To avoid configuring every service for high-availability on two servers, you can do surprisingly well with a replicated VM and DRBD or equivalent. In the event

To avoid configuring every service for high-availability on two servers, you can do surprisingly well with a replicated VM and DRBD or equivalent. In the event of unplanned failover, it looks to the VM like an unplanned abrupt reboot took place. In reality it reboots, usually very fast, on the other host. All services running inside can recover in the usual way (journalled filesystems, databases, programs restart), and don't need any high-availability configuration or replicas configured. You do need to ensure I/O is committed durably across the network, including I/O barriers. This is a combination of VM host, filesystem and DRBD config. (It is actually possible to do this with the VM not even seeming to reboot, so network connections and processes are unaffected by the fail-triggered instant migration. This is done by running VMs in synchronised tandem and is a rather more advanced technique. I've never used it.)