Create Kubernetes Deployment, Services & Pods Using Kubectl

We can deploy the application in kubernetes by creating deployment, services and pods using kubectl command or using yaml configuration files. In this tutorial, I will explain you how to create Kubernetes Deployment, Pods and Service using Kubectl.

In the previous posts, already we have explained the below topics. Refer those links to understand this topic from basics.

What is Kubernetes - Learn Kubernetes from Basics
How to Install Kubernetes Cluster with Docker on Linux
Create Kubernetes YAML for Deployment, Service & Pods
What is Docker - Get Started from Basics - Docker Tutorial
What is Container, What is Docker on Container - Get Started
How to Install Docker on CentOS 7 / RHEL 7
Docker Images Explained with Examples - Docker Tutorial
How to Run Docker Containers - Explained with Examples

Let's get started.

What is Deployment in Kubernetes?
Deployment is a controller which manages the pods and It ensures the desired number of pods are always running.

What is Pod in Kubernetes?
Pod is a group of one or more containers for an application which runs on worker (minion) nodes.

For example, Let's create a deployment controller for httpd web server, It would run a single container within a pod using a docker image "httpd" and it will listen on port 80.

Our Lab Setup:

How to Create Deployment and Pods?
Once you have Working Kubernetes Cluster environment, Use "kubectl" command to create a Kubernetes Deployment. Else, Refer this article how to install kubernetes cluster on Linux.

[root@kubernetes-master ~]# kubectl run my-httpd --image=httpd --replicas=1 --port=80
deployment.apps/my-httpd created

Where, "kubectl run" is the command to run the deployment.
"my-httpd" - Used to define the name of the deployment controller
"--image=httpd" - Used to specify which image to be used for the container.
"--replicas=1" - Used to specify number of pods(replication) to be running.
"--port=80" - Used to specify the pods to listen on port 80 locally.

Check the status of deployment
Use "kubectl get deployment" command to display the status of deployments created.

[root@kubernetes-master ~]# kubectl get deployment
NAME       DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
my-httpd   1         1         1            1           30m

Above command gives us the status of deployment with,
NAME - Name of the deployment,
DESIRED - Number of Desired Pods,
CURRENT - Number of Current Pods,
UP-TO-DATE - Number of Pods are up-to-date,
AVAILABLE - Number of Pods are available
AGE - How long the pods are running.
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Also you can use above command with "-o wide" option to get additional details,
CONTAINERS - List of containers associated to this pods
IMAGES - List of Images used in this pods
SELECTOR - Name of the selectors.

[root@kubernetes-master ~]# kubectl get deployment -o wide
NAME           DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE       CONTAINERS     IMAGES            SELECTOR
my-httpd       1         1         1            1           32m       my-httpd       httpd             run=my-httpd

Check the status of Pods
Use "kubectl get pod" command to display the status of pods.

[root@kubernetes-master ~]# kubectl get pod
NAME                            READY     STATUS    RESTARTS   AGE
my-httpd-85fc77d457-cr8jl       1/1       Running   0          37m

Above command gives us the status of pods with,
NAME - Name of the pod,
READY - How many pods are ready out of total pods.
STATUS - Status of pods
RESTARTS - How many times it has restarted
AGE - How long the pods are running.

Again use "-o wide" option to get additional details,
IP - IP address of the pod assigned from the CIDR range been set already during the kubernetes setup, this IP address can be used to access the pod.
NODE - Name of the node on which pod is running.
NOMINATED - Name of the Reserved node.

[root@kubernetes-master ~]# kubectl get pod -o wide
NAME                            READY     STATUS    RESTARTS   AGE       IP           NODE                                  NOMINATED NODE
my-httpd-85fc77d457-cr8jl       1/1       Running   0          51m       172.16.1.2   kubernetes-client1.learnitguide.net   <none>

From above output, our "my-httpd" pod is running on worker node "kubernetes-client1.learnitguide.net" and it has got IP Address "172.16.1.2". So we would be able to access the httpd web server through this IP Address "172.16.1.2" only from the worker node "kubernetes-client1.learnitguide.net".

Let's Login into the Worker node "kubernetes-client1.learnitguide.net" and use "curl" command to check the pods are working fine and accessible.

[root@kubernetes-client1 ~]# curl 172.16.1.5:80
<html><body><h1>It works!</h1></body></html>
[root@kubernetes-client1 ~]#

As expected, it's working from the worker node. Lets create a service to expose the ports externally. so that, any users can access the pods from other systems.

What is Service in Kubernetes?
Service is an endpoint that exposes the ports to the outside world and mapped the port to the container port (target port).

Creating Kubernetes Service
Let's Create a Service to expose the deployment "my-httpd" to port 8080 and connects to the containers on port 80, this would assign a random port number. Using that port, we can access this pods externally.

[root@kubernetes-master ~]# kubectl expose deployment my-httpd --port=8080 --target-port=80 --type=LoadBalancer

Check the status of Service to find the random port number.

[root@kubernetes-master ~]# kubectl get svc
NAME         TYPE           CLUSTER-IP       EXTERNAL-IP   PORT(S)          AGE
kubernetes   ClusterIP      10.96.0.1        <none>        443/TCP          5h
my-httpd     LoadBalancer   10.110.252.204   <pending>     8080:31255/TCP   1m

Newly created service has got port number "31255" for "my-httpd" deployment and we know this pod is running on worker node "kubernetes-client1.learnitguide.net". Now we we will be able to access this using the URL "http://kubernetes-client1.learnitguide.net:31255". from other system if you are in the same network.

[root@lab-server ~]# curl http://kubernetes-client1.learnitguide.net:31255
<html><body><h1>It works!</h1></body></html>
[root@lab-server ~]# 

Confused with lot of ports? Simple!

kubernetes-client1.learnitguide.net:31255 --> kubernetes-client1.learnitguide.net:8080 --> 172.16.1.5:80.

This is what the purpose of service, It exposes the ports to the outside world with some random port and mapped the port to the target port, finally it redirects to the actual container port...

That's it, Hope you have got an idea how to create deployments, services and pods in kubernetes cluster.  Going forward we will play more with kubernetes tool. Keep practicing and have fun. Leave your comments if any.

Also refer other articles,

What is Kubernetes - Learn Kubernetes from Basics
How to Install Kubernetes Cluster with Docker on Linux
Create Kubernetes YAML for Deployment, Service & Pods
What is Docker - Get Started from Basics - Docker Tutorial
What is Container, What is Docker on Container - Get Started
How to Install Docker on CentOS 7 / RHEL 7
Docker Images Explained with Examples - Docker Tutorial
How to Run Docker Containers - Explained with Examples

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