1. A method, comprising: analyzing, by a management engine computer, a service model, the service model specifying a structure of an IT-service and including nodes respectively representing one or more resources of the IT-service, each resource instance being provided by one of one or more resource managers; selecting a first node of the service model; determining one or more resource management rules assigned to the first node; evaluating the resource management rules assigned to the first node on a resource instance catalog, the resource instance catalog indicative of currently existing instances of the one or more resources and their respective allocation to the IT-service for computing selection criteria; applying the selection criteria for selecting one of the one or more resource managers on a service provider catalog; creating an instance of the resource provided by the selected resource manager; and allocating the resource instance to the IT-service.