Caddy docker-compose.yaml that writes an inline Caddyfile from an environment variable at runtime.

caddy.docker-compose.yaml

# Use a modern compose version
version: '3.8'

services:
  caddy:
    image: caddy:latest
    restart: unless-stopped
    ports:
      # Port 80 for HTTP and ACME (Let's Encrypt) challenges
      - "80:80"
      # Port 443 for HTTPS
      - "443:443"
      # Port 443/udp for HTTP/3
      - "443:443/udp"
    
    volumes:
      # This named volume is crucial for persisting Caddy's state,
      # especially SSL certificates from Let's Encrypt.
      - caddy_data:/data

    environment:
      # Define the Caddyfile content as a multi-line env variable
      CADDYFILE_CONTENT: |
        # --- Your Caddyfile Configuration Goes Here ---

        # Example 1: Simple "Hello World" on port 80
        # (Great for local testing)
        :80 {
          respond "Hello, world from an ENV variable!"
        }

        # Example 2: Automatic HTTPS for your domain
        # (Uncomment and replace with your domain)
        #
        # your-domain.com {
        #   # Serves static files from this directory
        #   root * /usr/share/caddy
        #   file_server
        # }
    
    # Override the default command to:
    # 1. Write the environment variable content to the Caddyfile
    # 2. Run Caddy with that config file
    command: >
      sh -c "echo \"$$CADDYFILE_CONTENT\" > /etc/caddy/Caddyfile && 
             caddy run --config /etc/caddy/Caddyfile"

# This top-level block defines the named volume used above
volumes:
  caddy_data:
    # 'external: false' (the default) means Docker will manage this volume