How to patch a ConfigMap in Kubernetes

Question

Kubernetes ships with a ConfigMap called coredns that lets you specify DNS settings. I want to modify or patch a small piece of this configuration by adding:

apiVersion: v1
kind: ConfigMap
data:
  upstreamNameservers: |
    ["1.1.1.1", "1.0.0.1"]

I know I can use kubectrl edit to edit the coredns ConfigMap is there some way I can take the above file containing only the settings I want to insert or update and have it merged on top of or patched over the existing ConfigMap?

The reason for this is that I want my deployment to be repeatable using CI/CD. So, even if I ran my Helm chart on a brand new Kubernetes cluster, the settings above would be applied.

Answer 1

As ConfigMaps are used to mount configuration files to Pod, it seems like this is what you are looking for. ConfigMaps inside of containers will update automatically if the underlying ConfigMap or Secret is modified.

You can specify configMap location:

configMapVolume(mountPath: '/etc/mount3', configMapName: 'my-config'),

Update:

Ok, I guess this does not solve your issue. Other thing that comes to my mind is kubectl create configmap with a pipe to kubectl replace So the whole command would look like this:

kubectl create configmap NAME --from-file file.name -o yaml --dry-run | kubectl replace -f -

Note that this replaces whole file, so just replace should work too.

Answer 2

you can edit it using vi as follows:

    kubectl edit cm -n kube-system coredns 

or you can export it to apply any changes using kubectl get cm -n kube-system -o yaml --export then use kubectl apply -f fileName.yaml to apply your changes

Answer 3

This will apply the same patch to that single field:

kubectl patch configmap/coredns \
  -n kube-system \
  --type merge \
  -p '{"data":{"upstreamNameservers":"[\"1.1.1.1\", \"1.0.0.1\"]"}}'

Answer 4

you should try something like this:

kubectl get cm some-config -o yaml | run 'sed' commands to make updates | kubectl create cm some-config -o yaml --dry-run | kubectl apply -f -