Allocating an instance of a resource to an IT-service includes: analyzing a service model specifying the structure of an IT-service and comprising nodes and resource management rules specifying the management of said node's resource. For each node, the method includes: determining a resource type indicated by said node; determining one or more resource management rules assigned to said node; evaluating the resource management rules assigned to said node on a resource instance catalog and the determined resource type for computing selection criteria; applying the selection criteria on a service provider catalog for selecting one of the one or more resource managers, the service provider catalog being indicative of one or more of the resource managers respectively being operable to provide a resource instance of a given resource type to the IT-service; creating an instance of the resource provided by the selected resource manager; and allocating said instance to the IT-service.