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EneasLari
EneasLari

Posted on • Originally published at eneaslari.com

🐳 The Complete Guide to Dockerizing a Node.js + Express App with Database & File Uploads

#docker

This guide explains how to build, run, and persist a Node.js + Express application inside Docker — with support for MongoDB, PostgreSQL, and file uploads — and also clarifies the relationship between images, containers, and volumes.

1. Big Picture: Images → Containers → Volumes

If Docker was a kitchen:

Docker Concept Kitchen Analogy Purpose
Image Recipe Instructions + ingredients for your app
Container Prepared Meal A running instance of the recipe
Volume Fridge/Pantry Where persistent ingredients are kept

Key rules:

  • Images are read-only.
  • Containers are ephemeral — delete them, data is gone unless stored in a volume.
  • Volumes survive container restarts and recreate.

Diagram: How They Work Together 

 Image: my-node-app Image: mongo:6 Image: postgres:16 +----------------------+ +---------------------+ +---------------------+ | code + deps | | mongo binary + init | | postgres binary + init| +----------------------+ +---------------------+ +---------------------+ | | | v v v Container: app Container: mongo Container: postgres (ephemeral FS) (/data/db) (/var/lib/postgresql) | | | v v v Volume: uploads Volume: mongo_data Volume: pg_data (user files) (MongoDB storage) (Postgres storage)
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2. Why Use Docker for Node.js Apps

  • Consistent environment for development, testing, and production.
  • No "works on my machine" headaches.
  • Easy to ship and run anywhere.
  • Built-in isolation between services (app, DB, admin tools).

3. Project Structure Example 

myapp/ src/ index.js routes/ package.json Dockerfile docker-compose.yml .env uploads/ # Will be mounted to a volume in production
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4. Dockerfile for Node.js + Express 

FROM node:20-alpine # Create app directory WORKDIR /app # Install dependencies first (layer caching) COPY package*.json ./ RUN npm ci --omit=dev # Copy app code COPY . . # Environment variables ENV NODE_ENV=production ENV PORT=3000 # Create uploads folder and fix permissions RUN mkdir -p /app/uploads && chown -R node:node /app USER node EXPOSE 3000 CMD ["node", "src/index.js"]
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5. docker-compose.yml with MongoDB, PostgreSQL & File Uploads 

services: app: build: . env_file: .env ports: - "3000:3000" volumes: - uploads:/app/uploads depends_on: - mongo - postgres restart: unless-stopped mongo: image: mongo:6 volumes: - mongo_data:/data/db restart: unless-stopped mongo-express: image: mongo-express:1 ports: - "8081:8081" environment: - ME_CONFIG_MONGODB_SERVER=mongo - ME_CONFIG_BASICAUTH=false depends_on: - mongo postgres: image: postgres:16 environment: - POSTGRES_DB=mydb - POSTGRES_USER=app - POSTGRES_PASSWORD=app volumes: - pg_data:/var/lib/postgresql/data restart: unless-stopped pgadmin: image: dpage/pgadmin4:8 ports: - "8082:80" environment: - PGADMIN_DEFAULT_EMAIL=admin@example.com - PGADMIN_DEFAULT_PASSWORD=secret depends_on: - postgres volumes: uploads: mongo_data: pg_data:
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6. Environment File Example (.env) 

NODE_ENV=production PORT=3000 DB_CLIENT=mongo MONGO_URI=mongodb://mongo:27017/mydb # PostgreSQL alternative POSTGRES_URI=postgres://app:app@postgres:5432/mydb
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7. How to Run 

# Build and start all services docker compose up -d --build # Stop everything docker compose down # View logs docker compose logs -f app # Enter app container docker compose exec app sh
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8. Volumes in Practice

  • uploads → holds all user-uploaded files.
  • mongo_data → stores MongoDB’s database files.
  • pg_data → stores PostgreSQL’s database files.

Even if you run:

docker compose down docker compose up -d
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Your DB data and uploaded files remain intact because they’re in named volumes.

9. Security Tips

  • Never commit .env files with passwords to Git.
  • Do not expose DB ports to the internet in production.
  • Use specific image versions (mongo:6.0.13, not just mongo:latest).
  • Run app as a non-root user in Dockerfile.

10. Final Takeaways

  • Image = blueprint for your app.
  • Container = running copy of that blueprint.
  • Volume = persistent storage for data that must survive restarts.
  • Use docker-compose to orchestrate app + DB + admin tools.
  • Always separate dev and prod configs.

121 Docker Commands (with Explanations)

Build the image

docker build -t myapp .
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  • -t myapp → tags the image name.

Run a container

docker run -d --name myapp-container -p 3000:3000 myapp
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  • -d → detached mode.
  • -p 3000:3000 → map port 3000 host → container.

List containers

docker ps
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Stop a container

docker stop myapp-container
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Remove a container

docker rm myapp-container
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List images

docker images
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Remove an image

docker rmi myapp
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List volumes

docker volume ls
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Inspect a volume

docker volume inspect uploads
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Remove a volume

docker volume rm uploads
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12. Running with Docker Compose

Start all services

docker compose up -d --build
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Stop all services

docker compose down
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Stop and remove with volumes

docker compose down -v
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Check logs

docker compose logs -f app
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13. Migrating to Another Server

Backup volumes

docker run --rm -v uploads:/data -v $PWD:/backup alpine \ tar -czf /backup/uploads.tar.gz -C /data . docker run --rm -v mongo_data:/data -v $PWD:/backup alpine \ tar -czf /backup/mongo_data.tar.gz -C /data .
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Restore volumes

docker run --rm -v uploads:/data -v $PWD:/backup alpine \ tar -xzf /backup/uploads.tar.gz -C /data docker run --rm -v mongo_data:/data -v $PWD:/backup alpine \ tar -xzf /backup/mongo_data.tar.gz -C /data
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14. Summary of Best Practices

  • Use named volumes for persistence (DB, uploads).
  • Separate app, DB, and admin into their own containers.
  • Keep sensitive data in .env, not in code.
  • Use docker-compose.yml for multi-service orchestration.
  • Always .dockerignore node_modules if installing inside the container.
  • Avoid running containers as root in production.
  • Use lightweight base images (node:alpine).

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