Setting up a High Availability Pair

Setting up a High Availability Pair

You can deploy two NetScalers 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 accepting connections.

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 time intervals, see the “High Availability” chapter in the Citrix NetScaler Networking Guide.) If a retry does not succeed for the specific time period, the secondary unit takes over for the primary unit in a process called failover. The following diagram shows two high availability configurations, one with NetScalers deployed in one-arm mode and the other with NetScalers deployed in two-arm mode.

High availability in one-arm mode and high availability in two-arm mode

In one-arm configuration, both NS1 and NS2 and servers S1, S2, and S3 are connected to the switch.

In two-arm 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.

Configuring a High Availability Pair for the First Time

To steps 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.

Adding a Node

A node is a logical representation of a peer NetScaler. It identifies the peer unit using a unique ID and its NSIP. A NetScaler uses these parameters to communicate with the peer and track its state. When you add a node, the primary and secondary units exchange heartbeat messages asynchronously. The node ID is an integer that must not be greater than 64.

To add a node using the configuration utility

1. In the navigation pane, expand System and click High Availability. The High Availability page appears in the details pane.

2. Click the Nodes tab. The Nodes page appears in the details pane.

3. Click Add. The Add Node dialog box appears.

4. In the ID text box, type an ID, for example, 3.

5. In the IP Address text box, type an IP Address, for example, 10.102.29.170.

6. Click Create. The node you created appears in the Nodes page.

To add a node using the NetScaler command line

At a NetScaler command prompt, type:

add HA node 3 10.102.29.170

Disabling High Availability Monitoring for Unused Interfaces

The high availability monitor is a virtual entity that monitors an interface. You must disable the monitor for the interfaces that are not connected or being used for traffic. When the monitor is enabled on one of the interfaces and the status of this interface is DOWN, the state of the node becomes NOT UP. In a high availability configuration, a primary node entering a NOT UP state might cause a high availability failover. An interface is marked DOWN under the following conditions:

• The interface is not connected.

• The interface is not working properly.

• The cable connecting the interface is not working properly.

To disable the high availability monitor for an unused interface using the configuration utility

1. In the navigation pane, expand Network and click Interfaces. The Interfaces page appears in the details pane.

2. Select the interface for which the monitor must be disabled.

3. Click Open. The Modify Interface dialog box appears.

4. In HA Monitoring, select the OFF option.

5. Click OK. The Modify Interface dialog box appears.

To disable the high availability monitor for an unused interface using the NetScaler command line

At a NetScaler command prompt, type:

set interface 1/8 haMonitor OFF