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Prasanth Bupd
Prasanth Bupd

Posted on • Originally published at bupd.hashnode.dev

Geek's Guide to Kubernetes Image Credential Provider Plugins: No Bloat

#kubernetes #devops #architecture #docker

I spent more than 8 hours wrestling with Kubernetes image credential provider plugins before finally stumbling upon the real solution. If you think this is as simple as dropping a config into Kind or Minikube think again. It doesn’t work that way, and I’d rather save you the wasted time I went through.

This guide comes from someone who considers a debugger “bloat.” If you share that mindset, you’ll feel right at home.

In this blog, I will walk you step by step through setting up a Kubernetes image credential provider plugin in a Kind cluster. We’ll manually configure the Kubelet to use your custom credential provider plugin. no shortcuts, no bloat, just the essentials.

Step 1

🔹Create your Cluster.

I am going for a basic three-node cluster to work with. Use the following configuration to spin it up. This setup includes one control-plane node and two worker nodes. feel free to add more configs if you want.

# this config file contains all config fields with comments
kind: Cluster
apiVersion: kind.x-k8s.io/v1alpha4
nodes:
# the control plane node config
- role: control-plane
# the workers
- role: worker
- role: worker
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Step 2

🔹Copy the Credential Provider Plugin Binary and Config to all the nodes.

You can also use a daemonset to do this in production. but I have gone with simple docker cp. Because we are still in the development stage of the credential-provider-plugin. I have my credentilal-plugin and config in a directory

❯ ls -la credential-provider-plugin
total 22524
drwxr-xr-x  2 bupd bupd     4096 Aug 30 06:21 .
drwxr-xr-x 22 bupd bupd     4096 Aug 30 06:23 ..
-rw-r--r--  1 bupd bupd      495 Aug 30 06:21 config.yml                     # config
-rwxr-xr-x  1 bupd bupd 12034738 Aug 30 06:18 credential-provider-echo-token # binary
-rwxr-xr-x  1 bupd bupd 10988078 Aug 28 17:25 credential-provider-echo-token-old
-rw-r--r--  1 bupd bupd      993 Aug 28 17:24 go.mod
-rw-r--r--  1 bupd bupd     8341 Aug 28 17:24 go.sum
-rw-r--r--  1 bupd bupd     3088 Aug 30 06:18 main.go
-rw-r--r--  1 bupd bupd     1734 Aug 28 17:25 README.md

# copy the entire folder into k8s nodes
docker cp ./credential-provider-plugin kind-control-plane:/etc/kubernetes/credential-providers
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Step 3

🔹Modify the Kubelet Configuration

The real fun begins now. The Kubelet's configuration on a kind cluster is managed by a file called kubeadm-flags.env. We need to pull this file from the control-plane node, modify it, and push it back.

It will be located in /var/lib/kubelet/kubeadm-flags.env *link

Now copy the file from k8s node to host

docker cp kind-control-plane:/var/lib/kubelet/kubeadm-flags.env ./kubeadm-flags-kind.env
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Edit the file to include the credential provider flags

  • --image-credential-provider-bin-dir: The directory where our plugin binary resides.
  • --image-credential-provider-config: The path to the configuration file for the plugin. Note: Don't forget to separately quote the values. Seriously, I've seen two hours vanish because of this.

Before:

KUBELET_KUBEADM_ARGS="--node-ip=172.18.0.3 --node-labels= --pod-infra-container-image=registry.k8s.io/pause:3.10.1 --provider-id=kind://docker/kind/kind-control-plane"
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After:

do remember to add the ’ to the values.

KUBELET_KUBEADM_ARGS="--node-ip=172.18.0.3 --node-labels= --pod-infra-container-image=registry.k8s.io/pause:3.10.1 --provider-id=kind://docker/kind/kind-control-plane --image-credential-provider-bin-dir='/etc/kubernetes/credential-providers' --image-credential-provider-config='/etc/kubernetes/credential-providers/config.yml'"
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Copy the modified file back to the control plane

docker cp ./kubeadm-flags-kind.env kind-control-plane:/var/lib/kubelet/kubeadm-flags.env
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Step 4

🔹Restart the kubelet

Get into the control-plane node

docker exec -it kind-control-plane sh
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once you are inside the node execute the below command

Run the reload and restart commands

systemctl daemon-reload && systemctl restart kubelet
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Step 5

The most reliable way to verify if your plugin is working is to embed a webhook into it. This allows all inputs and outputs to be sent to a webhook endpoint, giving you a straightforward way to monitor the plugin’s execution. While it may feel a bit hacky, i love it. implementation here

Another way to test the plugin is by pulling an image that requires the default static credentials configured in your plugin. If the plugin is working correctly, the pod should start successfully with the image, confirming that the pull operation uses the expected credentials.

You can try this by applying the example pod.yaml file:

kubectl apply -f pod.yaml
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Once the pod starts, you’ll be able to confirm that the hardcoded credentials from the credential-provider-plugin is being used as intended.

If you have other ideas or approaches for monitoring plugin execution, feel free to share them in the comments!

📚 References

This is a finicky process, and things can go wrong. Here are some resources that I found invaluable while navigating this.

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