nginx.conf

# https://superuser.com/a/1060873
map $http_x_forwarded_for $allowed {
    default false;

    ~(^|,|\s)54.68.161.228$ true;
    ~(^|,|\s)10.200.\d+.\d+$ true;
    "" true;  # for internal-to-internal traffic, X-Forwarded-For is unset
}

server {
    listen       80;
    server_name  localhost;

    location / {
        if ($allowed = false) {
            return 403;
        }
    
        root   /usr/share/nginx/html;
        index  index.html index.htm;
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }
}