Kubernetes Learning Part II - Understanding of Kubernetes Architecture and Hands-on Lab Setup

Saravanan Gnanaguru - Apr 18 '22 - - Dev Community

Kubernetes Learning Series - Part II

Table of contents

Introduction

  • In this article we will discuss the Kubernetes architecture and how to set up the lab environment to run the Kubernetes commands.
  • This blog is part of the Kubernetes Learning series
  • In the previous blog, we discussed about architecture decision that provides when to choose k8s for our application deployments

Kubernetes High Level Architecture

  • Let us now discuss Kubernetes Architecture and components
  • Kubernetes has two major building blocks,
    1. Kubernetes Control Plane (or Master Node as called previously)
    2. Nodes (or Worker Node as called previously)

Control Plane

Kubernetes Control Plane has four major components,
1. Kube API Server : This component exposes Kubernetes API and acts as a front end of k8s control plane. kubectl is used to interact with API servers.
2. ETCD : Secure key-value store
3. Kube Scheduler : Watches newly created Pod with and selects node for those pods to run
4. Controller Manager : This component manages the four controller processes of Kubernetes

  • Node Controller
  • Job Controller
  • End-point Controller
  • Service account & Token Controller

Kubernetes Architecture

Node

A node consists of,
1. Kubelet : An agent that runs on each node in the cluster. It makes sure that containers are running in a Pod.
2. Kube-proxy : kube-proxy is a network proxy that runs on each node in your cluster, implementing part of the Kubernetes Service concept.
3. Container Runtime : The container runtime is the software that is responsible for running containers.
Kubernetes supports several container runtimes: Docker, containerd, CRI-O, and any implementation of the Kubernetes CRI (Container Runtime Interface).
4. Pods : Pods are the smallest deploy-able units of computing that we can create and manage in Kubernetes.
A Pod (as in a pod of whales or pea pod) is a group of one or more containers, with shared storage and network resources, and a specification for how to run the containers.

Refer Kubernetes Component Documentation for more details.

Kubernetes Tools

  • There are various tools available to getting started with Kubernetes by doing the setup in User Workstation
  • Tools that provide local cluster,
    • Minikube
    • Kind
  • Tools to interact with Kubernetes
    • Kubectl
    • Kubeadm

As part of learning and to practice Kubernetes, we will pick-up minikube installation steps.

Refer documentation for more details

What is Minikube

  • minikube is a CLI tool that lets you run Kubernetes cluster locally on any workstation.
  • It runs a single-node Kubernetes cluster on our personal computer (including Windows, macOS and Linux OS) so we can try out Kubernetes learning, and for any daily development work.
  • Minikube cluster packs both the master and worker components for us to get started with managing the container.
  • Below diagram depicts the minikube single node cluster, Minikube Cluster

Version information

While writing this article, Kubernetes version is 1.23.0 and minikube version is 1.25.2

Minikube Installation Steps

  • In order to getting started with minikube, we need to install below components in our workstation

    • Install curl command
    • Install docker
    • Install minikube
    • Install kubectl

  • I have carried out the steps in Ubuntu 21.04 based operating system

  • Refer minikube documentation for installation steps for other operating systems

Install curl 

sudo apt update
sudo apt install curl -y
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Install docker 

# Update the apt package index, and install the latest version of Docker Engine and containerd, 
# or go to the next step to install a specific version:
sudo apt update -y
sudo apt install -y docker-ce docker-ce-cli containerd.io

# Add current user to 'docker' user group to invoke minikube (otherwise, the .sock permission denied error will occur)
sudo usermod -aG docker $USER
newgrp docker

# Verify that Docker Engine is installed correctly by running the hello-world image.
sudo docker run hello-world
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Install Minikube 

cd /tmp
curl -LO https://storage.googleapis.com/minikube/releases/latest/minikube_latest_amd64.deb
sudo dpkg -i minikube_latest_amd64.deb
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Minikube Run

