Geographic Load Balancing Routing; Distributing The Geographic Load - Coyote Point Systems E350GX Installation And Administration Manual

Chapter 1: Equalizer Overview

Geographic Load Balancing Routing

Envoy routes each incoming request to the site best able to handle it. If a site is unavailable or overloaded, Envoy
routes requests to the other sites in the geographic cluster. When you enable geographic load balancing, Envoy
directs incoming client requests to one of the sites in the geographic cluster based on the following criteria:
• Availability: If a site is unavailable due to network outage, server failure, or any other reason, Equalizer
stops directing requests to that site.
• Performance: Envoy tracks the load and performance at each site and uses this information to determine
the site that can process the request most efficiently.
• Distance: Envoy notes the site that is closest to the client (in network terms) and offers the least network
latency.

Distributing the Geographic Load

Envoy uses the Domain Name System (DNS) protocol
fully-qualified domain names such as
Internet. For Envoy, the authoritative name server for the domain is configured to query the Equalizers in the
geographic cluster to resolve the domain name. When Envoy receives a resolution request, it uses the load-balancing
algorithms configured for the geographic cluster to determine the site that is best able to process the request and then
returns the address of the selected site.
For example, the geographic cluster
coast of the U.S., one on the west coast of the U.S., and one in Europe. The servers at each site are connected to an
Equalizer with the Envoy add-on installed.
Envoy Site B
(West Coast USA)
Figure 2 Three-site geographic cluster configuration
When a client in California attempts to connect to
1. For more information about DNS, see Paul Albitz and Cricket Liu, DNS and BIND, 3rd ed. (O'Reilly & Associates, 1998).
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to perform its geographic load distribution. DNS translates
www.coyotepoint.com
www.coyotepoint.com
Internet
coyotepoint.com
into the IP addresses that identify hosts on the
might have three sites (see Figure 2): one on the east
Envoy Site C
(Europe)
Envoy Site A
(East Coast USA)
:
Equalizer Installation and Administration Guide