How to correctly change the value of a ConfigMap so that the service sees it?

To change the value of a ConfigMap and have the service see these changes, you need to:

1. Update the ConfigMap using the command kubectl apply -f configmap.yaml or kubectl edit configmap <name>.
2. If the service uses the ConfigMap as environment variables, then to apply the changes, you need to restart the pods, as environment variables are read only at container startup.
3. If the ConfigMap is mounted as a volume, then changes in the files inside the volume are usually visible immediately, but the application should be able to detect changes and reload the configuration without a restart.

Example of restarting a pod:

kubectl rollout restart deployment/<deployment-name>

Thus, to have the service see the ConfigMap updates, it usually requires restarting the pod or deployment.