Hi Rajendra, afaik this "single LEF Active - Pasive" strategy is allowed (be sure that only 1 server is active at all times).
There are a couple things to consider:
1- Unless you are always backing up Server A (Active) to Server B (Pasive) you better set up your Repository Database and Shared Storage in a third place (Server C?) so both Server A and B point to the same configurations, apps, etc.
2- Another strategy could be create an Active - Active structure using multinodes. Server A is the Central Node and Server B is a secondary with all services running and the capability to perform as a temporary Central Node if needed. The recommendations of Server C applies here too.
Best is to discuss with your local Qlik partner.
We sometimes use this technique :
* for cold/hot failovers. As long as there is only one active at a time you should be ok. It requires some technical skills to set it up.
* for connected servers : Connect them via the QMC and let Alik handle the failover should be ok and is within the license agreement.