Configure high availability 编辑

You can deploy two Citrix ADC appliances in a high availability configuration, where one unit actively accepts connections and manages servers while the secondary unit monitors the first. The Citrix ADC appliance 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 Citrix ADC appliance 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

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.

To set up a high availability environment, configure one ADC appliance as primary and another as secondary. Perform the following tasks on each of the ADC appliances:

• Add a node.
• Disable high availability monitoring for unused interfaces.

Add a Node

A node is a logical representation of a peer Citrix ADC appliance. It identifies the peer unit by ID and NSIP. An appliance 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.

Through CLI

To add a node by using the command line interface, follow these steps:

At the command prompt, type the following commands to add a node and verify that the node has been added:

• add HA node <id> <IPAddress>

• show HA node <id>

  Example

   add HA node 0 10.102.29.170
    Done
   > show HA node 0
   1)      Node ID:      0
           IP:   10.102.29.200 (NS200)
           Node State: UP
           Master State: Primary
           SSL Card Status: UP
           Hello Interval: 200 msecs
           Dead Interval: 3 secs
           Node in this Master State for: 1:0:41:50 (days:hrs:min:sec)
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