Abstract: A technique for operating a group of virtual machines (VMs) includes utilizing a checkpoint procedure to maintain secondary VMs to assume tasks of primary VMs within a cluster in the event of failover. On failover of a first one of the primary VMs, a first one of the secondary VMs assumes the tasks from the checkpoint immediately preceding a failover event. Each of the primary VMs is connected to receive data from remaining ones of the primary VMs via an internal bus and process the data on receipt. Checkpoints for the primary VMs are synchronized. For each of the primary VMs, release to the external bus of data generated on the basis of received internal bus data is prevented until a subsequent checkpoint has occurred. On failover of one of the primary VMs, all of the primary VMs are directed to initiate failover to an associated one of the secondary VMs.