### Rancher and Kubernetes 1.3
We’ve very excited about Kubernetes 1.3 release, and all the new features that are included with it. There are two that we are especially interested in: Stateful Apps and Cluster Federation.
#### Kubernetes Stateful Apps
Stateful Apps is a new resource to Kubernetes to represent a set of pods in stateful application. This is an alternative to the using Replication Controllers, which are best leveraged for running stateless apps. This feature is specifically useful for apps that rely on quorum with leader election (such as MongoDB, Zookeeper, etcd) and decentralized quorum (Cassandra). Stateful Apps create and maintains a set of pods, each of which have a stable network identity. In order to provide the network identity, it must be possible to have a resolvable DNS name for the pod that is tied to the pod identity as per [Kubernetes design doc](https://github.com/smarterclayton/kubernetes/blob/961f1f94c35d4979ac83bbad482090cb6c22781c/docs/proposals/petset.md):
```
# service mongo pointing to pods created by PetSet mdb, with identities mdb-1, mdb-2, mdb-3
dig mongodb.namespace.svc.cluster.local +short A
172.130.16.50
dig mdb-1.mongodb.namespace.svc.cluster.local +short A
# IP of pod created for mdb-1
dig mdb-2.mongodb.namespace.svc.cluster.local +short A
# IP of pod created for mdb-2
dig mdb-3.mongodb.namespace.svc.cluster.local +short A
# IP of pod created for mdb-3
```
The above is implemented via an annotation on pods, which is surfaced to endpoints, and finally surfaced as DNS on the service that exposes those pods. Currently Rancher simplifies DNS configuration by leveraging Rancher DNS as a drop-in replacement for SkyDNS. Rancher DNS is fast, stable, and scalable - every host in cluster gets DNS server running. Kubernetes services get programmed to Rancher DNS, and being resolved to either service’s cluster IP from 10,43.x.x address space, or to set of Pod ip addresses for headless service. To make PetSet work with Kubernetes via Rancher, we’ll have to add support for Pod Identities to Rancher DNS configuration. We’re working on this now and should have it supported in one of the upcoming Rancher releases.
#### Cluster Federation
Cluster Federation is a control plane of cluster federation in Kubernetes. It offers improved application availability by spreading applications across multiple clusters (the image below is a courtesy of Kubernetes):
