Instantiating a resource of an IT-service includes analyzing a service model of the IT-service where the service model includes a node representing a resource for providing the IT-service. A resource type of the resource being indicated by the node is determined, and a service provider catalog is evaluated to determine a resource manager operable to instantiate the resource and an address of the resource manager. A request is sent to the address of the resource manager for a description of a resource-manager-specific API of the resource manager. Upon receipt of the requested description, at least one abstract method for instantiating the resource is overridden with a resource-manager specific method of the resource-manager-specific API, and the resource-manager specific method for instantiating the resource represented by the node is executed.