify the key details:

   • Language/runtime: Node.js, Python, Go, or other
   • Package manager: npm/yarn/pnpm, pip/poetry/uv, go mod
   • Build step: Does the app need compilation? (TypeScript, Go, etc.)
   • Entry point: What command starts the app? (node server.js, gunicorn, ./binary)
   • Services needed: Database (PostgreSQL, MySQL, SQLite), cache (Redis), queue (RabbitMQ), etc.
   • Existing Docker files: Any Dockerfile or compose.yaml already present?

3. Choose the appropriate template from templates/:

   • Node.js/TypeScript → Dockerfile.node
   • Python → Dockerfile.python
   • Go → Dockerfile.go
   • Other → Use references/dockerfile-patterns.md to build from scratch

STOP. Confirm the stack, entry point, and which services the user needs.

Phase 2: Dockerfile

Goal: Create a production-grade, multi-stage Dockerfile.

1. Read the appropriate template from templates/ and references/dockerfile-patterns.md.

2. Create the Dockerfile at the project root. Every Dockerfile should include:

   • Multi-stage build: Separate build and runtime stages
   • Layer caching: Copy dependency files BEFORE source code
   • Minimal base image: Use -alpine or -slim variants (not full ubuntu or node:22)
   • Non-root user: Create and switch to a non-root user
   • Health check: Add HEALTHCHECK for HTTP services
   • Signal handling: Use dumb-init or tini for Node.js (PID 1 problem)

3. Create .dockerignore from templates/dockerignore. Customize for the project's language.

4. Key rules from references/dockerfile-patterns.md:

   • Use COPY not ADD (unless extracting tar archives)
   • Use exec form for CMD: CMD ["node", "server.js"] not CMD node server.js
   • Combine apt-get update && apt-get install && rm -rf /var/lib/apt/lists/* in one RUN
   • Pin base image versions: node:22-alpine not node:latest
   • Use npm ci not npm install in Docker builds
   • For Go: CGO_ENABLED=0 for static binaries that run on scratch

STOP. Review the Dockerfile with the user. Verify it builds: docker build -t app .

Phase 3: Compose

Goal: Set up Docker Compose for local development.

1. Read references/compose-patterns.md and templates/compose.yaml.

2. Create compose.yaml (not docker-compose.yml — Compose v2 convention) at the project root:

   • App service: Build from local Dockerfile, bind-mount source for hot reload, forward ports
   • Database service: PostgreSQL/MySQL with health check, named volume for data persistence
   • Cache service (if needed): Redis with health check
   • depends_on with condition: Use condition: service_healthy so the app waits for services to be ready

3. Health check patterns for common services:

   # PostgreSQL
   healthcheck:
     test: ["CMD-SHELL", "pg_isready -U postgres"]
     interval: 10s
     timeout: 5s
     retries: 5
   
   # Redis
   healthcheck:
     test: ["CMD", "redis-cli", "ping"]
     interval: 10s
     timeout: 5s
     retries: 5
   
   # MySQL
   healthcheck:
     test: ["CMD", "mysqladmin", "ping", "-h", "localhost"]
     interval: 10s
     timeout: 5s
     retries: 5
   

4. Key rules:

   • Do NOT include a version: key — it's deprecated in Compose v2
   • Use named volumes for database data (not bind mounts)
   • Use bind mounts for application source code (enables hot reload)
   • Set environment variables via environment: block, not .env files in the image
   • Use restart: unless-stopped for infrastructure services

STOP. Confirm the Compose setup. Verify it starts: docker compose up

Phase 4: Dev Container (optional)

Goal: Add VS Code Dev Container support for reproducible dev environments.

1. Only do this phase if the user wants Dev Container support. Skip otherwise.

2. Read templates/devcontainer.json.

3. Create .devcontainer/devcontainer.json with:

   • Base image or Dockerfile reference
   • VS Code extensions to auto-install
   • Port forwarding for the app and services
   • postCreateCommand for dependency installation
   • remoteUser set to non-root
   • Features for common tools (Docker-in-Docker, CLI tools)

4. If using Compose, reference the compose file:

   {
     "dockerComposeFile": "../compose.yaml",
     "service": "app",
     "workspaceFolder": "/app"
   }
   

STOP. Confirm the Dev Container config. Test by reopening in container.

Troubleshooting Quick Reference

Read references/troubleshooting.md for detailed solutions.

Architecture Notes

• Multi-stage builds are the single most impactful optimization. Build stage has compilers/tools; runtime stage has only the artifact. Typical 80-99% size reduction.
• Layer caching depends on instruction order. Put things that change rarely (system packages) before things that change often (source code). Copy dependency lock files before source code.
• Compose v2 uses docker compose (space, not hyphen). No version: key needed. Health checks + depends_on: condition: service_healthy replaces the old wait-for-it.sh scripts.
• Dev Containers are a spec, not a VS Code feature. They work in Codespaces, DevPod, Gitpod, and any IDE that supports the spec. The .devcontainer/ directory travels with the repo.
• .dockerignore is not optional. Without it, .git/ alone can add hundreds of MB to the build context, and .env files may leak secrets into the image.

Output Summary

After completing all phases, the user should have:

• Multi-stage Dockerfile at project root
• .dockerignore customized for the project stack
• compose.yaml with app + services, health checks, named volumes
• Working docker compose up that starts the full local stack
• (Optional) .devcontainer/devcontainer.json for VS Code / Codespaces