1. A method comprising: fetching, by a network management system and from a first network device, configuration data associated with a service executing on the first network device; in response to determining that the service extends across multiple network devices, constructing, by the network management system and based on the configuration data, a first partial service instance associated with the service executing on the first network device; merging, by the network management system, a plurality of partial service instances to form a merged partial service instance, the plurality of partial service instances including the first partial service instance and a second partial service instance associated with the service executing on a different network device; and promoting the merged partial service instance as a service instance.