Kubernetes also has an additional construct for isolation at the cluster level. In most cases, you can run Kubernetes and never worry about namespaces; everything will run in the default namespace if not specified. However, in cases where you run multitenancy communities or want broad-scale segregation and isolation of the cluster resources, namespaces can be used to this end.
To start, Kubernetes has two namespaces—default and kube-system. The kube-system namespace is used for all the system-level containers we saw in Chapter 1, Introduction to Kubernetes, in the Services running on the minions section. The UI, logging, DNS, and so on are all run in kube-system. Everything else the user creates runs in the default namespace. However, our resource definition files can optionally specify a custom namespace. For the sake of experimenting, let's take a look at how to build a new namespace.
First, we'll need to create a namespace definition file like the one in this listing:
apiVersion...
