I received this Paper a while back and think it is an excellent read. I just copied a random part of the paper to give you an idea of what it covers. There’s not much more to say about it then just read it, it is as in-depth as it can get on FT. I read it several times by now and still discover new things every time I read it.
There are many possible ways to attempt to detect failure of the primary and backupVMs. VMware FT uses UDP heartbeating between servers that are running fault-tolerantVMs to detect when a server may have crashed. In addition, VMware FT monitors thelogging traffic that is sent from the primary to the backup VM and the acknowledgmentssent from the backup VM to the primary VM.