http://www.devoperandi.com/vault-in-kubernetes-take-2/
https://www.usenix.org/sites/default/files/conference/protected-files/ucms15_slides_shaikh.pdf
https://www.vaultproject.io/docs/concepts/ha.html
https://kubernetes.io/docs/admin/high-availability/#clustering-etcd
https://kubernetes.io/docs/tasks/tls/managing-tls-in-a-cluster/