Kubernetes - Namespaces

Posted on 2019-09-10 In Kubernetes

Kubernetes Namespaces

Namespace

Namespace is used to group resources for multiple teams and projects. Kubernetes provides isolation between different namespaces.

Kubernetes starts with three initial namespaces:

default The default namespace for objects with no other namespace
kube-system The namespace for objects created by the Kubernetes system
kube-public This namespace is created automatically and is readable by all users (including those not authenticated). This namespace is mostly reserved for cluster usage, in case that some resources should be visible and readable publicly throughout the whole cluster. The public aspect of this namespace is only a convention, not a requirement.

Create a Namespace

namespace-dev.yaml

apiVersion: v1
kind: Namespace
metadata:
  name: dev
  labels: 
    name: dev

use kubectl apply to create the namespace

1 2	$ kubectl apply -f namespace-dev.yaml namespace/dev created

use kubectl get namespaces command to get all available namespace

$ kubectl get namespaces
NAME              STATUS   AGE
default           Active   12d
dev               Active   89s
kube-node-lease   Active   12d
kube-public       Active   12d
kube-system       Active   12d

Create Resource in a namespace

myapp.yaml: Example to create a deployment in dev namespace

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
  namespace: dev
spec:
  replicas: 2
  selector:
    matchLabels:
      app: myapp
  template:
     ...

To list the deployname in dev namespace

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$ kubectl get deployment -n dev
NAME    READY   UP-TO-DATE   AVAILABLE   AGE
myapp   2/2     2            2           37s

If you don’t want to set the namespace in yaml file, you can set the namespace in the kubectl apply command

1	kubectl apply -f myapp -n dev

To list resources for all namespaces, use --all-namespaces option

# get all deployments
$ kubectl get deployment --all-namespaces

# get all pods
$ kubectl get pods --all-namespaces

Setting Current Namespace

permanently save the namespace for all subsequent kubectl commands in that context.

1	kubectl config set-context --current --namespace=dev

use kubectl config get-contexts to check the current namespace.

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$ kubectl config get-contexts
CURRENT   NAME       CLUSTER    AUTHINFO   NAMESPACE
*         minikube   minikube   minikube   default

Delete a Namespace

1 2	$ kubectl delete namespace dev namespace "dev" deleted

Resources under namespace dev will be deleted.

kubens

ubens is a utility to quickly switch between Kubernetes namespaces. You can download kubens from https://github.com/ahmetb/kubectx and then add kubens to system PATH.

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USAGE:
  kubens                    : list the namespaces
  kubens <NAME>             : change the active namespace

Reference

Namespaces