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Chapter 16. Managing Networks and Traffic
166
• Load Balancing or Content Switching Virtual Servers: According to Citrix NetScaler terminology,
a load balancing or content switching virtual server represents one or many servers on the local
network. Clients send their requests to the load balancing or content switching virtual server’s virtual
IP (VIP) address, and the virtual server balances the load across the local servers. After a GSLB
virtual server selects a GSLB service representing either a local or a remote load balancing or
content switching virtual server, the client sends the request to that virtual server’s VIP address.
• DNS VIPs: DNS virtual IP represents a load balancing DNS virtual server on the GSLB service
provider. The DNS requests for domains for which the GSLB service provider is authoritative can be
sent to a DNS VIP.
• Authoritative DNS: ADNS (Authoritative Domain Name Server) is a service that provides actual
answer to DNS queries, such as web site IP address. In a GSLB environment, an ADNS service
responds only to DNS requests for domains for which the GSLB service provider is authoritative.
When an ADNS service is configured, the service provider owns that IP address and advertises
it. When you create an ADNS service, the NetScaler responds to DNS queries on the configured
ADNS service IP and port.
16.9.1.2. How GSLB Works in CloudPlatform
Global server load balancing is used to manage the traffic flow to a web site hosted on two separate
zones that ideally are in different geographic locations. The following is an illustration of how GLSB
functionality is provided in CloudPlatform: An organization, xyztelco, has set up a public cloud
that spans two zones, Zone-1 and Zone-2, across geographically separated data centers that are
managed by CloudPlatform. Tenant-A of the cloud launches a highly available solution by using
xyztelco cloud. For that purpose, they launch two instances each in both the zones: VM1 and VM2 in
Zone-1 and VM5 and VM6 in Zone-2. Tenant-A acquires a public IP, IP-1 in Zone-1, and configures
a load balancer rule to load balance the traffic between VM1 and VM2 instances. CloudPlatform
orchestrates setting up a virtual server on the LB service provider in Zone-1. Virtual server 1 that is
set up on the LB service provider in Zone-1 represents a publicly accessible virtual server that client
reaches at IP-1. The client traffic to virtual server 1 at IP-1 will be load balanced across VM1 and VM2
instances.
Tenant-A acquires another public IP, IP-2 in Zone-2 and sets up a load balancer rule to load balance
the traffic between VM5 and VM6 instances. Similarly in Zone-2, CloudPlatform orchestrates setting
up a virtual server on the LB service provider. Virtual server 2 that is setup on the LB service provider
in Zone-2 represents a publicly accessible virtual server that client reaches at IP-2. The client traffic
that reaches virtual server 2 at IP-2 is load balanced across VM5 and VM6 instances. At this point
Tenant-A has the service enabled in both the zones, but has no means to set up a disaster recovery
plan if one of the zone fails. Additionally, there is no way for Tenant-A to load balance the traffic
intelligently to one of the zones based on load, proximity and so on. The cloud administrator of
xyztelco provisions a GSLB service provider to both the zones. A GSLB provider is typically an ADC
that has the ability to act as an ADNS (Authoritative Domain Name Server) and has the mechanism to
monitor health of virtual servers both at local and remote sites. The cloud admin enables GSLB as a
service to the tenants that use zones 1 and 2.