About vCNS, I use https://fqdn
But unfortunately, this morning my vCenter endpoint has an error, so vCNS is down too 
DC: 659e6c49-c853-44fd-bd59-406718c332fd: inventory: LAB-vcenter: LAB-Cluster: Error processing data collection response, StatusID = 959cacac-d8bc-44d8-9718-fab88b75fc7c, exception: Object reference not set to an instance of an object.
Do you have a specific use case ? because on vCNS it seems very limited ...