# 2. K8s Architecture

### Node Processes

* Each Node has multiple Pods in it
* Worker Nodes do the actual work
* 3 processes must be installed on every Node
  1. **Container Runtime**
     * Docker or other technology
  2. **Kublet**
     * Interacts with both container and node
     * It starts the pod with a container inside
  3. **Kube proxy**
     * Forwards the requests between nodes

***

### Master Processes

* 4 processes must be installed on every master node which controls cluster state and worker nodes
  1. **API Server**
     * Could be UI, API, CLI, [Kubectl](https://notes.nomanaziz.me/devops/orchestration/kubernetes/3.-minikube-and-kubectl))
     * Acts as cluster gateway
     * Acts as gatekeeper for authentication
  2. **Scheduler**
     * API Server after validation of request hands over the request to scheduler
     * It just decides on which node new pod should be scheduled based on current resources of nodes
     * Kublet is the actual component which does the scheduling after getting request form scheduler
  3. **Controller Manager**
     * Detec cluster state changes like dying of podes
     * It makes a request to scheduler to restart the pod
  4. **etcd**
     * It is the cluster brain
     * cluster changes get stored in the key value store
     * application data is not stored in etcd
* On multiple master nodes
  * API server is load balanced
  * etcd forms distributed storage across all master nodes

<figure><img src="https://1920086362-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FDfv51K0WXLZdwTryHQZc%2Fuploads%2FSo7b7bx7ZVDgqjBpCAmU%2Fimage.png?alt=media&#x26;token=fdfef472-d083-44d7-90f8-260a34a288cb" alt=""><figcaption></figcaption></figure>


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