Bits of .NET

🔧 Configure Containers with Environment Variables

Hardcoded config in image is bad. Environment variables configure containers at runtime. Change without rebuild.

📝 Setting Environment Variables

# Docker run
docker run -e DB_HOST=postgres -e DB_USER=admin myapp

# Dockerfile
ENV DB_HOST=postgres
ENV DB_USER=admin

# Using .env file
docker run --env-file .env myapp

# Docker Compose
services:
  app:
    image: myapp
    environment:
      - DB_HOST=postgres
      - DB_USER=admin
    env_file:
      - .env

# Kubernetes
apiVersion: v1
kind: Pod
spec:
  containers:
  - name: app
    env:
    - name: DB_HOST
      value: postgres

🎯 .env File Example

# .env
DB_HOST=postgres
DB_PORT=5432
DB_USER=admin
DB_PASSWORD=secret
REDIS_HOST=redis
REDIS_PORT=6379
APP_ENV=production
LOG_LEVEL=info

# docker-compose.yml
services:
  app:
    image: myapp
    env_file:
      - .env

# Inside container
# Environment variables are available as process.env

💡 Best Practices

• Never commit .env to Git
• Use .env.example for template
• Secrets: Use Docker secrets or Kubernetes secrets
• Override per environment (dev, staging, prod)
• Validate required environment variables