Note: Citrix Application Delivery Management (ADM) can be used to create maintenance jobs to simplify the upgrades of ADC appliances. Review this blog to know 10 ways Citrix ADM supports easier ADC upgrades

Please check below videos for more information

• How to upgrade Citrix ADC using Citrix ADM Service (Video)

• Simplified Citrix ADC Upgrade via Citrix Application Delivery Management Service (Video)

Q: What are the communication ports used between the secondary and primary ADC appliance?

A: Refer to CTX101810 - Communication Ports Used by Citrix Technologies for detailed list of communication ports used between the secondary and primary ADC appliance.

Q: What information is synchronized between both ADC appliances?

A: It synchronizes the ns.conf file and session tables. The synchronization interval is by default three seconds. However, the interface details and channel information in the ns.conf file are not synchronized.

Q: What is the importance of a VMAC connection in a ADC High Availability setup?

A: With the help of virtual MAC (VMAC), there is no need for the ADC appliance to update the ARP entry on an upstream/downstream switch. GARP packets are still sent by default to update the CAM entry on the switches. This helps when the primary appliance in the High Availability setup goes down and you have a large list of unique IP addresses. The nsapimgr command can enable/disable GARP packets for interfaces with a VRID bound. This command and instructions for use can be provided by Citrix Support if it is required for use in your environment.

Q: What is the default behavior of ADC High Availability propagation?

A: By default, High Availability propagation is enabled.

Q: What is HAMON in NetScaler used for?

A: HAMON is used to monitor the health of an interface. If the interface is unhealthy or cannot serve traffic for some reason, you might want to failover, that is when you enable the HAMON on the interface.

Q: Which ADC node should I use to run configuration commands?

A: All commands, other than the interface and channel setting commands must be run on the primary appliance.

Q: What is the recommended procedure for upgrading/downgrading a ADC High Availability setup?

A: Citrix recommends you to perform upgrade/downgrade on the secondary appliance first and then on the primary appliance. For detailed procedure refer to  CTX127455 - How to Upgrade Software on NetScaler Appliances in High Availability Setup.

Q: What is the frequency of sync in a ADC High Availability pair?

A: The sync in a High Availability pair is an event driven process that does not occur periodically. When a new configuration command is issued on the primary appliance, a config propagation takes place to the secondary appliance.
If the incarnation number is different in the Primary and the Secondary appliances for some reason, an High Availability sync takes place.
Note: You can also run the force ha sync command from CLI.

Citrix Documentation - FAQ - High Availability
CTX109013 - Troubleshooting the NetScaler High Availability Issue