If you are not familiar with the oc command, refer to OpenShift - Getting Started with the oc command.

Annotations and Labels are similar, but have important differences.

• Labels are used by OpenShift/Kubernetes, are limited by RFC 1123 to a maximum of 63 characters, and are used so that resource "a" can select resource "b" via the label.
• Annotations are NOT limited by RFC 1123 to a maximum of 63 characters, and contain metadata about a resource. Check out my article on the oc annotate command.
  • Some annotations are for humans (NOT OpenShift/Kuberneters), to displays some sort of metadata about a resource (e.g. app owner: John Doe)
  • Some annotations are used by OpenShift/Kubernetes (e.g. deployment.kubernetes.io/revision: "2")

Labels are metadata used so that resource "a" knows resource "b". For example, let’s say you have a deployment labeled my-deployment.

~]$ oc get deployment my-deployment -o yaml
metadata:
  labels:
    app: my-deployment
    app.kubernetes.io/component: my-deployment
    app.kubernetes.io/instance: my-deployment

And let's say replica set my-deployment-7d7f45d979 has selector matchLabels deployment: my-deployment. This is how the replica set knows that pods should be created for deployment "my-deployment".

~]$ oc get replicaset my-deployment-7d7f45d979 --output yaml
spec:
  selector:
    matchLabels:
      deployment: my-deployment

The pods will have a label so that the pods are for my-deployment.

~]$ oc get pod my-deployment-7d7f45d979-dm9g2 --output yaml
  labels:
    deployment: my-deployment

The service will have a selector specification that is used to determine the pod that the service should forward requests onto.

~]$ oc get service my-service --output yaml
spec:
  selector:
    deployment: my-deployment

The selector specification will tell the service to be labeled with my-deployment so that the service forwards requests onto the my-deployment pod.

~]$ oc get service my-service --output yaml
  labels:
    app: my-deployment
    app.kubernetes.io/component: my-deployment
    app.kubernetes.io/instance: my-deployment

The route will have the “to” specification to know which service and pod the request should be routed onto.

~]$ oc get route my-route --output yaml
spec:
  to:
    kind: Service
    name: my-deployment

The route will be labeled with my-deployment so that the route forwards requests onto the service that forwards requests onto the my-deployment pod.

~]$ oc get route my-route --output yaml
  labels:
    app: my-deployment
    app.kubernetes.io/component: my-deployment
    app.kubernetes.io/instance: my-deployment