  • Start minikube cluster and provide docker as the container runtime engine 
$ minikube start --driver=docker
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  • If we want to run minikube with specific version of kubernetes, it can done using the option --kubernetes-version, 
minikube start --kubernetes-version=v1.11.10
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Sample Output of minikube start and status

  • It will show up the below output in console 
😄  minikube v1.22.0 on Ubuntu 21.04
✨  Using the docker driver based on user configuration
👍  Starting control plane node minikube in cluster minikube
🚜  Pulling base image ...
💾  Downloading Kubernetes v1.21.2 preload ...
    > preloaded-images-k8s-v11-v1...: 502.14 MiB / 502.14 MiB  100.00% 7.75 MiB
    > gcr.io/k8s-minikube/kicbase...: 361.09 MiB / 361.09 MiB  100.00% 5.08 MiB
🔥  Creating docker container (CPUs=2, Memory=3900MB) ...
🐳  Preparing Kubernetes v1.21.2 on Docker 20.10.7 ...
    ▪ Generating certificates and keys ...
    ▪ Booting up control plane ...
    ▪ Configuring RBAC rules ...
🔎  Verifying Kubernetes components...
    ▪ Using image gcr.io/k8s-minikube/storage-provisioner:v5
🌟  Enabled addons: storage-provisioner, default-storageclass
💡  kubectl not found. If you need it, try: 'minikube kubectl -- get pods -A'
🏄  Done! kubectl is now configured to use "minikube" cluster and "default" namespace by default
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  • Minikube status command, 
$ minikube status
minikube
type: Control Plane
host: Running
kubelet: Running
apiserver: Running
kubeconfig: Configured
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Install Kubectl

  • minikube comes with the desired version of kubectl so, if we don't install kubectl explicitly, then we can invoke kubectl commands as below, 
minikube kubectl -- <expected kubectl command>
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  • Otherwise, follow the kubectl installation doc to install it
  • If we installed kubectl, then we can invoke kubectl commands as below, 
kubectl <expected kubectl command>
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Kubectl installation steps for Ubuntu,
Run below commands to install kubectl

sudo snap install kubectl --classic
kubectl version
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Verify and Run Minikube Cluster

  • We can use kubectl commands to verify the installed cluster and other details.
  • We can use it to access our new cluster created using minikube 
kubectl get po -A
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or

minikube kubectl -- get po -A
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  • It shows the below output, which shows the deployed single node cluster created using minikube
  • Please note components from control plane and worker node available as part of minikube deployment 
$ kubectl get po -A
NAMESPACE              NAME                                         READY   STATUS    RESTARTS   AGE
kube-system            coredns-558bd4d5db-4tncm                     1/1     Running   5          9d
kube-system            etcd-minikube                                1/1     Running   5          9d
kube-system            kube-apiserver-minikube                      1/1     Running   5          9d
kube-system            kube-controller-manager-minikube             1/1     Running   5          9d
kube-system            kube-proxy-wtzn9                             1/1     Running   5          9d
kube-system            kube-scheduler-minikube                      1/1     Running   5          9d
kube-system            storage-provisioner                          1/1     Running   10         9d
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  • Then, we can try performing the creation of new k8s deployments, 
minikube kubectl -- create deployment hello-minikube --image=k8s.gcr.io/echoserver:1.4
minikube kubectl -- expose deployment hello-minikube --type=NodePort --port=8080

minikube kubectl -- get services hello-minikube
minikube service hello-minikube
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  • The entire Minikube cluster can be visualised using the below command, 
minikube dashboard
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Conclusion

  • We have covered kubernetes architecture understanding and gone through the setup of lab for k8s hands-on
  • Try out and start hands-on with Kubernetes and let me know your feedback
  • This article was previously published on my dev community personal profile, re-publishing for the benefit of a wider audience.
  • Hope this article is helpful to people getting started with kubernetes.

Thanks for reading!

Heads up for Next Blog

We will further explore topics like deployment of pods and services in next blog

Follow me and share your thoughts,

Bibliography

Kubernetes official documentation
Minikube documentation

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