40 Days Of Kubernetes (5/40)

Day 5/40

What is Kubernetes

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@piyushsachdeva
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We're going to look at Kubernetes architecture in depth.

1. Control Plane components.
2. Why it's needed.
3. How do they work?

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• Node is nothing but a virtual machine.

• Control Plane is a virtual machine that hosts many administrative components, like board in companies!

• Actual works are done by Worker Node.

• POD is the smallest deployable unit that can be managed by Kubernetes which can include one or multiple containers.

• API Server acts as the central management point of the entire Kubernetes cluster.

• Schedular is that it automatically decides how to distribute workloads across a cluster of servers.

• Controller Manager which handles all interactions with node controller, namespace controller, deployment controller, replication controller and so on, and make sure everything is up & running and monitored.

• etcd is a key-value datastore which stores the data required to manage clusters. Importantly.

• kubelet functions as an agent within nodes and is responsible for the running of pod cycles within each node.

• kube-proxy controls traffic routing and network connectivity for services within the cluster.

• kubectl is a command-line tool which command communicates with the kube-apiserver and sends orders to the control plane node.

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Work Flow

1. kubectl to api-server: Please create the pod
2. api-server validate and authenticate the user with etcd and notify the controller-manager.
3. controller-manager tells the api-server it's ok to have a POD
4. api-server write the request in etcd database.
5. etcd says to api-server yes it's done.
6. api-server says to scheduler to watch the new request.
7. schedular monitors and find out there's a pod creation request.
8. schedular says to api-server that I found a very special node for deploying the new pod.
9. api-server interacts with the kubelet of the selection node.
10. kubelet asks docker (or other alternative) to build the container with requeted image.
11. docker says to 'kubelet, hey deploy what I built.
12. kubelet run the pod and sends back the detail to api-server that the pod is deployed.
13. api-server update the related record in etcd database.
14. api-server sends the detail to kubectl and the user.