NetScaler high availability using VRRP

Introduction

Laymen explanation

Do you want to setup your website which can scale up with load and also available all the time? If so, you might have considered deployment of load balancer. What if load balancer fails? You may need to ensure high availability of load balancer itself. This document explains how NetScaler load balancer achieves it.

Technical explanation

The Virtual Router Redundancy Protocol (VRRP) is a computer networking protocol that provides for automatic assignment of available Internet Protocol (IP) routers to participating hosts.

Using VRRP (Virtual Redundant Routing Protocol), VIP’s are given different priorities depending on different NetScalers.

Expanding on this concept we can create an N+1 HA configuration. Essentially this leaves one NetScaler that contains all the VIPs in a lower priority as a hot spare.

NetScaler Appliances in Active-Active Mode Using VRRP

In active-active deployment mode, the same VIPs are configured on all NetScaler appliances in the configuration, but with different priorities, so that a given VIP can be active on only one appliance at a time.

The active VIP is called the master VIP, and the corresponding VIPs on the other NetScaler appliances are called the backup VIPs. If a master VIP fails, the backup VIP with the highest priority takes over and becomes the master VIP. All the NetScaler appliances in an active-active deployment use the Virtual Router Redundancy Protocol (VRRP) protocol to advertise their VIPs and the corresponding priorities at regular intervals.

In the following diagram, VIP1, VIP2, VIP3, and VIP4 are configured on appliances NS1, NS2, and NS3. Because of their priorities, VIP1 and VIP 2 are active on NS1, VIP3 is active on NS2 and VIP 4 is active on NS3. If, for example, NS1 fails, VIP1 on NS3 and VIP2 on NS2 become active.

Reference

https://en.wikipedia.org/wiki/Virtual_Router_Redundancy_Protocol

https://wagthereal.com/2011/05/31/citrix-synergy-five-very-cool-things-you-didnt-know-were-possible-with-netscaler/

https://docs.citrix.com/en-us/netscaler/11/networking/interfaces/understanding-netscaler-appliances-in-active-active-mode-using-vrrp.html