Question

A developer is writing a Deployment manifest. They set spec.selector.matchLabels to {app: web, tier: frontend}, but under spec.template.metadata.labels they only put {app: web}. When they run kubectl apply, the command is rejected. What is the reason for this error?

Accepted Answer

The Deployment's selector must match the labels defined in the Pod template; a selector label with no corresponding template label is invalid.

Answer

A Deployment selector can only contain a single label key, so specifying two keys is not allowed.

Answer

Pod template labels must be a strict superset of the selector, so the template needs at least three labels to be valid.

Answer

The selector and template labels are unrelated, so the error must be caused by an invalid apiVersion in the manifest.