I have created an instance on Amazon EC2 then installed whm and cpnel. I am able to access cpanel just by using my domain name ex. domainname.com/2083 but when i go to my domain
You should login to your AWS EC console then go to the Security Groups and create a custom allow rule for the HTTP traffic (port 80) and also HTTPS traffic (port 443), both on TCP. By default, amazon only allows you ssh access to your amazon instance. If those ports are not listed on the Security Groups, then none of your sites will be accesibile to the public. Since you are able to access cPanel on port 2083 I suppose you already have a tcp rule to permit access on port 2083.