The Caddyfile shows how you can use caddy to listen on ports 80 & 443 and sit in front of iris webserver(s) that serving on a different port (9091 and 9092 in this case; see Caddyfile).
Running our two web servers
Go to $GOPATH/src/github.com/kataras/iris/_examples/caddy/server1
Open a terminal window and execute go run main.go
Go to $GOPATH/src/github.com/kataras/iris/_examples/caddy/server2
Open a new terminal window and execute go run main.go
Extract its contents where the Caddyfile is located, the $GOPATH/src/github.com/kataras/iris/_examples/caddy in this case
Open, read and modify the Caddyfile to see by yourself how easy it is to configure the servers
Run caddy directly or open a terminal window and execute caddy
Go to https://example.com and https://api.example.com/user/42
Notes
Iris has the app.Run(iris.AutoTLS(":443", "example.com", "mail@example.com")) which does
the exactly same thing but caddy is a great tool that helps you when you run multiple web servers from one host machine, i.e iris, apache, tomcat.