label's key names are not uniform between monitor and pd/tidb/tikv about tidb-operator HOT 2 CLOSED

According to k8s documentation on label key:

Labels are key/value pairs. Valid label keys have two segments: an optional prefix and name, separated by a slash (/). The name segment is required and must be 63 characters or less, beginning and ending with an alphanumeric character ([a-z0-9A-Z]) with dashes (-), underscores (_), dots (.), and alphanumerics between. The prefix is optional. If specified, the prefix must be a DNS subdomain: a series of DNS labels separated by dots (.), not longer than 253 characters in total, followed by a slash (/). If the prefix is omitted, the label Key is presumed to be private to the user. Automated system components (e.g. kube-scheduler, kube-controller-manager, kube-apiserver, kubectl, or other third-party automation) which add labels to end-user objects must specify a prefix. The kubernetes.io/ prefix is reserved for Kubernetes core components.

We should use the long names: an prefix and name, separated by a slash (/).

from tidb-operator.

I agree that label keys should contain a domain prefix. So it can be selected by label selector without conflict with other apps.

But for annotations, it's usually used internally and can't be queried by keys. So shorter keys are fine enough and we can source the annotations in our scripts without errors.

As for multiple words in label key, we should follow Kubernetes convention using a dash(-) to separate them. But for annotations, because we use annotations key-value pair in scripts via source we should use underscore(_) to avoid sourcing errors.

from tidb-operator.