CKA - Section 2: Core Concepts

Section 2: Core Concepts

12 / 41|3hr 2min

 

8. Core Concepts Section Introduction

9. Download Presentation Deck for this section

10. Cluster Architecture

 

Kubernetes Architecture

 

Master Node

(Manage, Plan, Schedule, Monitor, Nodes)

- ETCD Cluster 

- Kube-api Server

- Kube Controller Manager

- Kube-scheduler

 

Worker Nodes

(Host Application Containers)

- Kubelet

- Kube-proxy

- container Runtime Engine

 

11. ETCD For Beginner

ETCD is a distributed reliable key-value store that is Simple, Secure & Fast

 

12. ETCD in Kubernetes

 - Nodes / Pods / Configs / Secrets / Accounts / Roles / Bindings / Others

 

two types of k8s deployment 

1. scratch

2. kubeadm tool

- pods / kubectl .. commands

 

13. ETCD - Commands (Optional)

14. Kube-API Server

15.  Kube Controller Manager

- Watch status

 - Remediate Situation

16. Kube Scheduler

17. Kubelet 

18. Kube Proxy 

- service

- IP table rule

19. Recap - PODs

pod : container = 1 : 1

- kubectl 

> kubectl run nginx --image nginx

=> pod auto create -> deploy instance of nginx docekr iamge

> kubectl get pods

=> pod status check

20.  Pods with YAML

apiVersion

kind

metadata

- dictionary type

spec

single item list -> pod one container

- list/array

 

>  kubectl create -f pod-definitaion.yaml

=> pod 생성

 

> kubectl describe pod myapp-pod

=> pod에 대한 자세한 정보 확인하기

 

21. Demo - Pods with YAML

22. Practice Test Introduction

23. Demo: Accession Labs

24 ~ 26. kode kloud

kubectl run redis --image=redis123 --dry-run=client -o yaml > pod.yaml

kubectl apply -f pod.yaml

 

27. Recap - ReplicaSets

- High Availability

- Load Balancing & Scaling

o Replication Controller

apiVersions: v1

kind: ReplicationController

o Replica Set

apiVersions: apps/v1

kind: ReplicaSet

spec:

  selector:

    matchLabels:

        type:

-> difference: selector

 

labels and selectors

replica 3 -> 6

1. > kubectl replace -f replicaset-definitaion.yaml (yaml file edit replicas: 3->6)

2. > kubectl scale --replicas=6 -f replicaset-definition.yaml

3. > kubectl scale -replicas=6 replicaset myapp-replicaset (not update yaml file)

 

commands

> kubectl create -f replicaset-definition.yaml

> kubectl get replicaset

> kubectl delete replicaset myapp-replicaset

> kubectl replace -f replicaset-definition.yaml

> kubectl scale --replicas=5 replicaset "replicaset name"

 

28. Test - ReplicaSets

29. Test- ReplicaSets Solutions

 

30. Deployment

Rolling upgrade

Rollback

pod - replica Set - Deployment

> kubectl create -f deployment-definition.yaml

> kubectl get deployments

 

deployment -> auto create -> replica set

> kubectl get replicaset

> kubectl get pods

 

commands

> kubectl get all

 

31. tips

Create an NGINX Pod

kubectl run nginx --image=nginx



Generate POD Manifest YAML file (-o yaml). Don't create it(--dry-run)

kubectl run nginx --image=nginx --dry-run=client -o yaml



Create a deployment

kubectl create deployment --image=nginx nginx



Generate Deployment YAML file (-o yaml). Don't create it(--dry-run)

kubectl create deployment --image=nginx nginx --dry-run=client -o yaml



Generate Deployment YAML file (-o yaml). Don't create it(--dry-run) with 4 Replicas (--replicas=4)

kubectl create deployment --image=nginx nginx --dry-run=client -o yaml > nginx-deployment.yaml

Save it to a file, make necessary changes to the file (for example, adding more replicas) and then create the deployment.

