Hi,
what would you recommend to run multiple virtual RouterOS machines?
An VMWare ESXi host with RouterOS machines or a RouterOS installation with KVM machines inside the main ROS installation?
RE!
from licensing point of view, go with RouterOS host with KVM guests.
RouterOS KVM guests that are running as guests on RouterOS will inherit license from host RouterOS. while guests on other VMS require license each.
But 
if they are in ESX then can be vmotioned and auto restarted …
AlexS: I agree; but the main concern I have is the ROS version mismatch as according to documentation it is “recommended” to have the same versions across host/guest ROS and to maintain that - i.e. to remember always to upgrade all guests and after that the host installation, could bite someone in the a.. sometime.
RouterOS running as KVM guest inside RouterOS should run fine with different versions. at least older version running on newer RouterOS, like V6 host running v5 guest. (latest releases should be used)
ROS is 32bit only. it’s ok, until you do not want to run a “full fledged” server on top of it in a kvm, as 32bit gives you only up to 2Gigs of ram.
while ROS guests are just fine with 64M ram, anything bigger (db server, whatever) needs more, so you may run out of resources.
also worthwhile to mention, that unlike other KVM installations, you can’t have mirrored “datastore” in ROS. whereas you can present two disk images from two standalone disks towards the VM and do mirroring there.
but ROS guests can run just fine off from a simple USB thumb drive, so you can have a real diskless virtual-router farm.
regarding moving instances from one host to another… for normal servers, yes, could be an option. i prefer moving services though.
if you try to compare any hypervisor/virtualization implementation and routers, you’ll realise, that routerOS may lacks some “virtualisation” features like on-line migration, or multiple host spanning, but definitely sets the limit for the others in networking features. all the rest (vmware, xenserver, hyperV, you-name-id) is a joke when it comes to networking.
Can you please post the image of the metarouter that are you running with tor?