Updating a single-replica MongoDB cannot demonstrate true power behind Deployments. We need a scalable service. It's not that MongoDB cannot be scaled (it can), but it is not as straight-forward as an application that was designed to be scalable. We'll jump to the second application in the stack and create a Deployment of the ReplicaSet that will create Pods based on the vfarcic/go-demo-2 image. But, before we do that, we'll spend a few moments discussing the need for zero-downtime deployments.
On the one hand, our applications are supposed to have very high availability. Depending on the context and the goals, we usually discuss how many nines are coming after 99%. At the very least, an application must have availability of at least 99.9%. More likely, it should be something closer to 99.99 or even 99.999 percent availability. Hundred...