create Replicaset with separate pods in Kubernetes

Question

I want to create a ReplicaSet with separate pods.

Pods

apiVersion: v1
kind: Pod
metadata:
  name: user-pod
  labels:
    app: user-pod
spec:
  containers:
    - name: user-container
      image: kia9372/store-user

Replicaset

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: user-replicaset
  labels:
    app: user-replicaset
spec:
  replicas: 3
  selector:
    matchLabels:
      app: user-pod

but when i execute the following command, it throws the foloowing error:

kubectl create -f user-replicaset.yml 
 
>error: error validating "user-replicaset.yml": 
error validating data: ValidationError(ReplicaSet.spec.selector): 
unknown field "app" in io.k8s.apimachinery.pkg.apis.meta.v1.LabelSelector; 
if you choose to ignore these errors, turn validation off with --validate=false

What's the problem? how can I solve this?

Answer 1

matchlabels is missing. Also your pod definition does not define a matching label.

Have a look at the docs for a proper setup: https://kubernetes.io/docs/concepts/workloads/controllers/replicaset/

Answer 2

Did you try adding that label also in Replicaset:

apiVersion: apps/v1
kind: ReplicaSet    
metadata:
  labels:
    app: user-replicaset
    app: user-pod

This example uses that label in both labels

Answer 3

you can't create replicaset without spec.template.spec.containers field. as this one is by default required to create replica-set in k8s. so you must need to add template field. and you can actually do what you want, just use your pod as here in template spec. template is the actual pod spec with which you are going to create your replica-set's pods.

this one is going to do the exact thing you are asking for:

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: user-replicaset
  labels:
    app: user-replicaset
spec:
  replicas: 3
  selector:
    matchLabels:
      app: user-pod
  template:
    metadata:
      labels:
        app: user-pod
    spec:
      containers:
      - name: user-container
        image: kia9372/store-user