ReplicaSet Finder

A toy Kubernetes controller that labels K8s Deployments with the names of their corresponding ReplicaSets.

Features

This simple controller is built using the controller-runtime library and operates on Kubernetes Deployments. When the controller is running, it "reconciles" Kubernetes Deployment resources (in all namespaces) using the custom reconciliation logic.

This controller works as an add-on to the native Deployment controller (part of kubernetes-controller-manager) running in the K8s Control Plane. It does not . The only 'reconcilliation' this controller provides is to look for the ReplicaSet owned by a Deployment resource and, after it finds it, to add a label to the Deployment with the name of the found ReplicaSet.

Source Code (Go Packages)

• (package main)cmd/main.go: creates a new manager, a controller that operates on Deployment resources, reconciles them with the implemented reconciler, and starts the created manager.
• (package controller)internal/controller/controller.go: implements reconcilliation logic for the Deployment resource, i.e., finding owned ReplicaSet and adding its name as a label to the reconciled Deployment resource.

The Ginkgo test suite in the controller package is designed from the perspective of local development. They can only run against a locally running K8s cluster with kubeconfig in the default location. Just run ginkgo run -v in the internal/controller directory to run the test suite (pre-requisite: ginkgo installed locally).

Usage

Local

Pre-requisites

• Go v1.24.0
• Access to K8s cluster (looks for the config file in .kube/config)

Steps The controller can run locally on your machine with access to a local or remote Kubernetes cluster. Just build the controller using go build cmd/main.go and run the generated executable.

K8s cluster

Pre-requisites

• Kubernetes cluster (tested using Kubernetes v1.32.0 on minikube)

Steps

1. Build the image:

docker build -t <NAME>:<TAG> .

The image name and tag used in the provided K8s manifests is rs-finder:latest. Don't forget to customize the manifests accordingly if you choose a different name/tag while building your image.

2. Load the built image to your local cluster, e.g., in a minikube cluster. Refer to Loading an Image Into Your Cluster if you are using kind.

minikube load image <NAME>:<TAG>

3. Create required Kubernetes resources (RBAC, namespace, controller deployment) in the manifests directory. The controller should be running as a deployment in the rsfinder-system namespace.
4. Deployments running in the cluster (across all namespaces) should now have a new label owned-replica-set: <RS_NAME> as part of their metadata.

Contributions

Feel free to use this basic controller as your starting journey into building custom Kubernetes controllers using the controller-runtime library. If you think of enhancing this basic controller further, don't hesitate to create a PR.