If you are using a released version of Kubernetes, you should refer to the docs that go with that version.
The latest release of this document can be found [here](http://releases.k8s.io/release-1.1/docs/admin/dns.md).Documentation for other releases can be found at releases.k8s.io.
As of Kubernetes 0.8, DNS is offered as a cluster add-on. If enabled, a DNS Pod and Service will be scheduled on the cluster, and the kubelets will be configured to tell individual containers to use the DNS Service's IP to resolve DNS names.
Every Service defined in the cluster (including the DNS server itself) will be assigned a DNS name. By default, a client Pod's DNS search list will include the Pod's own namespace and the cluster's default domain. This is best illustrated by example:
Assume a Service named foo in the Kubernetes namespace bar. A Pod running
in namespace bar can look up this service by simply doing a DNS query for
foo. A Pod running in namespace quux can look up this service by doing a
DNS query for foo.bar.
The cluster DNS server (SkyDNS) supports forward lookups (A records) and service lookups (SRV records).
The running DNS pod holds 4 containers - skydns, etcd (a private instance which skydns uses), a Kubernetes-to-skydns bridge called kube2sky, and a health check called healthz. The kube2sky process watches the Kubernetes master for changes in Services, and then writes the information to etcd, which skydns reads. This etcd instance is not linked to any other etcd clusters that might exist, including the Kubernetes master.
The skydns service is reachable directly from Kubernetes nodes (outside of any container) and DNS resolution works if the skydns service is targeted explicitly. However, nodes are not configured to use the cluster DNS service or to search the cluster's DNS domain by default. This may be resolved at a later time.
See the docs for the DNS cluster addon.