Kubernetes – An Open-Source Container Management Framework

What is Docker

Consider the following real-world example: - A developer would create the application (code) and send it to a tester for evaluation.

The code wouldn't run on the tester system, which is the first issue that surfaces. This occurs as a result of the various computing settings.

We can attempt to create a virtual machine and reproduce the complete environment to get around these issues and make the code function for testers.

Using Docker (containers) is a substitute and effective option.

Virtual machines and Docker (containers) vary primarily in the following ways: (Note that this is only an example.)

The main distinction of Docker is that it employs the same guest OS for each container. As a result, it is lighter and still offers the same benefits.

The advantages and disadvantages of a virtual machine versus Docker

Comparatively speaking, Docker uses less RAM on the host computer than a virtual machine does.

The two have extremely different boot-up times. Docker starts up quicker. Compared to a virtual machine, the Docker environment performs faster and more reliably.

Compared to a virtual machine environment, Docker is also incredibly simple to start up and scale.

Docker is simpler to port across several systems.

When the guest OS is not required, the space allocation difference between Docker and a virtual machine is substantial. Additionally, the Docker environment is by nature smaller because it utilises the same guest OS for each container.

As a developer, you can now build up your solution or application and give it to a tester, and everything will function perfectly since Docker is already operating in their environment.

Docker brings a lot of advantages:

• Isolated
• Consistent
• Cost-effectiveness
• Fast Deployment
• Mobility
• Portability
• Repeatability
• Automation
• RollBack
• Flexibility
• Modularity and
• Scaling

Imagine that the application you have created has to be distributed to some testers or other end users. In other words, one Docker container is created for each of these users. Click here to learn Data Science Course in Chennai

So, what happens if there is an upgrade to the application?

All updates and modifications should be visible to application users as well, therefore each container has to be updated. If done manually, managing all of these containers will be challenging.

We need a framework to facilitate maintenance and operations on the containers. The Kubernetes container management framework was created by Google in 2014.

Let's examine Kubernetes, sometimes referred to as K8s:

A framework and technology called Kubernetes is used to manage distributed containers (microservices). The life cycle of a Docker container is managed by Kubernetes, which consists of a number of distributed components. Data Science Training in Bangalore

Nodes, the Linux machines that Kubernetes operates on, are these machines. Nodes come in two varieties.

• Worker/Slave Node: In charge of running your Docker containers
• Master Node: In charge of managing the cluster's state

The roles of the Kubernetes components operating on these nodes are well specified.

A typical workflow in Kubernetes is:

# List of Components in Kubernetes Cluster:

API Server

• The heart of any Kubernetes cluster.
• It is a REST API.
• It is also stateless.
• The default port it listens to is port 6443 (unlike 80 (http) and 443 (https) requests).
• The resources in Kube-apiserver are:
• Pod
• ReplicaSet
• PersistentVolume
• NetworkPolicy
• Deployment

Note: all are related to container management only.

Etcd

• Distributed NoSQL database
• The main memory of the Kubernetes cluster
• Independent project of Kubernetes
• No Alternative option to Etcd for data storage
• Apiserver calls will read or write data from or to Etcd
• Cluster state information
• Single point of failure - Etcd crashes then Kubernetes cluster is inaccessible
• Not an In-Memory DB. Data is stored on the Disk

Scheduler

• Responsible for electing a worker node.
• Scheduler continuously queries the Apiserver at regular intervals to list the pods that have not been scheduled.
• Each pod object stored in Etcd has a property called 'nodeName' - it is the name of the worker node where the pod will deploy (nodeName assigned means the pod is scheduled).
• The scheduler is responsible for assigning the name of the worker node for each pod.

