[Udemy] ReplicaSet

kubernetes/udemy

[Udemy] ReplicaSet

bbiyak2da 2025. 2. 12. 17:30

ReplicaSet

ReplicaSet은 지정된 수의 Pod 복제본이 항상 실행되도록 보장하는 컨트롤러
Pod가 실패하거나 삭제되면, ReplicaSet은 자동으로 새로운 Pod를 생성하여 원하는 상태를 유지
ReplicaSet을 사용하여 여러 개의 파드 복제본을 관리할 때, 서비스(Service)를 활용하여 이러한 파드에 대한 로드 밸런싱을 제공

ReplicaSet 생성

# replicaset-demo.yml 파일 작성

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: my-helloworld-rs
  labels:
    app: my-helloworld
spec:
  replicas: 6
  selector:
    matchLabels:
      app: my-helloworld
  template:
    metadata:
      labels:
        app: my-helloworld
    spec:
      containers:
      - name: my-helloworld-app
        image: stacksimplify/kube-helloworld:1.0.0

# replicaset 생성

kubectl create -f replicaset-demo.yml
replicaset.apps/my-helloworld-rs created

# replicaset 확인

kubectl get rs        
NAME               DESIRED   CURRENT   READY   AGE
my-helloworld-rs   6         6         6       2m4s

kubectl describe rs
Name:         my-helloworld-rs
Namespace:    default
Selector:     app=my-helloworld
Labels:       app=my-helloworld
Annotations:  <none>
Replicas:     6 current / 6 desired
Pods Status:  6 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
  Labels:  app=my-helloworld
  Containers:
   my-helloworld-app:
    Image:        stacksimplify/kube-helloworld:1.0.0
    Port:         <none>
    Host Port:    <none>
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Events:
  Type    Reason            Age    From                   Message
  ----    ------            ----   ----                   -------
  Normal  SuccessfulCreate  3m41s  replicaset-controller  Created pod: my-helloworld-rs-kkklm
  Normal  SuccessfulCreate  3m41s  replicaset-controller  Created pod: my-helloworld-rs-tmbcr
  Normal  SuccessfulCreate  3m41s  replicaset-controller  Created pod: my-helloworld-rs-r55cx
  Normal  SuccessfulCreate  3m41s  replicaset-controller  Created pod: my-helloworld-rs-28v29
  Normal  SuccessfulCreate  3m41s  replicaset-controller  Created pod: my-helloworld-rs-wlx6b
  Normal  SuccessfulCreate  3m41s  replicaset-controller  Created pod: my-helloworld-rs-zzznq

replicaset을 6으로 지정하여, pod 6개를 확인할 수 있다

# pod 확인

kubectl get pods
NAME                     READY   STATUS    RESTARTS   AGE
my-helloworld-rs-28v29   1/1     Running   0          13m
my-helloworld-rs-kkklm   1/1     Running   0          13m
my-helloworld-rs-r55cx   1/1     Running   0          13m
my-helloworld-rs-tmbcr   1/1     Running   0          13m
my-helloworld-rs-wlx6b   1/1     Running   0          13m
my-helloworld-rs-zzznq   1/1     Running   0          13m

ReplicaSet을 Service를 통해 노출

# replicaset을 Service를 통해 노출

# Expose ReplicaSet as a Service
kubectl expose rs <ReplicaSet-Name>  --type=LoadBalancer --port=80 --target-port=8080 --name=<Service-Name-To-Be-Created>
kubectl expose rs my-helloworld-rs  --type=LoadBalancer --port=80 --target-port=8080 --name=my-helloworld-rs-service

# Get Service Info
kubectl get service
kubectl get svc

# Service의 External IP를 통해, Pod 내 애플리케이션 접근

http://<External-IP-from-get-service-output>/hello

replicaset을 통해 6개의 pod가 생성되었고,

expose 명령어를 통해 Load Balancer(service)를 생성하여서

service의 외부 IP를 통해 접근 시, pod가 로드밸런싱 되는 것을 확인 가능

ReplicaSet의 High Availability

# pod 삭제

kubectl get pods
---
NAME                     READY   STATUS    RESTARTS   AGE
my-helloworld-rs-28v29   1/1     Running   0          17m
my-helloworld-rs-kkklm   1/1     Running   0          17m
my-helloworld-rs-r55cx   1/1     Running   0          17m
my-helloworld-rs-tmbcr   1/1     Running   0          17m
my-helloworld-rs-wlx6b   1/1     Running   0          17m
my-helloworld-rs-zzznq   1/1     Running   0          17m

여기서 한 개의 pod를 삭제해보자

kubectl delete pod my-helloworld-rs-28v29
pod "my-helloworld-rs-28v29" deleted

# pod 확인

kubectl get pods
---
NAME                     READY   STATUS    RESTARTS   AGE
my-helloworld-rs-kkklm   1/1     Running   0          17m
my-helloworld-rs-q7gpp   1/1     Running   0          6s
my-helloworld-rs-r55cx   1/1     Running   0          17m
my-helloworld-rs-tmbcr   1/1     Running   0          17m
my-helloworld-rs-wlx6b   1/1     Running   0          17m
my-helloworld-rs-zzznq   1/1     Running   0          17m
PS C:\Users\serahp\azure-aks-kubernetes-masterclass\03-Kubernetes-Fun

28v29가 삭제 되고, q7gpp라는 새로운 pod가 생성되어 파드 수가 6개로 유지되는 것을 확인 가능

이는 replicaset의 High Availability 기능 때문이다.

ReplicaSet의 Scalability

# replicaset-demo.yaml 파일 수정

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: my-helloworld-rs
  labels:
    app: my-helloworld
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-helloworld
  template:
    metadata:
      labels:
        app: my-helloworld
    spec:
      containers:
      - name: my-helloworld-app
        image: stacksimplify/kube-helloworld:1.0.0

replicas를 6 -> 3으로 수정해보자

# replicaset 수정

kubectl replace -f replicaset-demo.yml 
replicaset.apps/my-helloworld-rs replaced

# replicaset 및 pod 확인

kubectl get rs
NAME               DESIRED   CURRENT   READY   AGE
my-helloworld-rs   3         3         3       28m

kubectl get pods -o wide
NAME                     READY   STATUS    RESTARTS   AGE   IP             NODE                                NOMINATED NODE   READINESS GATES
my-helloworld-rs-r55cx   1/1     Running   0          26m   10.224.0.70    aks-agentpool-29221675-vmss000000   <none>           <none>
my-helloworld-rs-tmbcr   1/1     Running   0          26m   10.224.0.149   aks-agentpool-29221675-vmss000001   <none>           <none>
my-helloworld-rs-wlx6b   1/1     Running   0          26m   10.224.0.95    aks-agentpool-29221675-vmss000000   <none>           <none>

pod 수가 3으로 자동적으로 조정된 것을 볼 수 있다.

# clean

kubectl get rs   
NAME               DESIRED   CURRENT   READY   AGE
my-helloworld-rs   3         3         3       28m

kubectl delete rs my-helloworld-rs
replicaset.apps "my-helloworld-rs" delete

[참고 영상]

Udemy - Azure Kubernetes Service with Azure DevOps and Terraform

섹션 4 : Kubernetes Fundamentals with kubectl - Imperative Approach

25. Step-12 : Introduction ot Kubernetes Deployments

[참고 문서]

https://github.com/stacksimplify/azure-aks-kubernetes-masterclass/tree/master/03-Kubernetes-Fundamentals-with-kubectl/03-02-ReplicaSets-with-kubectl