GitHub link - https://github.com/SUBHAM-NANDI/40DaysKubernetes/blob/main/Day%2010/Readme.md#step-1-introduction-to-kubernetes-namespaces

Step 1: Introduction to Kubernetes Namespaces

What are namespaces?

Namespaces in Kubernetes provide a mechanism to divide a single cluster into multiple virtual clusters. They allow for separating the resources and objects (like pods, services, and deployments) within a Kubernetes cluster, enabling better organization, isolation, and management of resources.

Why are namespaces important?

• Isolation: Resources in different namespaces are isolated from each other, meaning you can avoid naming conflicts and prevent unwanted interactions between different environments (e.g., dev, test, prod).
• Resource Organization: You can group resources logically based on their environment, application, or ownership.
• Security: Role-Based Access Control (RBAC) can be applied at the namespace level, allowing fine-grained access control.
• Default Namespace: If a namespace is not specified, resources are created in the default namespace. Kubernetes also creates other system namespaces like kube-system, which contains control plane components.

Step 2: Viewing Existing Namespaces

By default, Kubernetes comes with a few namespaces. You can list them using:

kubectl get namespaces

Example output:

NAME              STATUS   AGE
default           Active   1d
kube-node-lease   Active   1d
kube-public       Active   1d
kube-system       Active   1d

• default: The default namespace where resources are created if no namespace is specified.
• kube-system: Contains system-related components (like kube-dns, kube-proxy).
• kube-public: A public namespace that is readable by everyone, used mainly for cluster information.
• kube-node-lease: Tracks the heartbeats of nodes.

Step 3: Creating a New Namespace (Declarative Way)

A namespace can be created either imperatively or declaratively.

Let's first create a namespace declaratively using a YAML file.

1. Create a namespace.yaml file with the following content:

apiVersion: v1
kind: Namespace
metadata:
  name: demo

1. Apply the YAML file to create the namespace:

kubectl apply -f namespace.yaml

Output:

namespace/demo created

1. Verify the namespace was created:

kubectl get namespaces

You should see the newly created namespace demo.

Step 4: Creating a Namespace (Imperative Way)

You can also create a namespace directly using a simple command without a YAML file:

kubectl create namespace demo-imp

Output:

namespace/demo-imp created

Again, verify:

kubectl get namespaces

Both demo and demo-imp namespaces should now be listed.

Step 5: Deploying Resources to Specific Namespaces

Let’s create a Deployment in the newly created demo namespace. By default, resources are created in the default namespace unless specified otherwise. We will use the --namespace or -n flag to target the demo namespace.

1. Create an NGINX deployment in the demo namespace:

kubectl create deployment nginx-demo --image=nginx --namespace=demo

Output:

deployment.apps/nginx-demo created

1. Verify the deployment:

kubectl get deployments --namespace=demo

Output:

NAME         READY   UP-TO-DATE   AVAILABLE   AGE
nginx-demo   1/1     1            1           10s

1. Check the running pods in the demo namespace:

kubectl get pods --namespace=demo

Output:

NAME                          READY   STATUS    RESTARTS   AGE
nginx-demo-5d8fbbf94d-5htgj   1/1     Running   0          12s

Step 6: Accessing Resources in a Namespace

Resources within the same namespace can communicate with each other directly by their name. However, for cross-namespace communication, the Fully Qualified Domain Name (FQDN) must be used.

1. Get the Pod IP for the NGINX pod in the demo namespace:

kubectl get pod -o wide --namespace=demo

Output:

NAME                          READY   STATUS    RESTARTS   AGE   IP            NODE       NOMINATED NODE   READINESS GATES
nginx-demo-5d8fbbf94d-5htgj   1/1     Running   0          1m    10.244.0.5    minikube   <none>           <none>

The IP of the pod is 10.244.0.5.

1. Let’s create another NGINX deployment in the default namespace:

kubectl create deployment nginx-default --image=nginx

Verify the pods:

kubectl get pods --namespace=default

Output:

NAME                              READY   STATUS    RESTARTS   AGE
nginx-default-6b76b5b8ff-7txdh    1/1     Running   0          10s

Step 7: Testing Communication Between Namespaces

Let’s check if the nginx-default pod in the default namespace can communicate with the nginx-demo pod in the demo namespace.

1. Exec into the nginx-default pod in the default namespace:

kubectl exec -it nginx-default-6b76b5b8ff-7txdh --namespace=default -- /bin/sh

Now, from within this shell, try to curl the IP of the NGINX pod in the demo namespace:

curl 10.244.0.5

Output:

<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and working. Further configuration is required.</p>
</body>
</html>

The communication is successful because we used the Pod IP. However, direct DNS-based communication between namespaces requires FQDN.

1. Exit the pod shell:

exit

Step 8: Deleting a Namespace

To delete a namespace, simply use:

kubectl delete namespace demo

Output:

namespace "demo" deleted

This will remove all the resources within the namespace as well.

Step 9: Cleaning Up Resources

To clean up all the resources created in this demo, delete the nginx-default deployment from the default namespace and any other resources you created:

kubectl delete deployment nginx-default
kubectl delete namespace demo-imp