[tanelpoder]

VMware even has a vSphere Fault Tolerance product that creates a "live shadow instance" of a VM that mirrors the primary virtual machine (with up to 4 vCPUs). So you can do a quick failover in case of an "immediate planned" failover case, but apparently even when the primary DB goes down. I guess this might work when some external system (like a storage array) goes down in the primary, you can just switch to the other VM (with latest memory/CPU state) and replay that I/O there and keep going... But if there's a hard crash of the primary, if it actually does work, then they must be doing lots of reasoning about internal state change ordering & external device side-effect (somewhat like Antithesis, but for a different purpose). Back in the day, they supported only uniprocessor VMs (with something called vLockstep) and later up to 4 vCPUs with something called Fast Checkpointing.

I've always wanted to test this out for fun, by now 15 years have gone by and I've never got to it...

https://www.vmware.com/products/cloud-infrastructure/vsphere...

[umachin]

VMware has also had a patent on live VM cloning (called it VMfork) for quite a few years now. I worked on the team that built related features. Feature itself was in the desktop product. https://blogs.vmware.com/euc/2016/02/horizon-7-view-instant-...

Live migration had some very cool demos. They would have an intensive workload such as a game playing and cause a crash and the VM would resume with 0 buffering.