SteakfulSet controller 🥩

In Kubernetes, we are talking a lot about StatefulSets. But what about SteakfulSets? Sounds delicious to you? Read on...

Description

This repository implements a small and simple Kubernetes controller that reconciles on the custom resource SteakfulSet and creates Steaks - another custom resource - out of it. It is intended to give a you an idea about what it takes to implement your own Kubernetes operator - something you might come across doing at some point in time.

This repository is heavily based on Kubebuilder and the Kubebuilder book. In fact, Kubebuilder has been used to create the skeleton of this repository, to provide all the generators and to design the CRD layout.

File layout

The custom resources

The custom resources SteakfulSet and Steak are defined in Go source code within the files inside the api/v1alpha folder. Inside the Go source files, we use some Kubebuilder decorators to describe some spefic of the custom resources. Then, the following command will invoke Kubebuilder's generator to create the custom resource definition files:

make manifests

The resulting CRDs can be found in the config/crd directory.

The controller

The controller consists of only two files: the controller is set up and initialized in main.go. A quick overview about what happens in here is given in chapter 1.7.1 of the Kubebuilder book - in fact, main.go only contains generated code.

The real fun happens in controllers/steakfulset_controller.go. In here, the reconcilation logic for SteakfulSets is implemented. Have a look at the comments of the Reconcile() method to get an idea what happens.

Getting Started

You’ll need a Kubernetes cluster to run against. You can use KIND to get a local cluster for testing, or run against a remote cluster. Note: Your controller will automatically use the current context in your kubeconfig file (i.e. whatever cluster kubectl cluster-info shows).

Helm Chart

To install the SteakfulSet controller into your cluster with the help of Helm, simply look into the charts directory. Install it with:

kubectl create ns steakfulset-controller
helm install -n steakfulset-controller bbq charts/steakfulset-controller

To fry your first Steaks, just kubectl apply -f config/samples/food_v1alpha1_steakfulset.yaml.

Running manually on the cluster

1. Install the CRDs into the cluster:

   make install

2. Build and push your image to the location specified by IMG:

   make docker-build docker-push IMG=<some-registry>/steakfulset-controller:tag

   Note: If you are building this on arm64 (read 🍎 Apple Silicon) and your Kubernetes cluster is running with amd64 machines, you need to set the environment variable BUILDPLATFORM to linux/amd64 before running this command.

3. Deploy the controller to the cluster with the image specified by IMG:

   make deploy IMG=<some-registry>/steakfulset-controller:tag

Uninstall CRDs

To delete the CRDs from the cluster:

make uninstall

Undeploy controller

UnDeploy the controller from the cluster:

make undeploy

More on Kubernetes controllers?

More information can be found via the Kubebuilder Documentation