Active-active site deployment

An active-active site consists of multiple active data centers. Client requests are load balanced across active data centers. This deployment type can be used when you have a need for global distribution of traffic in a distributed environment.

All the sites in an active-active deployment are active, and all the services for a particular application/domain are bound to the same GSLB virtual server. Sites exchange metrics through the Metrics Exchange Protocol (MEP). Site metrics exchanged between the sites include the status of each load balancing and content switching virtual server, current number of connections, current packet rate, and current bandwidth usage. The NetScaler appliance needs this information to perform load balancing across the sites.

An active-active deployment can include a maximum of 32 GSLB sites, because MEP cannot synchronize more than 32 sites. No backup sites are configured in this deployment type.

The NetScaler appliance sends client requests to the appropriate GSLB site as determined by the GSLB method specified in the GSLB configuration.

For an active-active deployment, you can configure the following GSLB methods.

  • Round Robin
  • Least Connections
  • Least Response Time
  • Least Bandwidth
  • Least Packets
  • Source IP Hash
  • Custom Load
  • Round Trip Time (RTT)
  • Static Proximity


  • If MEP is disabled, the following GSLB methods default to the Round Robin method. - RTT - Least Connections - Least Bandwidth - Least Packets - Least Response Time
  • In the static proximity GLSB method, the appliance sends the request to the IP address of the site that best matches the proximity criteria.
  • In the Round Trip Time method, the dynamic round trip time (RTT) values are to select the IP address of the best performing site. RTT is a measure of the delay in the network between the client’s local DNS server and a data resource.

GSLB active-active data center topology

In the diagram, Site 1 and Site 2 are active GLSB sites.

GSLB active-active topology

When the client sends a DNS request, it lands in one of the active sites.

If Site 1 receives the client request, the GSLB virtual server in Site 1 selects a load balancing or content switching virtual server and sends the virtual server’s IP address to the DNS server, which sends it to the client. The client then resends the request to the new virtual server at the new IP address.

As both sites are active, the GSLB algorithm evaluates the services at both sites when making a selection as determined by the configured GSLB method.

Active-active site deployment