A proposal of DNS-based adaptive load balancing method for mirror server systems and its implementation

In order to protect a server to become overloading due to concentration of accesses, a mirror server system is widely used for distributing the load to multiservers. For such a system, it is very important for users to select an appropriate one among the servers. In the previous systems, the DNS (domain name system) Round-Robin mechanism is widely adopted for this purpose, otherwise users must choose a server by themselves. Even in the former method, however, since all servers are evenly assigned to clients without any cares of the performance and process status of the servers, the load of each server is deflected. To solve the above problem, this article proposes a new adaptive load balancing method based on the ordinary DNS Round-Robin mechanism. In this proposal, a DNS server for the mirror-server system periodically probes the status of each server. For a query from each client, the DNS server changes its response from the probed results and IP address of the client. Finally, the prototype system of the proposal is implemented and the file transfer speeds of both the proposed method and Round-Robin DNS method are estimated for the mirror server system of RingServer Project in Japan.