Why I need include port with the domain/ip ?

When you use a URL without a port included your browser assumes it is port 80 (or 443 for HTTPS). Using anything else requires it to be specified. Generally with modern apps using Rails, a JavaScript framework or something other than static HTML or PHP scripts you will use a reverse proxy web server in front of the app to process requests (this also automatically gives you nice standard access logs). What you can do is:

First install nginx

sudo apt-get update;
sudo apt-get install nginx;

Then once it’s installed, edit the nginx configuration file in /etc/nginx/sites-enabled/ so it reads like:

server {
        listen   80; 
        server_name example.com; 
        
     location / {      
        proxy_set_header X-Real-IP  $remote_addr;
        proxy_set_header X-Forwarded-For $remote_addr;
        proxy_set_header Host $host;
        proxy_pass http://127.0.0.1:50000;

     }
}

Then restart nginx:

service nginx restart