patch a configmap from file or with json - kubernetes

Question

I want to edit a configmap from aws-auth during a vagrant deployment to give my vagrant user access to the EKS cluster. I need to add a snippet into the existing aws-auth configmap. How do i do this programmatically?
If you do a kubectl edit -n kube-system configmap/aws-auth you get
apiVersion: v1
data:
mapRoles: |
- groups:
- system:bootstrappers
- system:nodes
rolearn: arn:aws:iam::123:role/nodegroup-abc123
username: system:node:{{EC2PrivateDNSName}}
kind: ConfigMap
metadata:
creationTimestamp: "2019-05-30T03:00:18Z"
name: aws-auth
namespace: kube-system
resourceVersion: "19055217"
selfLink: /api/v1/namespaces/kube-system/configmaps/aws-auth
uid: 0000-0000-0000
i need to enter this bit in there somehow.
mapUsers: |
- userarn: arn:aws:iam::123:user/sergeant-poopie-pants
username: sergeant-poopie-pants
groups:
- system:masters
I've tried to do a cat <<EOF > {file} EOF then patch from file. But that option doesn't exist in patch only in the create context.
I also found this: How to patch a ConfigMap in Kubernetes
but it didn't seem to work. or perhaps i didn't really understand the proposed solutions.

Answer 1

There are a few ways to automate things. The direct way would be kubectl get configmap -o yaml ... > cm.yml && patch ... < cm.yml > cm2.yml && kubectl apply -f cm2.yml or something like that. You might want to use a script that parses and modifies the YAML data rather than a literal patch to make it less brittle. You could also do something like EDITOR="myeditscript" kubectl edit configmap ... but that's more clever that I would want to do.

Answer 2

First, note that the mapRoles and mapUsers are actually treated as a string, even though it is structured data (yaml).
While this problem is solvable by jsonpatch, it is much easier using jq and kubectl apply like this:
kubectl get cm aws-auth -o json \
| jq --arg add "`cat add.yaml`" '.data.mapUsers = $add' \
| kubectl apply -f -
Where add.yaml is something like this (notice the lack of extra indentation):
- userarn: arn:aws:iam::123:user/sergeant-poopie-pants
username: sergeant-poopie-pants
groups:
- system:masters
See also https://docs.aws.amazon.com/eks/latest/userguide/add-user-role.html for more information.

Answer 3

Here is a kubectl patch one-liner for patching the aws-auth configmap:
kubectl patch configmap -n kube-system aws-auth -p '{"data":{"mapUsers":"[{\"userarn\": \"arn:aws:iam::0000000000000:user/john\", \"username\": \"john\", \"groups\": [\"system:masters\"]}]"}}'