One advantage of a cloud offering is its elasticity (i.e., it may grow and shrink its footprint in response to fluctuations in demand). Typically, sets of rules are defined which govern this elastic behaviour. An alternative to rules is the use of an optimisation model and feedback loop. This can provide precise and accurate predictions of resource needs and result in improved adaptive behaviour. Both approaches have their benefits and limitations. A Multi-model Adaptive Cloud Environment (MACE) is introduced in which a cloud manager utilises a hybrid approach, actively switching among models as needed, to drive its provisioning decisions.