ReplicaSet

Problem

If a pod is running a web application and the pod goes down, then users won't be able to access the data.

Somone would need to log in and fix the problem, but this takes time.

ReplicaSet

If a pod crashes, it will create a new pod automatically with a health check.

A ReplicaSet can be used to scale the number of pods.

Example YAML

vim sampleReplicaSet.yaml:

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: frontend
  labels:
    app: guestbook
    tier: frontend
spec:
  # modify replicas according to your case
  replicas: 3
  selector:
    matchLabels:
      tier: frontend
  template:
    metadata:
      labels:
        tier: frontend
    spec:
      containers:
        - name: php-redis
          image: gcr.io/google_samples/gb-frontend:v3

Commands

create replica:

kubectl create -f sampleReplicaSet.yaml

update replica:

kubectl apply -f sampleReplicaSet.yaml

get replica:

kubectl get rs

get pods:

kubectl get pod

scale replicas:

# not recomended in production
kubectl scale --replicas=1 rs/frontend
# frontend = replica name

edit live config:

# not recomended in production
kubectl edit rs frontend

delete replica:

kubectl delete rs frontend