Controller-Manager

• Tries to maintain the actual state of the cluster as updated in the Etcd datastore.
• It performs garbage collection of pods, nodes, events, etc on the cluster.
• To handle multiple responsibilities different controllers are called.
• List of the few controllers
• NodeController
• NamespaceController
• EndpointsController
• ServiceaccountController

Kubelet

• The most important component of the worker node
• Interacts with the local Docker daemon on the worker node
• Kubelet is required to run on the host machine
• Kubelet refers to the configuration file ~/kubernetes/kubelet.conf
• Updates the 2 parameters in the config file:
• The endpoint of the Kube-apiserver component
• The local Docker daemon UNIX socket
• Kubelet is a bridge between Apiserver and the local container (Docker) daemon
• Kubelet runs a GET request at an interval of 20 seconds to the checklist of the pods created on Etcd.
• The kubelet performs garbage collection
• Verifies for unused images every five minutes
• Verifies for unused containers every minute

Kube-Proxy

• Handles all the networking related tasks on Kubernetes worker node for containers
• Enables access to the running pods to other pods or external applications
• The Proxy uses a feature called Service
• Services route traffic to Pods
• Maintains network rules on nodes to manage and allow network communication

Container Engine

• Kubernetes is a container management tool
• The Default Container engine is Docker
• Common container runtimes:
• Docker Engine
• Contained
• CRI-O
• Mirantis Container Runtime

Kubernetes Installation on Windows

Installation Steps:

1: Check if Virtualization is supported in your machine

$ systeminfo

2: Download/Install kubectl, minikube utility & Add it to the Local ENV PATH

https://kubernetes.io/docs/tasks/tools/install-kubectl-windows/

https://github.com/kubernetes/minikube/releases

• a. Download kubectl.exe file and place it in a dedicated folder (minikube folder).

  Set the environment variables

  Test the kubectl

  open cmd prompt (or power shell)

  type: kubectl and enter

• b. Download the file from github link share above

  minikube-windows-amd64.exe

  place the file in the folder where we have placed kubectl file (minikube folder).

3: Download/Install a Hypervisor | ORACLE VM BOX

https://www.virtualbox.org/wiki/Downloads

4: Start the Minikube (Specify the Driver)

syntax: $ minikube start --driver=driver_name

$ minikube start

or

$ minikube start --driver=virtualbox

5: To verify the Minikube installation

$ minikube status

minikube

type: Control Plane

host: Running

kubelet: Running

apiserver: Running

kubeconfig: Configured

6: Create & Expose a container in the Minikube Cluster

syntax: $ kubectl create deployment --image= [options]

> kubectl get pod

No resources found in default namespace.

> kubectl get deployment

No resources found in default namespace.

> kubectl create deployment test1-v1 --image=spark

deployment.apps/test1-v1 created

> kubectl get deployment

NAME READY UP-TO-DATE AVAILABLE AGE

test1-v1 0/1 1 0 28s

> kubectl get pod

NAME READY STATUS RESTARTS AGE

test1-v1-56f4d5f5b4-qm7qg 0/1 ErrImagePull 0 41s

> kubectl get service

NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE

kubernetes ClusterIP 10.96.0.1 443/TCP 2d17h

7: Test or Access the Container

$ minikube service test1-v1 --url

8: Cleanup

$ kubectl delete pods test1-v1

$ kubectl delete service test1-v1

$ minikube stop

$ minikube delete

Refer to a few kubectl commands

kubectl get nodes

kubectl get pod

kubectl get services

kubectl create deployment nginx-depl --image=nginx

kubectl get deployment

kubectl get replicaset

kubectl edit deployment nginx-depl

### debugging

kubectl logs {pod-name}

kubectl exec -it {pod-name} -- bin/bash

### create mongo deployment

kubectl create deployment mongo-depl --image=mongo

kubectl logs mongo-depl-{pod-name}

kubectl describe pod mongo-depl-{pod-name}

### delete deployment

kubectl delete deployment mongo-depl

kubectl delete deployment nginx-depl

### create or edit config file

vim nginx-deployment.yaml

kubectl apply -f nginx-deployment.yaml

kubectl get pod

kubectl get deployment

### delete with config

kubectl delete -f nginx-deployment.yaml

### Metrics

kubectl top

# The kubectl top command returns current CPU and memory usage for a cluster’s pods or nodes, or for a particular pod or node if specified.