Update k8s ConfigMap or Secret without deleting the existing one

For future reference, kubectl replace is now a very handy way to achieve this

kubectl replace -f some_spec.yaml Let you update a complete configMap (or other objects)

See doc and examples directly here

Copy/pasted from the help:

# Replace a pod using the data in pod.json.
kubectl replace -f ./pod.json

# Replace a pod based on the JSON passed into stdin.
cat pod.json | kubectl replace -f -

# Update a single-container pod's image version (tag) to v4
kubectl get pod mypod -o yaml | sed 's/\(image: myimage\):.*$/\1:v4/' | kubectl replace -f -

# Force replace, delete and then re-create the resource
kubectl replace --force -f ./pod.json

For small changes in configMap, use edit

kubectl edit configmap <cfg-name>

This will open configMap in vi editor. Make the changes and save it.

You can get YAML from the kubectl create configmap command and pipe it to kubectl apply, like this:

kubectl create configmap foo --from-file foo.properties -o yaml --dry-run | kubectl apply -f -