Maintaining Idempotency in Complex Kubebuilder Projects

[mingregister]

Kubebuilder requires the implementation of the Reconcile function to be idempotent, but as the project becomes increasingly complex, I find it very difficult to maintain its idempotency. Do you have any suggestions? Are there any production-ready projects based on Kubebuilder that I can refer to?

[mattwelke]

Can you be more specific about the challenges you've run into? Maybe some examples?

[camilamacedo86]

Hi @mingregister

The Golden Rule of maintaining idempotency in the Reconcile function reflects how Kubernetes itself operates. When we extend the Kubernetes API, we’re essentially extending its behaviour. Idempotency is fundamental to ensuring the predictable and reliable operation of the Kubernetes control plane.

This principle ensures that even if the Reconcile function is triggered multiple times—due to retries, updates, or other events—it consistently drives the system toward the desired state without unintended side effects.

The whole point of Kubernetes' design is that we declare the desired state, and a loop (controller/reconciler) continuously works to achieve and maintain that state. That is what happens when, for example, we create a Deployment or Pod.

If you haven't checked yet, I recommend you check the following resources. I hope that helps you.

1. Read the "15-Minute Kubebuilder Getting Started Guide":
   Kubebuilder Getting Started

2. Deep Dive into GVKs (Group-Version-Kind):
   GVKs Tutorial

3. Give a look at: https://kubernetes.io/docs/concepts/extend-kubernetes/operator/

4. Run and Explore the Scaffold:

   • Initialize a new project and create an API:

     kubebuilder init
     kubebuilder create api \
       --group example.com \
       --version v1alpha1 \
       --kind Memcached \
       --image=memcached:1.6.26-alpine3.19 \
       --image-container-command="memcached,--memory-limit=64,-o,modern,-v" \
       --image-container-port="11211" \
       --run-as-user="1001" \
       --plugins="deploy-image/v1-alpha" \
       --make=false

   • Spend some time (1 hour recommended) analyzing the scaffold, focusing on:
     • Controller logic
     • Test files

If you have anything specifically that you are facing a challenge with, please share it to see if we can help you.