Docker

Need custom DNS resolution in containers? Use extra_hosts to add hostname mappings without touching system files! Basic extra_hosts usage Add custom host entries to containers: services: app: image: myapp extra_hosts: - "api.local:192.168.1.100" - "db.local:192.168.1.101" - "cache.local:192.168.1.102" Inside the container: docker compose exec app cat /etc/hosts # 127.0.0.1 localhost # 192.168.1.100 api.local # 192.168.1.101 db.local # 192.168.1.102 cache.local Dynamic host resolution Use host machine’s IP dynamically: services: app: image: myapp extra_hosts: - "host.docker.internal:host-gateway" # Magic value! This maps to: ...

Speed up I/O operations and enhance security by using tmpfs for temporary data. RAM-based storage that vanishes on restart! What is tmpfs? Tmpfs is a temporary filesystem that resides in memory: ⚡ Ultra-fast (RAM speed) 🔒 Secure (data doesn’t persist) 🧹 Self-cleaning (cleared on restart) Basic tmpfs usage Simple tmpfs mount: services: app: image: myapp tmpfs: - /tmp - /app/cache - /var/run With size limits: services: app: image: myapp tmpfs: - /tmp:size=100M - /app/cache:size=500M - /var/run:size=10M Advanced tmpfs options Fine-tuned configuration: ...

Know the difference between exec and run! Each has its place in your debugging toolkit. The key difference exec: Runs commands in an existing container run: Creates a new container # Exec: enters running container docker compose exec web bash # Run: starts new container docker compose run web bash When to use exec Use exec for debugging running services: # Debug a running web server docker compose exec web bash # Check logs inside container docker compose exec web tail -f /var/log/app.log # Run database queries docker compose exec db psql -U postgres # Check process list docker compose exec web ps aux # Test connectivity from inside docker compose exec web curl http://api:3000/health Important: Container must be running! ...

Take control of your container logs! Configure different logging drivers for better management, rotation, and analysis. Default logging: json-file By default, Docker uses the json-file driver: services: app: image: myapp logging: driver: json-file options: max-size: "10m" # Rotate after 10MB max-file: "3" # Keep 3 rotated files compress: "true" # Compress rotated files Without rotation, logs can fill your disk! Common logging drivers 1. Local driver (efficient storage) Optimized for performance and disk usage: ...

Speed up builds and reduce image size by managing build contexts effectively. Don’t send unnecessary files to the Docker daemon! Understanding build context The build context is what gets sent to Docker daemon: services: app: build: . # Current directory is the context # Everything in . gets sent to daemon! Check your context size: # See what's being sent docker build --no-cache . 2>&1 | grep "Sending build context" # Output: Sending build context to Docker daemon 458.2MB 😱 Custom build contexts Specify different contexts for different services: ...