Coders Classroom: Kubernetes for Developers #21: Kubernetes Namespace in-detail

Kubernetes supports multiple virtual clusters by using Namespaces. It helps when multiple teams using same cluster and want to setup separate Roles, Binding and Environments for each team.

Kubernetes resource name should be unique within a namespace, but not across namespaces. It means, we can use same Pod/Deployment name in different namespaces
Namespaces cannot be nested
Each Kubernetes resource can only be in one namespace. It means, we cannot attach same Pod/Deployment to multiple namespaces
Try to avoid creating namespace with prefix "kube-" as it is reserved for K8 internal system
We can restrict resource usage limit (i.e. CPU, Memory) for each namespace
We can restrict users to access only selected namespaces and it’s Kubernetes objects
By default, all the k8 objects created under "default" namespace

The following four namespaces will be created automatically when the cluster is configured.

Namespace	description
default	By default, all the resources created under “default” namespace without CPU and Memory restrictions
kube-system	This namespace for objects created by the Kubernetes system
kube-public	It is reserved for cluster usage and it is accessible for all users. Use this only when k8 objects should be visible to publicly throughout the cluster
kube-node-lease	It is for lease objects associated with each node to improve performance of the node heartbeats

Create Namespace

from YAML file

apiVersion: v1
kind: Namespace
metadata: 
  name: dev-ns

Save above yaml content as "dev-ns.yaml" and run following kubectl command

// create namespace resoure from yaml file
$ kubectl apply -f dev-ns.yaml
namespace/dev-ns created

// display all namespaces
$ kubectl get ns
NAME              STATUS   AGE
default           Active   30d
kube-node-lease   Active   30d
kube-public       Active   30d
kube-system       Active   30d
dev-ns            Active   17m

// view namespace details using describe command
$ kubectl describe ns dev-ns

// view namespace details as yaml file 
$ kubectl get ns dev-ns -o yaml

2. imperative way

// syntax $kubectl create ns <namespace-name>
$ kubectl create ns dev2-ns
namespace/dev2-ns created

// display all namespaces
$ kubectl get ns
NAME              STATUS   AGE
default           Active   30d
kube-node-lease   Active   30d
kube-public       Active   30d
kube-system       Active   30d
dev-ns            Active   17m
dev2-ns           Active   1m

Create Pod in selected Namespace

from YAML file

we can achieve this by specifying namespace attribute in the metadata section

apiVersion: v1
kind: Pod
metadata:
  name: pod-nginx
  namespace: dev-ns
spec:
  containers:
    - name: nginx
      image: nginx:1.14.2

Save above yaml content as "pod-dev-ns.yaml" and run following kubectl command

// create pod under "dev-ns" namespace using yaml file
$ kubectl apply -f pod-dev-ns.yaml
pod/pod-nginx created

// display all pods from dev-ns namespace
// syntax
$ kubectl get po -n <namespace-name> 

$ kubectl get po -n dev-ns
NAME        READY   STATUS    RESTARTS   AGE
pod-nginx   1/1     Running   0          4m4s

// delete namespace
// all pods gets deleted automatically when namespace is deleted
$ kubectl delete ns dev-ns
namespace "dev-ns" deleted

// display all pods under dev-ns namespace
$ kubectl get po -n dev-ns
No resources found in dev-ns namespace.

// delete all pods without deleting namespace
//syntax:
kubectl delete po --all -n <namespace-name>

$ kubectl delete po --all -n dev2-ns
pod "pod-nginx" deleted

// display all namespaces
$ kubectl get ns
NAME              STATUS   AGE
default           Active   31d
dev2-ns           Active   47m
kube-node-lease   Active   31d
kube-public       Active   31d
kube-system       Active   31d

2. imperative way

// syntax
// kubectl run <pod-name> --image <image-name> -n <namespace-name>
$ kubectl run pod-nginx --image nginx -n dev2-ns
pod/pod-nginx created

// display all pods from dev2-ns namespace
// syntax
kubectl get po -n <namespace-name>

$ kubectl get po -n dev2-ns
NAME READY STATUS RESTARTS AGE
pod-nginx 1/1 Running 0 4m4s

we must use Fully Qualified Domain Name(FQDN) to access Pods from one namespace to another namespace i.e.

<servicename>.<namespace>.svc.cluster.local

Kubernetes for Developers Journey.

Happy Coding :)

2 comments:

prashanthAugust 11, 2021 at 4:19 AM
Hi Rama Subbareddy,

I really appreciate your efforts to get this articles.

I have gone through your kubernetes articles, its only talks about basic concepts. My request is to get real time scenarios like how to autoscaling the POD's and how to deploy pod in specific node. If you provide articles like above scenarios it would be really great..

this is just my suggestion Rama.

Monday, August 9, 2021

Kubernetes for Developers #21: Kubernetes Namespace in-detail

Create Namespace

2. imperative way

// display all namespaces$ kubectl get nsNAME STATUS AGEdefault Active 30dkube-node-lease Active 30dkube-public Active 30dkube-system Active 30ddev-ns Active 17mdev2-ns Active 1m

Create Pod in selected Namespace

2. imperative way

// display all pods from dev2-ns namespace// syntax kubectl get po -n <namespace-name> $ kubectl get po -n dev2-nsNAME READY STATUS RESTARTS AGEpod-nginx 1/1 Running 0 4m4s

2 comments:

// display all namespaces
$ kubectl get ns
NAME STATUS AGE
default Active 30d
kube-node-lease Active 30d
kube-public Active 30d
kube-system Active 30d
dev-ns Active 17m
dev2-ns Active 1m

// display all pods from dev2-ns namespace
// syntax
kubectl get po -n <namespace-name>

$ kubectl get po -n dev2-ns
NAME READY STATUS RESTARTS AGE
pod-nginx 1/1 Running 0 4m4s