Cardellini, M. Colajanni, P.S. Yu,
``Geographic load balancing for scalable distributed Web systems'',
Proc. 8th Int'l Symp. on Modeling, Analysis and Simulation of
Computer and Telecommunication Systems (MASCOTS'00),
San Francisco, CA, pp. 20-27, Aug./Sep. 2000. IEEE Computer Society.
Users of highly popular Web sites may experience long delays when accessing
Upgrading content site infrastructure from a single node to a locally
distributed Web cluster composed by multiple server nodes provides a limited
relief, because the cluster wide-area connectivity may become the bottleneck.
A better solution is to distribute Web clusters over the Internet by placing
content nodes in strategic locations. A geographically distributed architecture
where the Domain Name System (DNS) servers evaluate network proximity and users
are served from the closest cluster reduces network impact on response time.
On the other hand, serving closest requests only may cause unbalanced servers
and may increase system impact on response time.
To achieve a scalable Web system, we propose to integrate DNS proximity
scheduling with an HTTP request redirection mechanism that any Web server can
activate. We demonstrate through simulation experiments that this further
dispatching mechanism augments the percentage of requests with guaranteed
response time, thereby enhancing the Quality of Service of geographically
distributed Web sites.
However, HTTP request redirection should be used selectively because the
additional round-trip increases network impact on latency time experienced by users.
As a further contribution, this paper proposes and compares various mechanisms
to limit reassignments with no negative consequences on load balancing.
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