A node is a working machine in Kubernetes cluster which is also known as a minion. They are working units which can be physical, VM, or a cloud instance.
Each node has all the required configuration required to run a pod on it such as the proxy service and kubelet service along with the Docker, which is employed to run the Docker containers on the pod created on the node.
They are not created by Kubernetes but they are created externally either by the cloud service provider or the Kubernetes cluster manager on physical or VM machines.
The key component of Kubernetes to handle multiple nodes is the controller manager, which runs multiple kind of controllers to manage nodes. To manage nodes, Kubernetes creates an object of kind node which will validate that the object which is created is a valid node.

Service with Selector

apiVersion: v1
kind: node
metadata:
name: < ip address of the node>
labels:
name: <lable name>
In JSON format the actual object is created which looks as follows −
{
Kind: node
apiVersion: v1
"metadata": 
{
"name": "10.01.1.10",
"labels"
{
"name": "cluster 1 node"
}
}
}

Node Controller

They are the collection of services which run within the Kubernetes master and continuously monitor the node within the cluster on the basis of metadata.name. If all the required services are running, then the node is validated and a newly created pod will be assigned to that node by the controller. If it is not valid, then the master will not assign any pod to it and will wait until it becomes valid.
Kubernetes master registers the node automatically, if –register-node flag is true.
–register-node = true
However, if the cluster administrator wants to manage it manually then it could be done by turning the flat of −
–register-node = false

Kubernetes – Service

A service can be defined as a logical set of pods. It can be defined as an abstraction on the top of the pod which provides a single IP address and DNS name by which pods can be accessed. With Service, it is very easy to manage load balancing configuration. It helps pods to scale very easily.
A service is a REST object in Kubernetes whose definition can be posted to Kubernetes apiServer on the Kubernetes master to create a new instance.

Service without Selector

apiVersion: v1
kind: Service
metadata:
name: Tecklearn_service
spec:
ports:
– port: 8080
targetPort: 31999
The above configuration will create a service with the name Tecklearn_service.

Service Config File with Selector

apiVersion: v1
kind: Service
metadata:
name: Tecklearn_service
spec:
selector:
application: “My Application” ——————-> (Selector)
ports:
– port: 8080
targetPort: 31999
In this example, we have a selector; so in order to transfer traffic, we need to create an endpoint manually.
apiVersion: v1
kind: Endpoints
metadata:
name: Tecklearn_service
subnets:
address:
“ip”: “192.168.168.40” ——————-> (Selector)
ports:
– port: 8080
Within the above code, we have created an endpoint which will route the traffic to the endpoint defined as “192.168.168.40:8080”.

Multi-Port Service Creation

apiVersion: v1
kind: Service
metadata:
name: Tecklearn_service
spec:
selector:
application: “My Application” ——————-> (Selector)
ClusterIP: 10.3.0.12
ports:
-name: http
protocol: TCP
port: 80
targetPort: 31999
-name:https
Protocol: TCP
Port: 443
targetPort: 31998

Types of Services

ClusterIP − This helps in restricting the service withwithin the cluster. It exposes the service withwithin the defined Kubernetes cluster.
spec:
type: NodePort
ports:
– port: 8080
nodePort: 31999
name: NodeportService
NodePort − It will expose the service on a static port on the deployed node. A ClusterIP service, to which NodePort service will route, is automatically created. The service can be accessed from outside the cluster using the NodeIP:nodePort.
spec:
ports:
– port: 8080
nodePort: 31999
name: NodeportService
clusterIP: 10.20.30.40
Load Balancer − It uses cloud providers’ load balancer. NodePort and ClusterIP services are created automatically to which the external load balancer will route.
A full service yaml file with service type as Node Port. Try to create one yourself.
apiVersion: v1
kind: Service
metadata:
name: appname
labels:
k8s-app: appname
spec:
type: NodePort
ports:
– port: 8080
nodePort: 31999
name: omninginx
selector:
k8s-app: appname
component: nginx
env: env_name

Kubernetes – Pod

A pod is a collection of containers and its storage inside a node of a Kubernetes cluster. It is possible to create a pod with multiple containers inside it. For example, keeping a database container and data container within the equivalent pod.

Types of Pod

There are two types of Pods −
• Single container pod
• Multi container pod
Single Container Pod
They can be simply created with the kubctl run command, where you have a defined image on the Docker registry which we’ll pull while creating a pod.
$ kubectl run <name of pod> –image=<name of the image from registry>
Example − We’ll create a pod with a tomcat image which is available on the Docker hub.
$ kubectl run tomcat –image = tomcat:8.0
This can also be done by creating the yaml file and then running the kubectl create command.
apiVersion: v1
kind: Pod
metadata:
name: Tomcat
spec:
containers:
– name: Tomcat
image: tomcat: 8.0
ports:
containerPort: 7500
imagePullPolicy: Always
Once the above yaml file is created, we’ll save the file with the name of tomcat.yml and run the create command to run the document.
$ kubectl create –f tomcat.yml
It will create a pod with the name of tomcat. We can use the describe command along with kubectl to describe the pod.
Multi Container Pod
Multi container pods are created using yaml mail with the definition of the containers.

apiVersion: v1
kind: Pod
metadata:
name: Tomcat
spec:
containers:
– name: Tomcat
image: tomcat: 8.0
ports:
containerPort: 7500
imagePullPolicy: Always
-name: Database
Image: mongoDB
Ports:
containerPort: 7501
imagePullPolicy: Always

Within the above code, we have created one pod with two containers inside it, one for tomcat and the other for MongoDB.
So, this brings us to the end of blog. This Tecklearn ‘Concept of Node, Service and Pod in Kubernetes’ blog helps you with commonly asked questions if you are looking out for a job in DevOps. If you wish to learn Kubernetes and build a career in DevOps domain, then check out our interactive, Continuous Orchestration using Kubernetes Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:

Continuous Orchestration using Kubernetes

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What you will Learn in this Course?

Introduction to DevOps
• What is Software Development
• Software Development Life Cycle
• Why DevOps?
• What is DevOps?
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• How DevOps is related to Agile Delivery
• DevOps Implementation
Continuous Orchestration using Kubernetes
• Containers and Container Orchestration
• Introduction to Kubernetes
• Docker Swarm vs Kubernetes
• Kubernetes Architecture
• Deploying Kubernetes using Kubeadms
• Alternate ways of deploying Kubernetes
• Understanding YAML
• Creating a Deployment in Kubernetes using YAML
• Creating a Service in Kubernetes
• Installing Kubernetes Dashboard
• Deploying an App using Dashboard
• Using Rolling Updates in Kubernetes

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