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Feature /

How global load balancers work

Network World, 04/15/02

Global load balancers use proprietary protocols to collect information about the health of a site or to derive basic location information, says Peter Firstbrook, an analyst at Meta Group.

Although there is some support for exchanging metrics between global load-balancing gear using XML, Firstbrook says communications between devices are not expected for a few years, so customers are better off sticking with one vendor for traffic distribution.

Today's global load balancers divert traffic using one or more of several techniques:

  • Most common for Internet applications is DNS redirection, in which the global load balancer becomes the authoritative name server. In this scenario, client URL queries traverse Internet DNSs until the IP address of the

    global load balancer is returned. The appliance then gives the client the IP address of the best data center.

    One disadvantage of DNS redirection is that it is time-sensitive. The appliance might not have the most up-to-date information on the status of each server or database. But DNS redirection is relatively fast and easy to deploy and requires less system intelligence than other methods.

  • DNS redirection is often used in conjunction with HTTP redirection. This method sends traffic to the most available site based on HTTP header information. It's also considered quick to implement, but the downside is that it's only good for HTTP traffic, not for FTP streaming, for example.

  • Triangulation is another DNS method that works when the client sends out a request, which is shipped to multiple sites that contain the requested content. The best available

    server sends back data the fastest. Radware uses a triangulation method where the load balancer directs traffic to the least loaded site, while masking that address with the address of the redirecting site.

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