What is Kubernetes
Kubernetes is an open source, cloud native infrastructure tool that automates scaling, deployment and management of containerized applications.
Kubernetes was originally developed by google and later was handed over to Cloud Native Computing Foundation(CNCF) for enhancement and maintenance. Kubernetes is the most popular and highly in demand orchestrator tool. Kubernetes is complex tool and a bit difficult to learn compare to swarm.
Here are few main architecture components of Kubernetes below:
Cluster
A collection of multiple nodes, typically at least one master node and several worker nodes(also known as minions)
Node
A physical or Virtual Machine(VM)
Control Plane
A component that schedule and deploys application instances across all nodes
Kubelete
An agent process running on nodes. It is responsible of managing the state of each nodes and it can perform several actions to maintain a desired state.
Pods
Pods are basic scheduling unit. Pods consist of one or more containers co-located on a host machine and share same resources.
How to run your first Pod on Kubernetes
Before you begin you need to have a Kubernetes cluster running on your system and kubectl must be configured on it. Kubectl is command line tool which will be communicating with your cluster.
The easiest way to start with it, is get the docker for desktop on windows/Mac. Once you have it you can start docker for desktop and go to settings and you can find Kubernetes label on it. Click it and it will install Kubernetes on your system.
Once done you can run below command to check if Kubernetes cluster is running.
kubectl cluster-info
This command will give you information about your Kubernetes cluster. Now since we checked that our cluster is up and running, we'll deploy our first Pod now.
To check running pods on system run below command:
kubectl get pods
No pods running currently so you'll see no information. To run a Pod execute below command:
kubectl run ng --image=nginx
Here ng is name of Pod I have given. you can give it any name. Now check if Pod is running?
kubectl get pods
NAME READY STATUS RESTARTS AGE
ng 1/1 Running 0 98s
So our first Pod is running.
A Pod can run more than one container in it. Behind the scene you are actually running a container with added abstraction layer which is called a Pod. But remember you can't have more than one container with same name inside a Pod.
You can add -o wide in you get Pod command to get more information about running Pods.
kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
So you get more info.
Note:
kubectl get pods will check running Pods in default Namespace. Kubernetes has a concept of Namespace. So you can have multiple namespaces. When you install Kubernetes so by default the are two namespaces.
- Default
- kube-system
kubectl get pods --all-namespaces -o wide
By running above command you can see all Pods running on all different namespaces.
What are some more flags/options in running a pod?
#Start a single instance of busybox and keep it in the foreground, don't restart it if it exits.
Command Below:
kubectl run -i --tty busybox --image=busybox --restart=Never
# Start a replicated instance of nginx.
Command Below:
kubectl run nginx --image=nginx --replicas=3
Sometimes you need to stop and start the Pod like you do in docker. You stop the container and you start the container. But in Kubernetes, it's not possible to stop the Pod and resume later. You can edit the Pod.yaml file and redeploy your changes. But you also can delete your Pod and easily recreate it.
kubectl delete pod ng
pod "ng" deleted
We have successfully deleted a Pod.
Thats how you can start you first Pod on Kubernetes. Kubernetes is most popular container orchestrator. You can run multiple Pods at scale and monitor them easily. Pods are very essential part of Kubernetes system. So Pods are used to control containers in an indirect manner in Kubernetes. This blog has covered basics of starting a Pod and deleting it.
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