CreateTiers.yaml

$ vim web-ns.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: web
  labels:
    tier: web 
$ kubectl apply -f web-ns.yaml
namespace/web created
$ vim middleware-ns.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: middleware
  labels:
    tier: middleware
$ kubectl apply -f middleware-ns.yaml
namespace/middleware created
$ vim database-ns.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: database
  labels:
    tier: database
$ kubectl apply -f database-ns.yaml
namespace/database created
$ kubectl get namespaces --show-labels
NAME              STATUS   AGE     LABELS
database          Active   56s     tier=database
default           Active   10m     <none>
kube-node-lease   Active   10m     <none>
kube-public       Active   10m     <none>
kube-system       Active   10m     <none>
middleware        Active   2m43s   tier=middleware
web               Active   4m11s   tier=web