I am trying to do some research on replicaSet for my learning purpose. I was able to create a replicaSet successfully with matchLabels. To test the matchExpression selector, I created a pod first then a new replica set to test if the replica set will be able to check the labels from the running pods. But this failed with error. Here is what I did so far.

1. Created a pod first with a specific label. Pod runs successfully.
2. Create a replicaSet with matchExpressions matching the value with the label specified in the pod.

After the second step I get error. Below are the YAML files and the error. Can you help me understand the issue here ?

Here is the pod-definition.yaml

apiVersion: v1
kind: Pod
metadata:
  name: nginx-app
  labels:
    tier: frontend1

spec:
  containers:
  - name: nginx-c
    image: nginx

Here is the replicaset-definition.yaml

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: replicaset-2
spec:
  replicas: 2
  selector:
    matchExpressions:
      - {key: tier, operator: In, values: [frontend1]}
  template:
    metadata:
      labels:
        tier: nginx
    spec:
      containers:
      - name: nginx
        image: nginx

Error while creating replica set:

master $ kubectl create -f /root/replicaset-definition.yaml

The ReplicaSet "replicaset-2" is invalid: spec.template.metadata.labels: Invalid value: map[string]string{"tier":"nginx"}: selector does not match template labels