"live" mirror of HA VM cluster?
I'm reading about HA techniques in virtualization but all solutions I see work more or less just like more specialized VRRP - when host gets down, VM is booted up on another virtualization host. If storage is shared (eg. iSCSI) then "the same" VM can be booted so to guest OS it looks like kind of power failure. But if there is some important data residing in RAM (for example in-memory database) then it's still lost.
It would be possible though to create snapshot of running VM with some interval (unfortunately it takes plenty of time to create such snapshot so it can't really be done every lets say 10 seconds). Then another virtualization host could load such snapshot and continue running VM "without interruption" (plus minus interval time).
So my question is - are there any solutions automatically "mirroring" VMs in such way that after virtualization host failure VM can be "resumed" on another host without noticeable interruption? Literally like RAID1 of VMs. Mirror that is fully synced on RAM level.
Servers shouldn't "just fail" in the manner you're describing. Most people do not worry about this.
However, this is a use case for VMware Fault Tolerance (FT).
This will do what you're asking for.
If asynchronous replication is desired with a small delay (like 10 seconds), then a solution like Zerto would be apt.
1) Deploy a VMware vSphere cluster and use Fault Tolerance https://www.vmware.com/files/pdf/techpaper/VMware-vSphere6-FT-arch-perf.pdf feature on your virtual machines (as already mentioned above).
2) Deploy a XenServer cluster and use Remus https://wiki.xenproject.org/wiki/Remus.
There are some solutions that can failover VMs without any downtime. At least I know about HPE VSA and Starwinds. They have free versions as well, so you can look at those.
However, I don't know exactly about the first one, ain't tested it by myself yet. About second one - there's an option where you can assign an amount of RAM on the HA device, and this RAM also is replicated on another node. And The VMs failover without reboot. Tested that with Hyper-V cluster.