Great to see! StatefulSet's are an example of how Kubernetes is enabling applications of all types to run on cluster. This doesn't mean the user can't take zero action to port to Kubernetes, the application needs to be running in a container of course, but it is proof that an application doesn't need to be "12 Factor" to run on Kubernetes.
Essentially I see the world broken down into four potential application types:
1) Stateless applications: trivial to scale at a click of a button with no coordination. These can take advantage of Kubernetes deployments directly and work great behind Kubernetes Services or Ingress Services.
2) Stateful applications: postgres, mysql, etc which generally exist as single processes and persist to disks. These systems generally should be pinned to a single machine and use a single Kubernetes persistent disk. These systems can be served by static configuration of pods, persistent disks, etc or utilize StatefulSets.
2) Static distributed applications: zookeeper, cassandra, etc which are hard to reconfigure at runtime but do replicate data around for data safety. These systems have configuration files that are hard to update consistently and are well-served by StatefulSets.
3) Clustered applications: etcd, redis, prometheus, vitess, rethinkdb, etc are built for dynamic reconfiguration and modern infrastructure where things are often changing. They have APIs to reconfigure members in the cluster and just need glue to be operated natively seemlessly on Kubernetes, and thus the Kubernetes Operator concept https://coreos.com/blog/introducing-operators.html
You can see more from about Operators in my short KubeCon keynote here: https://youtu.be/Uf7PiHXqmnw?t=11
Overall, great progress in Kubernetes v1.5! Great to see critical features moving from Alpha to Beta.
Essentially I see the world broken down into four potential application types:
1) Stateless applications: trivial to scale at a click of a button with no coordination. These can take advantage of Kubernetes deployments directly and work great behind Kubernetes Services or Ingress Services.
2) Stateful applications: postgres, mysql, etc which generally exist as single processes and persist to disks. These systems generally should be pinned to a single machine and use a single Kubernetes persistent disk. These systems can be served by static configuration of pods, persistent disks, etc or utilize StatefulSets.
2) Static distributed applications: zookeeper, cassandra, etc which are hard to reconfigure at runtime but do replicate data around for data safety. These systems have configuration files that are hard to update consistently and are well-served by StatefulSets.
3) Clustered applications: etcd, redis, prometheus, vitess, rethinkdb, etc are built for dynamic reconfiguration and modern infrastructure where things are often changing. They have APIs to reconfigure members in the cluster and just need glue to be operated natively seemlessly on Kubernetes, and thus the Kubernetes Operator concept https://coreos.com/blog/introducing-operators.html
You can see more from about Operators in my short KubeCon keynote here: https://youtu.be/Uf7PiHXqmnw?t=11
Overall, great progress in Kubernetes v1.5! Great to see critical features moving from Alpha to Beta.