How do I remove a specific block from the value of a config map?

Question

I have a config map that looks like this:

kubectl describe configmap example-config --namespace kube-system
Name:         example-config
Namespace:    kube-system
Labels:       <none>
Annotations:  <none>

Data
====
mapRoles:
----
- rolearn: arn:aws:iam::0123456789012:role/user-role-1
  username: system:node:{{EC2PrivateDNSName}}
  groups:
  - system:bootstrappers
  - system:nodes
- rolearn: arn:aws:iam::0123456789012:role/user-role-2
  username: system:node:{{EC2PrivateDNSName}}
  groups:
  - system:bootstrappers
  - system:nodes

I want to remove user-role-2 from the configmap. I think I need to use kubectl patch with a "remove" operation. What is the syntax to remove a section from a config map?

Here is an example command I can use to append to the config map:

kubectl patch -n=kube-system cm/aws-auth --patch "{\"data\":{\"mapRoles\": \"- rolearn: "arn:aws:iam::0123456789012:role/user-role-3" \n  username: system:node:{{EC2PrivateDNSName}}\n  groups:\n  - system:bootstrappers\n  - system:nodes\n\"}}" 

Answer 1

According to kubernetes official docs: https://kubernetes.io/docs/tasks/manage-kubernetes-objects/update-api-object-kubectl-patch/

There is not such syntax in kubectl patch to remove a section from an api object like a config map.

Here is an example command I can use to append to the config map:

kubectl patch -n=kube-system cm/aws-auth --patch "{\"data\":{\"mapRoles\": \"- rolearn: "arn:aws:iam::0123456789012:role/user-role-3" \n username: system:node:{{EC2PrivateDNSName}}\n groups:\n - system:bootstrappers\n - system:nodes\n\"}}"

The command above is used to replace the whole data field in configmap. So you can simply use it to patch update with the data you want:

kubectl patch -n=kube-system cm/example-config --patch '{"data":{"mapRoles": "- rolearn: arn:aws:iam::0123456789012:role/user-role-1\n  username: system:node:{{EC2PrivateDNSName}}\n  groups:\n  - system:bootstrappers\
n  - system:nodes"}}'

Answer 2

I think the simplest way is like this:

kubectl get configmaps foo -o yaml > foo.yaml

Now edit foo.yaml the way you want

Then apply your new config:

kubectl apply -f foo.yaml