Coyote Point Systems E350GX, Installation And Administration Manual

Page: 244 / 344

Chapter 9: Administering GeoClusters
240 Equalizer Installation and Administration Guide
3. The Envoy agent at each site checks the availability of the requested resource and sends a GQP reply to the
Envoy agent running at Site A (see Figure 53).
Figure 53 The selected Equalizer receives availability and triangulation (latency) information
The content of each response is as follows:
• If the resource (cluster) is not available at the site, the site sends an error message.
• If the resource (cluster) is available at the site, the site sends a message that the resource is available.
• If
ICMP triangulation
is enabled for the GeoCluster, and the requested resource is available at the site, the
site will include the local DNS server’s ICMP echo response time (or lack thereof) in its GQP response to
Site A.
4. After all GQP responses are received (or the GQP probes time out), Site A determine the ‘best available’ site to
return to the client’s DNS server using this process:
a. If at least one GQP probe is received from a site at which the resource is available, then Envoy uses the
resource availability and network latency information (if present) in the GQP replies to select a site for the
client based on the current load balancing policy, and returns the address of the ‘best available’ Envoy site
to the requesting client’s local DNS (see Figure 54).
Figure 54 The client’s local DNS receives the best Equalizer site
Envoy Site B
(West Coast USA)
Envoy Site A
(East Coast USA)
Internet
Envoy Site C
(Europe)
Client
(California, USA)
GQ
P
GQP
G
QP
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