A Caddy instance configured to reverse-proxy subdomains to hostnames.

Usage

1. Create a dedicated Docker network PUBLIC_NET
2. Connect any containers you'd like to expose to PUBLIC_NET, have them all respond to plain HTTP on this network
3. Connect this container to PUBLIC_NET and expose HTTP and HTTPS ports. Environment variables to be specified:
   • DOMAIN: the domain name under which to proxy subdomains without the wildcard label. (eg. for *.example.com use example.com)
   • DNS: the DNS provider's name as recognized by Lego
   • EMAIL: email address to use in certificates
   • Any environment variables required to configure Lego for your DNS provider
4. Persist /config, /data and /lego using eg. volumes or bind mounts. The first two are managed by Caddy, the third is used to store certificates, secret keys and other related data. Failure to persist this directory may result in hitting Let's Encrypt rate limits, which can prevent you from obtaining TLS certificates for a week

Example command for Linode:

docker run -d --restart always --name auto-gateway \
    -p 80:80 -p 443:443 --net exposed \
    -e DOMAIN=example.com -e EMAIL=webmaster@example.com \
    -e DNS=linode -e LINODE_TOKEN=0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef \
    -v autocaddy_config:/config -v autocaddy_data:/data -v autocaddy_lego:/lego \
    lbfalvy/autocaddy

Note that hostnames are deduced from the request and only ever a single label is matched, so the above example configuration will proxy foo.example.com to foo and caddy.community.example.com to community, however, there's no hostname filtering so all hosts visible from the caddy container under a single-label hostname will be proxied.

To improve security, you can also specify the PORT envvar for forwarded HTTP traffic, so that containers and other hosts accidentally proxied by Autocaddy will fail to respond. This doesn't protect against malicious or compromised hosts able to bind single-label hostnames, it just prevents exposing friendly hosts by mistake.