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.

Sire

Answer 1

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\"]"}}'

Earthen

What if I wanted to add this into a Helm chart somehow? – Sire

Hi @MuhammadRehanSaeed, Helm is for deploying and managing 'artifacts' or self contained systems. I don't think it's appropriate to use Helm to modify system configs. – Angeliqueangelis

This answer is correct; but, there are more ways to patch a resource. See: kubernetes.io/docs/tasks/run-application/… – Angeliqueangelis

This is invaluable for sooo many use cases. It's a pity this cannot be found on the docs. Thank you! – Eydie

@ Jordan Liggitt this way doesn't work if the whole config under data field is in form of embedded json string. – Gutta

I am not sure if this will also work for file-like keys. This works perfectly for property-like keys. – Jerrodjerrol

@Gutta for that case I prefer to use jq. E.g. kubectl get configmap/coredns -n kube-system -o json | jq '.data.Corefile += "localnet:53 {\n errors\n cache 30\n forward . '"$(minikube ip)"'\n}\n"' | kubectl apply -f - – Haemolysin

Answer 2

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 - 

Embolectomy

The question asks how to do this in a CI/CD environment where manually editing some files is not possible. – Sire

@MuhammadRehanSaeed This answer does not involve manually editing files. – Tallent

This is a more general answer which is correct and you should be able to run this script in your CI/CD pipeline – Jerrodjerrol

Answer 3

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

Splasher

The question asks how to do this in a CI/CD environment where manually editing some files is not possible. – Sire

Answer 4

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.

Piefer