<p>We have a requirement to setup a geo redundant cluster. I am looking at sharing an external etcd cluster to run two kubernetes clusters. It may sound absurd at first, but the requirements have come down to it..I am seeking some direction to whether it is possible, and if not, what are the challenges.</p>

<p>Yes it is possible, you can have a single etcd cluster and multiple k8s clusters attached to it. The key to achieve it, is to use <code>-etcd-prefix string</code> <a href="https://kubernetes.io/docs/reference/command-line-tools-reference/kube-apiserver/" rel="nofollow noreferrer">flag</a> from kubernetes apiserver. This way each cluster will use different root path for storing its resources and avoid possible conflict with second cluster in the etcd. In addition to it, you should also setup the appropriate rbac rules and certificates for each k8s cluster. You can find more detailed information about it in the following article: <a href="http://%20https://banzaicloud.com/blog/etcd-multi/" rel="nofollow noreferrer">Multi-tenant external etcd for Kubernetes clusters</a>. </p>

<p>EDIT: Ooh wait, just noticed that you want to have those two clusters to behave as master-slave. In that case you could achieve it by assign to the slave cluster a read-only role in the etcd and change it to read-write when it has to become master. Theoretically it should work, but I have never tried it and I think the best option is to use builtin k8s mechanism for high-availability like leader-election.</p>
