Kubernetes – Components / Cluster architecture – simplifying concepts – detailed article

Hi All,

Greetings for the day!!!

Lets continue Kubernetes series.

We are discussing Kubernetes. In previous few articles we discussed

• What is Kubernetes ? – https://knowledge-junction.in/2021/09/03/kubernetes-introduction-starting-point-for-beginners-helps-to-prepare-the-interview/
• Setting up local environment for Kubernetes – https://knowledge-junction.in/2021/09/11/kubernetes-simplifying-setting-up-local-environment-creating-kubernetes-cluster-locally-helps-in-interview-preparation-kubernetes-for-beginners/
• Yaml file guide / reference – https://knowledge-junction.in/2021/09/04/complete-guide-to-yaml/
• Kubernetes – Setting up kubernetes cluster for development on Windows 10 box using minikube – https://knowledge-junction.in/2022/05/06/kubernetes-setting-up-kubernetes-cluster-for-development-on-windows-10-box-using-minikube/
• Kubernetes – POD – https://knowledge-junction.in/2022/05/05/kubernetes-pod/
• Kubernetes – Objects – simplifying concepts – https://knowledge-junction.in/2022/05/28/kubernetes-objects-simplifying-concepts/

Today we will discuss Kubernetes architecture and Kubernetes cluster

Kubernetes cluster is collection of Nodes – either physical or virtual network where Kubernetes (Kubernetes components) installed

Nodes details

• Machine either physical or virtual where Kuebernatics is installed
• Worker machine where containers are launched by Kubernatics
• Each node is managed by control plane
• There are two types of Nodes
  • Master Node
  • Worker Node
• Node Name – naming convention / best practices
  • Node name must be unique.
  • Name identifies the Node
  • Node name must be a valid DNS subdomain name
    • contain no more than 253 characters
    • contain only lowercase alphanumeric characters, ‘-‘ or ‘.’
    • start with an alphanumeric character
    • end with an alphanumeric character

Kubernetes Cluster Components

Master Node / Control Plane

• Master node / control plane includes the components which controls cluster, its data state and its configuration
• Each worker node managed by control plane and contains necessary components / services to successfully run the PODs
• Control Plane Components:
  • API Server
    • Component of Kubernetes control plane that exposes the Kubernetes API
    • The API server services REST operations through which all other components interact
    • The API server is accessible from outside the cluster
    • Client (example – user executes the Kubectl command) authenticates via API server
  • etcd service
    • Distributed, reliable key value store to store all data to manage cluster
    • Store all the details on all nodes
    • responsible for implementing logs
    • Data in etcd is accessible only by Kubernetes API Server
  • Controllers
    • Kube controller manager
      • Component which runs controller processes
      • Few types of controllers are following which controller runs
        • Node Controller
          • Notices and responds when node goes down
          • Example –
            • When running in a cloud environment and whenever a node is unhealthy, the node controller asks the cloud provider if the VM for that node is still available.
            • If not, the node controller deletes the node from its list of nodes.
        • Job Controller
        • Replication controller – Controls number of replicas in a POD
        • EndPoints Controller – Populates end point objects like services and pods
        • Service account and Token Controllers
    • Cloud controller manager
      • This component is responsible for managing controller processes with dependencies on respective cloud provider
  • Schedulers
    • Responsible for distributing work across containers across multiple nodes
    • This means, responsible for scheduling Pods on respective worker nodes – Check for the PODs which are newly created and not assigned to any node – assigns the node to run successfully

Worker Nodes

• Every Kubernetes cluster at least have one worker node
• Worker node hosts the PODs – means our containerised application runs on worker node
• Worker node components
  • Container Runtime
    • Container runtime engine (its a software) is responsible for running containers
    • Docker is one of the example of container runtime
  • Kubelet
    • This component runs on each node
    • This component makes sure that containers are running in a Pod
    • This component makes sure containers running in a Pods are in healthy state
  • Kube-Proxy
    • Proxy service runs on each node
    • This component implements part of Kubernetes Service concept
    • Exposes services on the external world
    • This component makes sure request is forwarded to correct container / POD in a cluster

Few Node CMDLETs – Here, I am using minikube

• Get all nodes

kubectl get nodes

Output will be

• To get all labels of node

kubectl get nodes --show-labels

Output will be

• To view the node status and other details – describe attribute to Kubectl cmdlet is used as

kubectl describe node <insert-node-name-here>

Thanks for reading!!! Please feel free to discuss in case any questions / suggestions / thoughts !!!

HAVE A GREAT TIME AHEAD !!! LIFE IS BEAUTIFUL 🙂