When an ESX/ESXi host fails for any reason, all the running hosted VM instances also fail. Practical Redundancy between two guest machines ( virtual instances) is possible, only if the two ESXi host machines are redundant as well.

To achieve practical redundancy and configure High Availability between two ESXi Virtual Machines. For more information, refer to the following link:

www.vmware.com/resources/techresources/402

Junos Space nodes, when running on the same ESXi host Virtual machine, can become part of the Fabric, but practical redundancy cannot be achieved in such a situation.

If the whole Virtual Machine ESXi server goes down, neither of the nodes can become active. Clustered Junos Space nodes are required to be a part of different ESXi hosts and most importantly, these ESXi host machines must have redundancy as well.