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What is a Cluster in Kubernetes

Kubernetes coordinates a highly available cluster of computers that are connected to work as a single unit. 

  • The abstractions in Kubernetes allow you to deploy containerized applications to a cluster without tying them specifically to individual machines. 
  • To make use of this new model of deployment, applications need to be packaged in a way that decouples them from individual hosts: they need to be containerized. Containerized applications are more flexible and available than in past deployment models, where applications were installed directly onto specific machines as packages deeply integrated into the host. 
  • Kubernetes automates the distribution and scheduling of application containers across a cluster in a more efficient way.

A Kubernetes cluster consists of two types of resources:

    1. The Control Plane coordinates/manages the cluster

    • The Control Plane coordinates all activities in your cluster, such as 
      • scheduling applications,
      • maintaining applications' desired state e.g. replicas etc
      • scaling applications 
      • and rolling out new updates
    2.  A Node is a VM or a physical computer that serves as a worker machine in a Kubernetes          cluster  
    • Each node has a Kubelet, which is an agent for managing the node and communicating with the Kubernetes control plane.
    • Kubernetes cluster that handles production traffic should have a minimum of three nodes because if one node goes down, both an etcd member and a control plane instance are lost, and redundancy is compromised. You can mitigate this risk by adding more control plane nodes.
  • When you deploy applications on Kubernetes, you tell the control plane to start the application containers. The control plane schedules the containers to run on the cluster's nodes. Node-level components, such as the kubelet, communicate with the control plane using the Kubernetes API, which the control plane exposes. End users can also use the Kubernetes API directly to interact with the cluster.
  • A Kubernetes cluster can be deployed on either physical or virtual machines.


Once the application instances are created, a Kubernetes Deployment controller continuously monitors those instances. If the Node hosting an instance goes down or is deleted, the Deployment controller replaces the instance with an instance on another Node in the cluster. This provides a self-healing mechanism to address machine failure or maintenance.




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