node-role.kubernetes.io/control-plane is a new label introduced for the OpenShift Container Platform 4 - Control-Plane Node(s) as per https://kubernetes.io/docs/reference/labels-annotations-taints/#node-role-kubernetes-io-control-plane.

While it's automatically added for newly installed OpenShift Container Platform 4 - Cluster and newly created OpenShift Container Platform 4 - Control-Plane Node(s), it's not enforced or created for existing OpenShift Container Platform 4 - Cluster respectively existing OpenShift Container Platform 4 - Control-Plane Node(s).

This can be confusing for customers having long running OpenShift Container Platform 4 - Cluster and newly created OpenShift Container Platform 4 - Cluster as the default set of labels applied to the OpenShift Container Platform 4 - Control-Plane Node(s) are not the same.

It's therefore requested to document the reasoning behind this and to recommend to customers to manually add  node-role.kubernetes.io/control-plane to their existing OpenShift Container Platform 4 - Cluster to achieve consistency between newly created OpenShift Container Platform 4 - Cluster and long running OpenShift Container Platform 4 - Cluster.

OpenShift Container Platform 4.11, 4.12 and 4.13

Always

1. See problem description

Inconsistency that is per design but not documented that may raise question and support volume specifically when troubleshooting. 

Outline node-role.kubernetes.io difference between newly installed OpenShift Container Platform 4 - Cluster and long running OpenShift Container Platform 4 - Cluster and also provide details how long running OpenShift Container Platform 4 - Clusters can be label to have node-role.kubernetes.io/control-plane set as well and therefore comply with upstream kubernetes and newly installed OpenShift Container Platform 4 - Cluster

https://issues.redhat.com/browse/OCPNODE-709