Abstract: With the rapid growth of Web traffic,making the application of load balancing equipment more and more widely,but the current load balancing equipment is very expensive,leading to small and medium-sized enterprises (SMEs) unbearable,so the design of a low cost Web service load balancer has important significance．The author through the analysis of the current load balancing technology,Constructed the design framework of Web server load balancer,designed algorithms,such as server performance evaluation,health check,continuous service etc,to solve the core problem for SMEs to design the low cost Web server load balancer.

Key words: Web server,Load balancer,NAT,SNMP