How to push requests in queue and pull(execute) request when server(Amazon EC2 instance) is free

I have deployed my web service on EC2 (m3.large) windows instance. The service requires 8 GB of ram and 75% of CPU for one request for about 10 minutes. If meanwhile another request comes I want to hold this new request until previous request process completes. If previous request completes then I need to start the held request. And so on.