How to organize fault-tolerant app?

Trying to find information on the organization of fault-tolerant services. I do not want to reinvent their bikes, I assume that a similar problem has been solved, but little idea which direction to dig. I will try to briefly describe the task.

There are a couple of servers on the windows server (let them be A and b), an application that gathers data from a device U and sends them to subscribers. Servers A and b are physically separated, the device U is located near the server B.

In normal mode, the application runs on the server and collects data from U.
When a disconnection between A and b need to launch the application on the server (switching subscribers - a separate issue), and when connection is restored to complete it.
June 10th 19 at 16:08
1 answer
June 10th 19 at 16:10
It is not clear for what application you want to have fault tolerance, so look at Falovier Cluster or NLB Cluster.

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