dns-controller creates DNS records
In the bring-up of a new cluster, protokube has already ensured that we have an etcd cluster and an apiserver. It also sets up DNS records for the etcd nodes (this is a much simpler problem, because we have a 1:1 mapping from an etcd node to a DNS name.)
However, none of the nodes can reach the api server to register. Nor can end-users reach the API. In future we might expose the API server as a normal service via Type=LoadBalancer or via a normal Ingress, but for now we just expose it via DNS.
The dns-controller recognizes annotations on nodes.
dns.alpha.kubernetes.io/external will set up records for accessing the resource externally
dns.alpha.kubernetes.io/internal will set up records for accessing the resource internally
The syntax is a comma separated list of fully qualified domain names.