High availability(HA) works directly between the NetScaler instances of two SD-WAN 4100 or 5100 appliances. As shown in the configuration , the two appliances are configured almost identically, except for management network IP addresses.
If the active appliance becomes unavailable, the passive appliance transparently takes over the function of the primary appliance. This is called “failover.” As a result, disruption of services over the network is minimal. After a failover, all clients must reestablish their connections to the managed servers, but the session persistence rules are maintained as they were before the failover.
HA is supported in all deployment modes, and the HA configuration procedure is the same for all modes. The two appliances should be running identical hardware, licensing, and software releases, and must be deployed identically, using the same deployment modes on the same subnets.
When you enable HA, the configuration of the primary appliance’s NetScaler instance is copied to the secondary appliance as part of the NetScaler HA synchronization process.
To learn more about setting up high availability on a NetScaler instance, see the High Availability node of the Citrix eDocs website.