A system for instantiating resources of an IT-service includes a management engine operable to analyze a service model of said IT-service comprising nodes representing the resources and being indicative of a resource type of said represented resources. Each node comprises a generic API not being specific to any particular resource manager and providing an abstract method for instantiating the resource represented by the respective node. For each node, determining the resource types being indicated by said node; evaluating a service provider catalog indicative of resource managers operable to provide a resource of a given resource type and determining an address of each resource manager; selecting one of the resource managers; sending a request to the address of the selected resource manager for a description of a resource-manager-specific API of said resource manager; overriding said abstract method by a resource-manager-specific method for the API; and executing the overridden abstract method.