monitor incoming http requests to a website with a loadbalancer

I am stuck with the problem of monitoring http requests of a website with an internet-facing loadbalancer. To be specific, I have hosted a website that uses a server farm of AWS EC2 instances with a loadbalancer (ELB) at the front. Now I want to get an idea about the request arrival rate per second (or per minute) to scale the server farm. I want to do this task from unix shell.

Your help would be highly appreciated.