The Issue:

In the following sentence, there is a subject-verb agreement error.

If the Deployment is updated, the existing ReplicaSet that controls Pods whose labels match .spec.selector but whose template does not match .spec.template are scaled down.

The subject of the verb "are scaled down" is "the existing ReplicaSet", which is a singular noun. Therefore, the verb should be "is" instead of "are". The plural nouns "Pods" and "labels" appear between the subject and the verb, which likely caused the confusion.

Suggested Fix:

I suggest changing "are" to "is".

Incorrect:

...the existing ReplicaSet ... are scaled down.

Correct:

...the existing ReplicaSet ... is scaled down.

The fully corrected sentence would be:

If the Deployment is updated, the existing ReplicaSet that controls Pods whose labels match .spec.selector but whose template does not match .spec.template is scaled down.

This is a minor issue, but fixing it would improve the clarity and quality of the documentation.