This can also be done with HAProxy

    listen whatismyip
        bind :::80 # listen on ipv4/ipv6
        bind :::443 ssl crt /etc/haproxy/ssl/fullchain.pem
        mode http

        http-request return status 200 content-type "text/plain" lf-string "%[src]" if { path /ip }
        http-request return status 200 content-type "application/json" lf-string "{\"ip\":\"%[src]\"}" if { path /json_ip }
        http-request deny