A web server is provided. The web server includes a communication part for receiving an HTTP request from an entity connected by network and communicating with at least one WAS; and a processor for performing at least one of (i) a process of transmitting the HTTP request received from the entity to a specific WAS selected among the at least one WAS and then receiving information on an HTTP session corresponding to the specific WAS from the specific WAS when receiving an HTTP response from the specific WAS in response to the HTTP request, thereby retaining the information on the HTTP session and (ii) a process of transmitting a PING signal and then receiving the information on the HTTP session corresponding to the specific WAS from the specific WAS when receiving a PONG signal in response to the PING signal, thereby retaining the information on the HTTP session.