 

> kubectl create deployment --image=["image name"] [deployment-name] --dry-run=client -o yaml

 

32. Practice Test - Deployments

33. Solution - Deployments

 

34. Namespaces

default -create automatically

Isolation, Policies, Resource limits

 

DNS 이용 방법

db-service [Service Name] . dev [Namespace] . svc [Service] . Cluster.local [Domain]

 

> kubectl get pods --namespace=kube-system

 

yaml

metadata:

    namespace: ...

 

Create Namespace

apiVersionn: v1 / kind: Namespace / metadata: name : dev

 

> kubectl create namespace dev

 

Switch

> kubectl config set-context $(kubectl config current-context) --namespace=dev

 

Get All Namespace

> kubectl get pods --all-namespaces

 

Resource Quota

 

35. Practice Test - Namespaces

36. Solution - Namespaces

 

37. Services - NodePort

service란 kubernetes 리소스 타입 중 하나로 각 pod로 트래픽을 포워딩 해주는 프록시 역할을 함.

이 때 selector 라는 것을 이용하여 트래픽을 전달받을 pod를 결정함.

 

backEnd - fronEnd connecting

 

- NodePort

단일 노드, 하나의 port를 수신하고 해당 port의 요청을 port로 전달하는 것

1) Target Port -- 2) Port (service aspect) 3) NodePort (External)

 

클러스터 IP로만 접근이 가능한 것이 아니라, 모든 노드의 IP와 프토를 통해서도 접근이 가능하게 됨.

 

Create Service

spec:

    type: Nodeport

    ports:

      - targetPort: 80

         port: 80
         nodePort: 30008

     selectors: (my app labels의 값 기재)

 

패킷의 흐름이 진행되는 이유는 kube-proxy라는 컴포넌트이기 때문임.

쿠버네티스는 리눅스 커널 기능 중 하나인 netfilter와 user space에 존재하는 인터페이스인 iptables라는 소프트웨어를 이용하여 패킷 흐름을 제어함.

 

netfilter란 Rule-based 패킷 처리 엔진이며, kernel space에 위치하여 모든 오고 가는 패킷의 생명주기를 관찰함.

그리고 규칙에 매칭되는 패킷을 발견하면 미리 정의된 action을 수행함.

 

iptables는 netfilter를 이용하여 chain rule이라는 규칙을 지정하여 패킷을 포워딩 하도록 네트워크를 설정함.

 

동일한 포트로 curl 시도하며 동일한 포트를 모든 노드에서 사용할 수 있음

- ClusterIP

- LoadBalancer

 

38. Services - Cluster IP

k8s cluster에 MSA(Micro Service Architecture) 기반 애플리케이션을 쉽고 효과적으로 배포할 수 있음

각 계층의 다양한 서비스 간의 통신에 영향을 주지 않음

 

디폴트 설정으로, 서비스에 클러스터 IP (내부 IP)를 할당한다.

쿠버네티스 클러스터 내에서는 이 서비스에 접근이 가능하지만, 클러스터 외부에서는 외부 IP를 할당 받지 못했기 때문에, 접근이 불가능함.

 

39. Services - Loadbalancer

보통 클라우드 벤터에서 제공하는 설정 방식으로, 외부 IP를 가지고 있는 로드 벨런서를 할당함.

외부 IP를 가지고 있기 때문에, 클러스터 외부에서 접근이 가능함.

 

조금 더 자세한 설명 참고

bcho.tistory.com/1262

쿠버네티스 #7 - 서비스 (Service)

 

40. Practice Test -  Services

41. Solution - Services (optional)

 

42. Imperative vs Declarative

Imperative 명령형 - 단계별 지침을 제공

create objects

update objects

yaml 을 처리할 필요가 없으므로 빠르게 실행됨

각 사용자마다 실행하는 명령어 환경이 다름

자격증 시험을 위해서는 명령형 사용하는 것 연습해야함

 

Declarative 선언형 - 최종 목적지만 선언, 단계별 지침 제공하지 않음 / 우리의 요구사항 선언

> kubectl apply -f nginx.yaml

개체가 이미 존재하거나 업데이트를 적용할 수 없다는 오류가 실제로 발생하지 않음

 

