If you're going to be running Kubernetes outside of a hosted PaaS, you'll need to adopt one of two strategies for running an HA cluster for Kubernetes. In this chapter, we'll go through an example with Stacked masters, and will describe the more complex external etcd cluster method.

In this method, you'll combine etcd and manager (control plane) nodes in order to reduce the amount of infrastructure required to run your cluster. This means that you'll need at least three machines in order to achieve HA. If you're running in the cloud, that also means you'll need to spread your instances across three availability zones in order to take advantage of the uptime provided by spreading your machines across zones.

Stacked masters is going to look like this in your architectural diagrams:

The second option you have builds in more potential availability in exchange for infrastructure complexity. You can use an external etcd cluster in order to create separation for the control plane and the ectd members, further increasing your potential availability. A setup in this manner will require a bare minimum of six servers, also spread across availability zones, as in the first example:

In order to achieve either of these methods, you'll need some prerequisites.