Magic of Namespaces in Kubernetes

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Being a container-orchestration system for automating application deployment, Kubernetes is adopted and highly practiced by many teams and that is where namespaces emerge. Namespaces in Kubernetes enables smooth and secure management with effective usage of isolated resources without overlapping.

As it becomes important for a cluster manager or a cluster-admin to split numerous cluster components or objects or resources into smaller distinct groups.

What is a Namespace?

A namespace can be considered as a logically isolated virtual cluster inside the Kubernetes cluster which is from each other.

Each Kubernetes namespace provides a different scope which means that using the combination of an object name and a Namespace, each object gets a unique identity across the cluster.

It helps a lot when multiple teams are using the same cluster and there is a potential of ambiguity. It can be seen as a virtual wall between multiple clusters.

Lets look for namespaces in Kubernetes

To list the namespaces in your cluster you can use the following command.

$ kubectl get namespaces
OR
$ kubectl get ns

By default, a Kubernetes cluster has following namespaces:

default: it has unbounded CPU and memory requests/limits and used by default for creating resources.
kube-public: its a namespace for resources that are publicly readable by all users and is reserved for cluster usage.
kube-system: used by Kubernetes systems/control plane.

Creating namespace in Kubernetes

You can use either the ad-hoc command or the config file to create a namespace.

//creating namespace with single command
$ kubectl create namespace dev-ns
namespace/dev-ns created

Also you can use the below example to create a namespace

apiVersion: v1
kind: Namespace
metadata:
  name: prod-ns
  labels:
    team: prod

Now let’s create resources

Namespace is specified under the metadata, otherwise the default is used .

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

Now lets get the pods and see the output

// as namespace is not specified while getting pods
$ kubectl get pods
No resources found in default namespace.

$ kubectl get pods --namespace dev-ns
NAME        READY   STATUS    RESTARTS   AGE
nginx-pod   1/1     Running   0          2m37s

Setting the namespace preference

To view the namespace you are currently using :

$ kubectl config get-contexts

Now to change the default namespace use following command :

//changes from default to dev-ns ( created earlier)
$ kubectl config set-context --current --namespace=dev-ns

//to validate the change use this command
kubectl config view --minify | grep namespace:

Inter-Namespace communication

Namespaces are isolated from each other, but service in one namespace can still talk to a service in another namespace.

For example, consider frontend and backend as services in different namespaces need to communicate with each other.

In this case, you can use the built-in DNS service discovery provided by Kubernetes and just point your app by its FQDN (fully qualified domain name).

Syntax for it :

<service-name>.<namespace>.svc.cluster.local

Here note that namespaces don’t provide any kind of isolation on running objects.

Cleaning resources created

//to delete a specific pod in a namespace
$ kubectl delete pod nginx-pod --namespace dev-ns

//to delete  all resources in a namespace
$ kubectl delete all --all --namespace dev-ns

//to delete namespace (pods will be deleted automatically)
$ kubectl delete ns dev-ns

Summary

Namespaces are essential objects for dividing and managing Kubernetes clusters which allow us to logically segregate and assign resources to individual users, teams, or applications for a diverse set of workloads.