I have a deployment yaml file that looks like this:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-kubernetes
spec:
  replicas: 1
  selector:
    matchLabels:
      app: hello-kubernetes
  template:
    metadata:
      labels:
        app: hello-kubernetes
    spec:
      setHostnameAsFQDN: true
      hostname: hello
      subdomain: world
      containers:
      - name: hello-kubernetes
        image: redis 

However, I am getting this error:

$ kubectl apply -f dep.yaml  

error: error validating "dep.yaml": error validating data: ValidationError(Deployment.spec.template.spec): unknown field "setHostnameAsFQDN" in io.k8s.api.core.v1.PodSpec; if you choose to ignore these errors, turn validation off with --validate=false

My kubectl version:

$ kubectl version --client
Client Version: version.Info{Major:"1", Minor:"20", GitVersion:"v1.20.0", GitCommit:"af46c47ce925f4c4ad5cc8d1fca46c7b77d13b38", GitTreeState:"clean", BuildDate:"2020-12-08T17:59:43Z", GoVersion:"go1.15.5", Compiler:"gc", Platform:"darwin/amd64"}

After specifying --validate=falsee, hostname and hostname -f still return different values.

I believe I missunderstood something. Doc says that setHostnameAsFQDN will be available from kubernetes v1.20