Allocating an instance of a resource to an IT-service includes analyzing a service model specifying the structure of an IT-service and including nodes and resource management rules specifying the management of the node's resource. For each node, a resource type indicated by the node is determined. Resource management rules assigned to the node are also determined. The resource management rules assigned to the node are evaluated on a resource instance catalog for computing selection criteria. The selection criteria is applied on a service provider catalog for selecting a resource manager for providing an instance of the resource. An instance of the resource is created by the selected resource manager and allocated to the IT-service.