Abstract : In a virtualized datacenter, the Service Level Agreement foran application restricts the Virtual Machines (VMs) place-ment. An algorithm is in charge of maintaining a placementcompatible with the stated constraints.Conventionally, when a placement algorithm computes aschedule of actions to re-arrange the VMs, the constraintsignore the intermediate states of the datacenter to only re-strict the resulting placement. This situation may lead totemporary violations of the constraints. In this paper, wediscuss the causes of these violations. We then advocatefor continuous placement constraints to restrict also the ac-tions schedule. We discuss why their development requiresmore attention and how the extensible placement algorithmBtrPlace can address this issue.