Kubernetes Architecture explained

Question 1

Each worker node has 3 processes that must be installed:

Answer 1

1) Container Runtime
2) Kubelet
3) Kube-proxy

These 3 processes are used to schedule and manage those Pods.

Question 2

Container runtime

Answer 2

Because application Pods have containers inside them, a container runtime must be installed on every Node.

Question 3

Kubelet is the process that

Answer 3

starts those Pods and the containers on the server

Question 4

Why does Kubelet have an interface with both: the container runtime and the server or the Node itself?

Answer 4

Kubelet needs to get resources, like CPU, RAM, and storage, from the worker node to create a Pod, and then it needs to talk to Docker to start a container inside the pod.

Question 5

Kube-proxy must be installed on every Node. This process is responsible for

Answer 5

forwarding requests from Services to Pods.

Question 6

Kube-proxy has built-in intelligent

Answer 6

forwarding logic that makes sure all communication is sent in the most efficient way

Question 7

When you as a user want to deploy a new application in a Kubernetes cluster, you interact with the

Answer 7

API server using a Kubernetes client

Question 8

The API server is like a cluster gateway, which receives the requests for

Answer 8

creating or updating components in the cluster, as well as queries about these components.

Question 9

The API server also acts as a gatekeeper to make sure that

Answer 9

only authenticated and authorized requests get through to the cluster

Question 10

After validating you, what does the API server do with your request?

Answer 10

It hands it over to the Scheduler to start the application Pod on one of the Worker Nodes.

Question 11

How does the scheduler intelligently decide which Worker Node the new Pod should be placed on?

Answer 11

1. 1. The Scheduler will look at your request and see how much resources the application that you want to schedule will need (CPU, RAM etc.)
2. Then it goes through the Worker Nodes to check the available resources on each one of them.
3. The Node with the most resources available or the least amount of load will be where the new pod is placed.

Question 12

The Controller Manager’s main job is detecting

Answer 12

state changes like the crashing of Pods for example.

Question 13

When the Controller Manager detects that a Pod has died it will make a

Answer 13

request to the Scheduler to redeploy that pod. The Scheduler may not put the pod back on the same Node it came from .

Question 14

etcd, is a

Answer 14

key value store of the cluster state

Question 15

etcd is often called the cluster brain, which means that

Answer 15

every change in the cluster, for example, when a new Pod gets scheduled, when a Pod dies, all of these changes get saved or updated into this key-value store of etcd.

Question 16

Scheduler, Controller manager, and Kubelet, work based on the data in

Answer 16

etcd as well as communicate with each other through etcd store.

Question 17

What is NOT stored in the etcd key-value store?

Answer 17

Application data.

For example, if you have a database running inside the cluster, the data will
be stored somewhere else. Etcd store only stores the cluster state
information.

Question 18

What are the three steps add a Master server to your Cluster?

Answer 18

1) Get a fresh new server
2) Install all the Master processes on it (API server, Scheduler, Controller Manager, etcd)
3) join it to the Kubernetes cluster using a Kubernetes command

Question 19

What are the three steps add Worker Nodes to your Cluster:

Answer 19

1) you get new servers
2) Install all the Worker Node processes (container runtime, Kubelet & KubeProxy)
3) join it to the cluster