A Kubernetes custom controller for facilitating ConfigMap rollouts. This is a proof-of-concept for kubernetes/kubernetes#31701.

Supposing you are running a local Kubernetes cluster via hack/local-cluster-up.sh, clone this repository under /tmp:

$ git clone https://github.com/kargakis/configmap-rollout /tmp/configmap-rollout $ cd /tmp/configmap-rollout

observer.yaml includes:

1. The observer Deployment that is running oc observe inside a Pod (see kubernetes/kubernetes#5164 for background) and uses a hostPort in order for the command to be able to contact the api server.

2. The script that runs every time a config map is created or updated (trigger.sh) mounted in the Deployment as a ConfigMap.

3. A kubeconfig that works ootb with local-cluster-up.sh mounted in the Deployment as a ConfigMap. If you need a different kubeconfig, delete the existing one and add yours.

Create the custom controller that will update Deployments on ConfigMap updates:

$ kubectl create -f observer.yaml configmap "kubeconfig" created configmap "trigger" created deployment "observer" created

Create a demo namespace and follow the example:

$ kubectl create -f example/example.yaml -n demo configmap "alpine" created deployment "alpine" created

At this point, you should have the following pods and config maps in the demo namespace:

$ kubectl get po -n demo NAME READY STATUS RESTARTS AGE alpine-928338976-59vhm 1/1 Running 0 17s

$ kubectl get cm -n demo NAME DATA AGE alpine 1 19s

You should be able to inspect our custom configuration in the alpine pod with the following command:

$ kubectl exec -n demo alpine-928338976-59vhm -i -t -- cat /etc/my-key Hello there!

Currently, there is no relation between the two resources other than the one (ConfigMap) being mounted in the other (Deployment). All you need in order to enable automatic rollouts in case of config map updates is to add a deployment.kubernetes.io/triggered-by: configmap/alpine annotation in the Deployment. This should be done by kubectl set trigger which is proposed in kubernetes/kubernetes#31701 - for now we will add it via kubectl annotate:

$ kubectl annotate deploy/alpine deployment.kubernetes.io/triggered-by=configmap/alpine -n demo deployment "alpine" annotated

Now update the alpine config map and change the message that will be echoed:

$ kubectl edit cm/alpine -n demo configmap "alpine" edited $ kubectl get cm/alpine -o jsonpath='{.data}' -n demo map[my-key:Updated!]

You should see a new rollout underway:

$ kubectl get po -n demo NAME READY STATUS RESTARTS AGE alpine-1077172096-zg3h2 0/1 ContainerCreating 0 3s alpine-928338976-59vhm 1/1 Terminating 0 4m

Inspect our configuration inside the new pod:

$ kubectl exec -n demo alpine-1077172096-zg3h2 -i -t -- cat /etc/my-key Updated!