The in-use-protector is an external controller that monitors objects' useeReference field and blocks deletion of the used objects while they are in-use. This controller is intended to be used with other controllers that maintain the useeReference fields by detecting the user-usee relationships between specific objects with their domain specific knowledges. An example of such controllers is secret-protection controller.

Most of the codes in this repo are modified and copied from garbagecollector. The useeReference field is currently implemented as k8s.io/useereference annotation, just for a quick prototype. However, it should be implemented as object's metadata fields in the same way that ownerReference is implemented.

This project is still pre-alpha. This is just a prototype for discussion purpose.

make container-in-use-protector

(Above container image needs to be available before below command, such as by running kind load docker-image.)

kubectl create -f examples/kubernetes/rbac-in-use-protector.yaml
kubectl create -f examples/kubernetes/setup-in-use-protector.yaml

kubectl delete -f examples/kubernetes/setup-in-use-protector.yaml
kubectl delete -f examples/kubernetes/rbac-in-use-protector.yaml

While this controller is deployed, k8s.io/in-use-protection finalizers are added to resources that were referenced via useeReference, these finalizers are needed to be manually deleted after the controller is undeployed.

For example, to remove finalizers from test-secret secret, run below comand.

kubectl patch secret test-secret -p '{"metadata":{"finalizers":[]}}' --type=merge

1. Create a Secret and check that there is no finalizers added

kubectl create secret generic test-secret --from-literal='username=my-app' --from-literal='password=39528$vdg7Jb'
kubectl get secret test-secret -o jsonpath='{.metadata.finalizers}{"\n"}'

2. Create a Pod that has useeReference to the secret

uid=$(kubectl get secret test-secret -o jsonpath='{.metadata.uid}')

cat << EOF | kubectl create -f -
apiVersion: v1
kind: Pod
metadata:
  name: user-pod
  annotations:
    k8s.io/useereference: '[{"apiVersion": "core/v1", "kind": "Secret", "name": "test-secret", "uid": "$uid"}]'
spec:
  containers:
  - name: nginx
    image: nginx:1.14.2
EOF

As the above example shows, in-use protector doesn't care if the resource is actually using the resource that useeReference defines. It is completely up to users or controllers to ensure that references reflect the real relationships.

3. Check that the k8s.io/useereference finalizer is added to test-secret by the in-use protector and deletionTimestamp is empty.

kubectl get secret test-secret -o jsonpath='{.metadata.finalizers}{"\n"}'

[k8s.io/in-use-protection] is shown.

kubectl get secret test-secret -o jsonpath='{.metadata.deletionTimestamp}{"\n"}'

Nothing is shown.

4. Try to delete the secret while it is in-use and check that it remains with the finalizer and non-empty deletionTimestamp

kubectl delete secret test-secret --wait=false
kubectl get secret test-secret -o jsonpath='{.metadata.finalizers}{"\n"}'

[k8s.io/in-use-protection] is shown.

kubectl get secret test-secret -o jsonpath='{.metadata.deletionTimestamp}{"\n"}'

Something like 2021-07-22T17:53:00Z is shown.

5. Delete the user-pod and confirm that the secret is also deleted.

kubectl delete pod user-pod

pod "user-pod" deleted is shown.

kubectl get secret test-secret -o jsonpath='{.metadata.finalizers}{"\n"}'

Error from server (NotFound): secrets "test-secret" not found is shown.