Today I was going through some documentation and discussions about matchLabels statement that is a part of a Deployment (or other objects) in Kubernetes. Example below:
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-deployment
labels:
app: nginx
spec:
replicas: 3
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:1.7.9
ports:
- containerPort: 80In some discussions, I saw that depending on the version of the API it could be optional or mandatory to use this selector.
Ref:
https://github.com/helm/charts/issues/7680
What is the purpose of a kubernetes deployment pod selector?
But I can't see any official documentation where it is stated explicitly if the usage of this selector was mandatory or not for a specific version of a Kubernetes API. Do you know of any official documentation where it is stated whether or not it is mandatory to use matchLabels selector?
I have checked these links out but I did not bump into an official statement: https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.10/#deploymentspec-v1beta2-apps
https://kubernetes.io/docs/concepts/workloads/controllers/deployment/
kubectl explain deploy.spec.selector --api-version=apps/v1
Label selector for pods. Existing ReplicaSets whose pods are selected by this will be the ones affected by this deployment. It must match the pod template's labels.
Selector *metav1.LabelSelector `json:"selector" protobuf:"bytes,2,opt,name=selector"`The lack of +optional above this line tells you it's mandatory. It matches up with the error message you'll get if you try to make a deployment without one.
cat <<EOF | kubectl apply -f -
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx
spec:
replicas: 1
template:
spec:
containers:
- image: nginx
imagePullPolicy: Always
name: nginx
dnsPolicy: ClusterFirst
restartPolicy: Always
EOFerror: error validating "STDIN": in io.k8s.api.apps.v1.DeploymentSpec; if you choose to ignore these errors, turn validation off with --validate=false. error validating data: ValidationError(Deployment.spec): missing required field "selector"
type LabelSelector struct {
// matchLabels is a map of {key,value} pairs. A single {key,value} in the matchLabels
// map is equivalent to an element of matchExpressions, whose key field is "key", the
// operator is "In", and the values array contains only "value". The requirements are ANDed.
// +optional
MatchLabels map[string]string `json:"matchLabels,omitempty" protobuf:"bytes,1,rep,name=matchLabels"`
// matchExpressions is a list of label selector requirements. The requirements are ANDed.
// +optional
MatchExpressions []LabelSelectorRequirement `json:"matchExpressions,omitempty" protobuf:"bytes,2,rep,name=matchExpressions"`
}