A method, in a virtualized system, for balancing a load across multiple virtual machines instantiated over physical hardware of the system, including vertically scaling the capacity of respective ones of the VMs up to a physical capacity limit, LPHY, from an initially allocated physical capacity, LVIRT, by providing access to additional resources of the physical hardware in response to an increased load causing the or each VM to reach or exceed a threshold capacity LT1, and horizontally scaling the capacity of the system by supplementing the multiple VMs with an additional VM instantiated using a hypervisor of the system when a predefined proportion, U1, of the VMs have a capacity LPHY.