Docker Fundamentals
Installation
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Ubuntu - official method
curl -fsSL https://get.docker.com -o get-docker.sh
sudo sh get-docker.sh
sudo usermod -aG docker $USER
newgrp docker # Apply group without logout
Verify
docker --version
docker run hello-world
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Essential Commands
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Images
docker pull nginx # Pull from Docker Hub
docker pull nginx:1.25 # Specific version
docker images # List local images
docker rmi nginx # Remove image
docker image prune # Remove unused images
Containers — Run
docker run nginx # Run (foreground, blocks terminal)
docker run -d nginx # Detached (background)
docker run -d -p 8080:80 nginx # Map host:container port
docker run -d --name mynginx nginx # Named container
docker run --rm nginx # Auto-remove when stopped
docker run -it ubuntu bash # Interactive terminal
docker run -e DB_HOST=localhost myapp # Environment variable
Containers — Manage
docker ps # Running containers
docker ps -a # All containers (including stopped)
docker stop mynginx # Graceful stop (SIGTERM)
docker kill mynginx # Force stop (SIGKILL)
docker start mynginx # Start stopped container
docker restart mynginx
docker rm mynginx # Remove stopped container
docker rm -f mynginx # Force remove running container
Inspect
docker logs mynginx # Container logs
docker logs -f mynginx # Follow logs
docker logs --tail 100 mynginx # Last 100 lines
docker exec -it mynginx bash # Shell into running container
docker exec mynginx nginx -t # Run command in container
docker inspect mynginx # Full container details (JSON)
docker stats # Live resource usage
docker top mynginx # Processes in container
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Writing Dockerfiles
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Example: Node.js application
Base image - always use specific versions in production
FROM node:20-alpine
Set working directory inside container
WORKDIR /app
Copy package files first (layer caching optimization)
COPY package*.json ./
Install dependencies
RUN npm ci --only=production
Copy application code
COPY . .
Create non-root user (security best practice)
RUN addgroup -g 1001 -S nodejs && \
adduser -S nodeuser -u 1001
USER nodeuser
Document which port the app uses (informational)
EXPOSE 3000
Health check
HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
CMD curl -f http://localhost:3000/health || exit 1
Command to run
CMD ["node", "server.js"]
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\\\`bash
Build the image
docker build -t myapp:1.0 .
docker build -t myapp:latest -f Dockerfile.prod .
Tag and push
docker tag myapp:1.0 myregistry.io/myapp:1.0
docker push myregistry.io/myapp:1.0
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Docker Volumes
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Named volumes (managed by Docker, best for databases)
docker volume create dbdata
docker run -d -v dbdata:/var/lib/mysql mysql:8
Bind mounts (host path, best for development)
docker run -d -v /host/path:/container/path nginx
docker run -d -v $(pwd):/app node:20 npm run dev
tmpfs (in-memory, for sensitive data)
docker run -d --tmpfs /tmp:noexec,size=100m myapp
Volume commands
docker volume ls
docker volume inspect dbdata
docker volume rm dbdata
docker volume prune # Remove unused volumes
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Docker Networks
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Network types
bridge - default, containers communicate via IP
host - container uses host network (no isolation)
none - no network
overlay - multi-host (Swarm/Kubernetes)
Create custom network
docker network create mynet
docker network create --driver bridge --subnet 172.20.0.0/16 mynet
Connect containers
docker run -d --network mynet --name app myapp
docker run -d --network mynet --name db mysql:8
Now 'app' can reach 'db' by hostname 'db'!
Commands
docker network ls
docker network inspect mynet
docker network connect mynet existing-container
docker network disconnect mynet existing-container
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