kustomize's docs provides a nice one-liner that compares two different overlays...
diff \
<(kustomize build $OVERLAYS/staging) \
<(kustomize build $OVERLAYS/production)is there a way to do the same but against what is running within a specific kubernetes namespace and that of a defined overlay on disk?
more specifically, knowing what an kubectl apply -k . would do without actually doing it? using --dry-run just says spits out a list of the objects rather than a real diff.
Try this kustomize command, currently in alpha:
KUSTOMIZE_ENABLE_ALPHA_COMMANDS=true kustomize resources diff -k your/kustomize/overlayI'm not sure if this is what you are looking for, but in Kubernetes you have kubectl diff.
It's nicely explained on APIServer dry-run and kubectl diff.
You can use option -k, --kustomize which does:
Process the kustomization directory. This flag can't be used together with -f or -R.
Or maybe something similar to one-liner to set context for specific namespace:
$ kubectl config set-context staging --user=cluster-admin --namespace=staging
$ kubectl config set-context prod --user=cluster-admin --namespace=prodOnce you have context setup you could use them maybe in a following way:
kubectl config use-context staging; cat patched_k8s.yaml | kubectl config use-context prod; kubectl diff -f -This is just an example which I did not tested.