The Active-Passive configuration of the Global Server Load Balancing is a popular solution for organizations that have a production data center and a Disaster Recovery data center. With this configuration, the network traffic is only required to flow into the production data center under normal operations and then diverted to the Disaster Recovery data center, if there is a loss of service for production resources, such as when a Web server is not available.
To ensure that network services are only transferred back to the production data center when all services are ready, you can enable the Disable Primary When Down option on the Global Server Load Balancing VServers that represent the production network services. When there is a loss of service or ability of the network users to access resources at the production location, the network traffic is diverted to the Disaster Recovery data center. If services are restored at the production data center, the network traffic remains diverted to the Disaster Recovery data center until an administrator can manually re-enable the Global Server Load Balancing VServers at the production data center.
This setup does not work as expected if you only enable the Disable Primary When Down option in the Global Server Load Balancing VServers of the production NetScaler appliances. If this option is not enabled in the Global Server Load Balancing VServers of the Disaster Recovery NetScaler appliances, you might observer the following sequence of incidences:
1. The backend Web server that is mapped to the production Global Server Load Balancing service fails a monitor and the status of the Global Server Load Balancing VServer is marked as DOWN.
2. The network traffic is diverted to the Backup VServer, which is the Disaster Recovery Global Server Load Balancing VServer in the Disaster Recovery NetScaler appliance.
3. The backend Web server in the production data center is restored and monitors pass causing the production Global Server Load Balancing VServer to be available.
4. The Disable Primary When Down option is enabled on the production Global Server Load Balancing VServer. Therefore, this VServer does not actively server traffic and continues to advertise the Disaster Recovery Global Server Load Balancing VServer as the active VServer.