Exam Tips

Create Objects

> kubectl apply -f nginx.yaml

> kubectl run --image=nginx nginx

> kubectl create deployment --image=nginx nginx

> kubectl expose deployment nginx --port 80

 

Update Objects

> kubectl apply -f nginx.yaml

> kubectl edit deployment nginx

> kubectl scale deployment nginx --replicase=5

> kubectl set image deployment nginx nginx=nginx:1.18

 

 

43. Certification Tips - Imperative Commands with Kubectl

 

While you would be working mostly the declarative way - using definition files, imperative commands can help in getting one time tasks done quickly, as well as generate a definition template easily.

This would help save a considerable amount of time during your exams.

Before we begin, familiarize with the two options that can come in handy while working with the below commands:

 

--dry-run: By default as soon as the command is run, the resource will be created. If you simply want to test your command, use the --dry-run=client option. This will not create the resource, instead, tell you whether the resource can be created and if your command is right.

 

-o yaml: This will output the resource definition in YAML format on the screen.

 

Use the above two in combination to generate a resource definition file quickly, that you can then modify and create resources as required, instead of creating the files from scratch.

 

- POD

Create an NGINX Pod

kubectl run nginx --image=nginx

 

Generate POD Manifest YAML file (-o yaml). Don't create it(--dry-run)

kubectl run nginx --image=nginx  --dry-run=client -o yaml

- Deployment

Create a deployment

kubectl create deployment --image=nginx nginx

 

Generate Deployment YAML file (-o yaml). Don't create it(--dry-run)

kubectl create deployment --image=nginx nginx --dry-run -o yaml

 

Generate Deployment with 4 Replicas

kubectl create deployment nginx --image=nginx --replicas=4

 

You can also scale a deployment using the kubectl scale command.

kubectl scale deployment nginx --replicas=4

 

Another way to do this is to save the YAML definition to a file.

kubectl create deployment nginx --image=nginx--dry-run=client -o yaml > nginx-deployment.yaml

You can then update the YAML file with the replicas or any other field before creating the deployment.

 

- Service

Create a Service named redis-service of type ClusterIP to expose pod redis on port 6379

kubectl expose pod redis --port=6379 --name redis-service --dry-run=client -o yaml

(This will automatically use the pod's labels as selectors)

Or

kubectl create service clusterip redis --tcp=6379:6379 --dry-run=client -o yaml

  (This will not use the pods labels as selectors, instead it will assume selectors as app=redis. You cannot pass in selectors as an option. So it does not work very well if your pod has a different label set. So generate the file and modify the selectors before creating the service)

 

Create a Service named nginx of type NodePort to expose pod nginx's port 80 on port 30080 on the nodes:

kubectl expose pod nginx --port=80 --name nginx-service --type=NodePort --dry-run=client -o yaml

(This will automatically use the pod's labels as selectors, but you cannot specify the node port. You have to generate a definition file and then add the node port in manually before creating the service with the pod.)

Or

kubectl create service nodeport nginx --tcp=80:80 --node-port=30080 --dry-run=client -o yaml

(This will not use the pods labels as selectors)

Both the above commands have their own challenges. While one of it cannot accept a selector the other cannot accept a node port. I would recommend going with the `kubectl expose` command. If you need to specify a node port, generate a definition file using the same command and manually input the nodeport before creating the service.

 

Reference:

https://kubernetes.io/docs/reference/kubectl/conventions/

 

44. Practice Test - Imperative Commands

45. Solution - Imperative Commands (optional)

 

46. Kubectl Apply Command

Local file (.yaml)-> Last applied Configuration (.json) -> Kubernetes

> kubectl apply -f nginx.yaml

 

47, 48. End

 

 

Udemy 한글자막 javascript code

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Kubectl 자동완성 명령어

 

echo "source <(kubectl completion bash)" >> ~/.bashrc
alias k=kubectl
complete -F __start_kubectl k

 

github.com/ahmetb/kubernetes-network-policy-recipes/blob/master/04-deny-traffic-from-other-namespaces.md

ahmetb/kubernetes-network-policy-recipes