Cannot add URL (accessible from browser) as direct DataSource

[Demaunt]

i have four docker containers running:

    docker ps
    CONTAINER ID        IMAGE                    COMMAND                  CREATED             STATUS              PORTS                                                                                NAMES
    97b1f0d98b1c        kamon/grafana_graphite   "/usr/bin/supervisord"   25 minutes ago      Up 25 minutes       80-81/tcp, 0.0.0.0:8125->8125/udp, 0.0.0.0:8126->8126/tcp, 0.0.0.0:40001->3000/tcp   kamon-grafana-dashboard
    79b9032b9ed4        engie_image              "nginx -g 'daemon ..."   3 hours ago         Up 3 hours          443/tcp, 0.0.0.0:8080->80/tcp                                                        engie_cont
    0a1fdd8b830c        piha_image               "docker-php-entryp..."   3 hours ago         Up 3 hours          9000/tcp                                                                             piha_cont
    61c8a4c80180        mysql:5.6                "docker-entrypoint..."   3 hours ago         Up 3 hours          0.0.0.0:33061->3306/tcp                                                              diba_cont

2-4 are designed to launch default laravel project that is accessible via:
localhost:8080

The first container was taken from this image:
https://hub.docker.com/r/kamon/grafana_graphite/

Now the idea is to add container (engie_cont) as DataSource.
I login into grafana as user: admin pass: admin, go to add DataSource and get error:

Why can't I add URL (localhost:8080) that is accessible from browser (Chrome) as DataSource?