You can deploy two
NetScaler appliances in a high availability configuration, where one unit
actively accepts connections and manages servers while the secondary unit
monitors the first. The NetScaler that is actively accepting connections and
managing the servers is called a primary unit and the other one is called a
secondary unit in a high availability configuration. If there is a failure in
the primary unit, the secondary unit becomes the primary and begins actively
Each NetScaler in a
high availability pair monitors the other by sending periodic messages, called
heartbeat messages or health checks, to determine the health or state of the
peer node. If a health check for a primary unit fails, the secondary unit
retries the connection for a specific time period. For more information about
high availability, see
"High Availability." If a retry does not succeed
by the end of the specified time period, the secondary unit takes over for the
primary unit in a process called failover. The following figure shows two high
availability configurations, one in one-arm mode and the other in two-arm mode.
Figure 1. High
availability in one-arm mode
Figure 2. High
availability in two-arm mode
configuration, both NS1 and NS2 and servers S1, S2, and S3 are connected to the
configuration, both NS1 and NS2 are connected to two switches. The servers S1,
S2, and S3 are connected to the second switch. The traffic between client and
the servers passes through either NS1 or NS2.
To set up a high
availability environment, configure one NetScaler as primary and another as
secondary. Perform the following tasks on each of the NetScalers:
- Add a node.
- Disable high availability
monitoring for unused interfaces.