Kubernetes Namespace Overview

In Kubernetes, namespaces provide a mechanism for isolating groups of resources within a single cluster. Names of resources need to be unique within a namespace, but not across namespaces. Namespace-based scoping is applicable only for namespaced objects (e.g. Deployments, Services, etc.) and not for cluster-wide objects (e.g. StorageClass, Nodes, PersistentVolumes, etc.).

Let's take a practice example

first Create a name space (dev)
then create 2 nginx pod in default name space and dev name space
Then expose the Service to corresponding namespace
Then try to access trough the IP and Fully Qualified Domain name(FQDN)

1. Create a Namespace (`dev`)

kubectl create namespace dev

2. Create Nginx Pods in the Default and Dev Namespaces

For the default namespace:

kubectl create deployment nginx-default --image=nginx

For the dev namespace:

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

3. Expose the Nginx Pods as Services using NodePort

For the default namespace:

kubectl expose deployment nginx-default --type=NodePort --port=80 --target-port=80

For the dev namespace:

kubectl expose deployment nginx-dev --type=NodePort --port=80 --target-port=80 --namespace=dev

4. Let's try to accress through IP Of the pod

First we Enter the we find the pods internal IP's
Default name space Pod IP

  kubectl get pod nginx-default -o wide

  # -----------------output--------------
  : '
  NAME            READY   STATUS    RESTARTS   AGE   IP            NODE       NOMINATED NODE   READINESS GATES
  nginx-default   1/1     Running   0          37m   10.244.0.71   minikube   <none>           <none
  '

dev name space pod IP

  kubectl get pod nginx-dev -n dev -o wide

  # -----------------output--------------
  : '
  NAME        READY   STATUS    RESTARTS   AGE   IP            NODE       NOMINATED NODE   READINESS GATES
  nginx-dev   1/1     Running   0          39m   10.244.0.72   minikube   <none>           <none>
  '

Now we try to reach from default namespace pod(nginx-default) to dev namespace pod (nginx-dev)
Enter The pod First (Enter default namespace pod)
```
  kubectl exec -it nginx-default -- sh
```
Try to reach nginx-dev pod (in dev name space)

  curl 10.244.0.72

  # -----------------output--------------

  : '<!DOCTYPE html>
  <html>
  <head>
  <title>Welcome to nginx!</title>
  <style>
  html { color-scheme: light dark; }
  body { width: 35em; margin: 0 auto;
  font-family: Tahoma, Verdana, Arial, sans-serif; }
  </style>
  </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>

  <p>For online documentation and support please refer to
  <a href="http://nginx.org/">nginx.org</a>.<br/>
  Commercial support is available at
  <a href="http://nginx.com/">nginx.com</a>.</p>

  <p><em>Thank you for using nginx.</em></p>
  </body>
  </html>'

In similar way we can reach different namespace pods through the pod IP's

There is a Problem

If we increase the replica then we have to use service for load balance ,then use specific pod ip is not good way to communicate

5. Let's try to access through service directly

Enter The pod First (Enter default namespace pod)

kubectl exec -it nginx-default -- sh

Out dev name space service was nginx-dev

from our default namespace pod try to reach dev namespace pod through service

 curl nginx-dev

# -----------------output--------------
# curl: (6) Could not resolve host: nginx-dev

Here We directly can not reach one namespace service to another namespace service and Here comes the Fully Qualified Domain name (FQDN)

6. Let's try to accress through FQDN

Instead of service name,we use Corresponding domain name
so first enter the target pod (nginx-dev)
```
  kubectl exec -it nginx-dev -- sh
```
Then find the domain name for this service

   cat /etc/resolv.conf
  # -----------------output--------------
  #nameserver 10.96.0.10
  #search dev.svc.cluster.local svc.cluster.local cluster.local
  #options ndots:5

now From default namespace pod(nginx-default) we try to reach nginx-dev of different namespace(dev) pod

  # curl nginx-dev.dev.svc.cluster.local

  # -----------------output--------------

  : '<!DOCTYPE html>
  <html>
  <head>
  <title>Welcome to nginx!</title>
  <style>
  html { color-scheme: light dark; }
  body { width: 35em; margin: 0 auto;
  font-family: Tahoma, Verdana, Arial, sans-serif; }
  </style>
  </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>

  <p>For online documentation and support please refer to
  <a href="http://nginx.org/">nginx.org</a>.<br/>
  Commercial support is available at
  <a href="http://nginx.com/">nginx.com</a>.</p>

  <p><em>Thank you for using nginx.</em></p>
  </body>
  </html>
  '

💡

Great We learn Basic about the Namespace and how to communicate one namespace to another namespace through the Pod IP's , Through Service with FQDN

Namespace Of Kubernetes

Table of contents

Let's take a practice example

1. Create a Namespace (`dev`)

2. Create Nginx Pods in the Default and Dev Namespaces

3. Expose the Nginx Pods as Services using NodePort

4. Let's try to accress through IP Of the pod

There is a Problem

If we increase the replica then we have to use service for load balance ,then use specific pod ip is not good way to communicate

5. Let's try to access through service directly

6. Let's try to accress through FQDN

Namespace Of Kubernetes

Table of contents

Let's take a practice example

1. Create a Namespace (dev)

2. Create Nginx Pods in the Default and Dev Namespaces

3. Expose the Nginx Pods as Services using NodePort

4. Let's try to accress through IP Of the pod

There is a Problem

If we increase the replica then we have to use service for load balance ,then use specific pod ip is not good way to communicate

5. Let's try to access through service directly

6. Let's try to accress through FQDN

1. Create a Namespace (`dev`)