Docker

Docker Compose gives you three ways to split and reuse configurations. They look similar but work at different levels and serve different purposes. Override files: project-level merge Override files are merged with your main compose.yml at the project level. compose.override.yml is loaded automatically; additional files require the -f flag: # compose.override.yml is loaded automatically docker compose up # Explicit merge docker compose -f compose.yml -f compose.prod.yml up Mappings are merged (override wins), arrays are concatenated: ...

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: ...