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How GSLB works

GSLB is based on the following:

The following figure shows a client using a browser to view the Web site for the Foo Corporation at www.foocorp.com.

The Foo Corporation has two Web sites with WSMs configured for GSLB, and identical content and services--one in Burbank, and one in Denver. The WSMs are also configured as the Authoritative Name Servers for www.foocorp.com.

The following steps describe DNS resolution in the figure above:

  1. The client Web browser requests the www.foocorp.com IP address from the local DNS.
  2. Client's DNS asks its upstream DNS, which in turn asks the next, and so on, until the address is resolved. The request reaches either:
  3. The Foo Corporation's Burbank DNS has been configured to use the local WSM as the authoritative name server for www.foocorp.com.
  4. The Burbank WSM responds to the DNS request with the current best service IP address.
    5. Since each WSM regularly checks and communicates health and performance information with its peers, each can determine which site(s) are best able to serve the client's needs. Each can respond with a list of IP addresses for the Foo Corporation's distributed sites, which are prioritized by performance, geography, and other criteria. In this case, the Burbank WSM knows that Denver currently provides better service, and lists Denver's virtual server IP address first when responding to the DNS request.
  5. The client connects to Denver for the best service.
    6. The client's Web browser uses IP address information obtained from the DNS request to open a connection to the best available site. The IP addresses represent virtual servers which are locally load-balanced according to regular SLB configuration. If the site serving the client HTTP content suddenly experiences a failure (no healthy real servers) or becomes overloaded with traffic (all real servers reach their maximum connection limit), the WSM issues an HTTP Redirect and transparently causes the client to connect to another peer site.

See also:

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