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Kubernetes - Architecture

 What is Kubernetes:

    Kubernetes is an open source container orchestration system for automating application deployment,     scaling, self-healing, rolling update and roll back.

 

Architecture Diagram:



Master Node / Control Plane components:

  1.     Kube API server
  2.     Scheduler
  3.     Controller Manager
  4.     etcd store


1. Kube API Server:

  •  API server acts as a front-end to kubernetes cluster & exposes the kubernetes cluster API.
  •  API server talks to worker nodes.
  •  API server validates and configures data for the api objects which includes pods, service replica-controllers, deployments etc.
  •  Once request is validated, it stores the cluster data under etcd store.


2. Schedulers:

  •  Scheduler assigns pods to nodes
  •  Scheduler determines which nodes are free and can take a new load. 
  •  Scheduler also checks for constraints before placing the load on any nodes.


3. etcd  store:

  •  Kubernetes uses etcd ro store all cluster data - configuration data, its state and metadata.
  •  Since Kubernetes is a distributed system- it needs a distributed data store like etcd.
  •  etcd manages a lot of the tricky problems in running a distributed database like race conditions.
  •  It also stores the actual state of the system and the desired state of the system in etcd.
  •  It then uses etcd's watch functionality to monitor changes to either of these two things. If they    diverge, Kubernetes makes changes to reconcile the actual state and the desired state.
  •  kubectl get pod --> reads from etcd store data.
  •  Any change you make via kubectl create will write an entry in etcd.


4. Controller Manager:

  •  A kube-controller manager is a daemon which regulates the state of the system. 
  •  A controller is a non terminating loop that watches the state of the cluster via kube api server and makes changes attempting to move the current state to desired state.
  •  example: replica-controllers , end point controllers etc.

Node Components:

  1. Kubelet
  2. Run time environemnt
  3. Kube-proxy

1. Kubelet:

  • Kubelet is a node agent that runs on every node in a kubernetes cluster. 
  • It can register the node with the kube api server using hostname or any other logic.
  • Kubelet takes the podspecs and ensures containers described in podspec or healthy.
  • kubelet doesn't monitor containers which doesn't create via kubernetes.

2. Run time environment:

  • All Nodes should be installed with docker or containerd (container runtime environment)

3. Kube Proxy:

  • Kube proxy is a network proxy which maintains network rules on nodes.


Happy Learning😀
Thank you

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