Currently , I am doing some research about the load balancer .
On Wikipedia , refer to this link http://en.wikipedia.org/wiki/Load_balancing_(computing).
It says : "Usually load balancers are implemented in high-availability pairs which may also replicate session persistence data if required by the specific application."
Besides , I have also used the search engine to find some related articles about the reason and the cases when we need to use 2 load balancers in a system but I did not find any good information.
So I want to ask why do we need 2 load balancers in most the cases? and which cases we need to use 2 or more load balancers instead of one?
Now a days there is need of implementing applications which are highly available. So in case of load balancer you should have a pairs of load balancer as a highly available pair.
Because if you are using a single server/node load balancer there is a chance it may go down or need to take off for the maintenance. This will cause application downtime or we need to redirect all requests to only one server which will affect the performance severely.
To avoid these things it is always recommended that load balancers should be available in highly available pairs so that load balancer is continuously operational for a desirably long length of time or all the time.