Coyote Point Systems E350GX, Installation And Administration Manual

Page: 243 / 344

Overview of Geographic Load Balancing with Envoy
Equalizer Installation and Administration Guide 239
1. Figure 51 is an illustration of a client in California whose local DNS server has contacted Envoy Site A to
resolve the destination domain name for the client request -- in this example,
www.coyotepoint.com
.
Figure 51 Sending name resolution requests to an Equalizer in a GeoCluster
2. Site A sends a geographic query protocol probe (GQP) to all the other Envoy sites in the GeoCluster for the
requested domain (this GeoCluster has the same name --
www.coyotepoint.com
). The probe is received by a
special Envoy agent running at each site in the cluster (the agent for a site starts when you configure Envoy for
the site). Site A also queries its local Envoy agent (see Figure 52).
Figure 52 The selected Equalizer queries other Equalizers and its own servers in the GeoCluster
The GQP probes contain information about the requesting client and the local resource (i.e., local cluster) that is
being requested by the client.
If
ICMP triangulation
is enabled, the GQP probes also tell the sites to send an ICMP echo request (‘ ping ’) to
the client’s local DNS server, and to return the DNS server’s response time in their GQP response to Site A.
This provides more accurate client location information to Envoy in the case where a resource is available at
more than one site.
Envoy Site B
(West Coast USA)
Envoy Site A
(East Coast USA)
Internet
Envoy Site C
(Europe)
Client
(California, USA)
Client’s
Local DNS
DNS
Authoritative
DNS
for
coyotepoint.com
DNS
Envoy Site B
(West Coast USA)
Envoy Site A
(East Coast USA)
Internet
Envoy Site C
(Europe)
Client
(California, USA)
GQP
GQP
G
Q
P