(My) Educational example of how to create a Kubernetes operator/controller in Rust using the Kube client.

This repo creates a controller for a CRD (Custom Resource Definition) called Echo that will:

• create a deployment with the hashicorp/http-echo image, using the number of replicas and text (as --text={text}) specified;
• and create a NodePort service to expose this deployment externally to the cluster.
• adds a finalizers to control the CRD deletion.

Echo example:

apiVersion: test.com/v1
kind: Echo
metadata:
  name: test-echo
  namespace: default
spec:
  replicas: 2
  text: Hello world

This example was deeply inspired by the projects:

• https://github.com/Pscheidl/rust-kubernetes-operator-example
• https://github.com/kube-rs/controller-rs/blob/main/src/controller.rs

and in the examples found in the kube repo.

Ps: this repository is educational only and does not necessarily reflect standards that should be used in production.

In this repository I am using the terms Kubernetes operator and Kubernetes controller interchangeably - which is not conceptually correct - but simplifies our discussion.

Technically, there is no difference between a typical controller and an operator. Often the difference referred to is the operational knowledge that is included in the operator. As a result, a controller which spins up a pod when a custom resource is created and the pod gets destroyed afterwards can be described as a simple controller. If the controller has additional operational knowledge like how to upgrade or remediate from errors, it is an operator. – https://github.com/cncf/tag-app-delivery/blob/eece8f7307f2970f46f100f51932db106db46968/operator-wg/whitepaper/Operator-WhitePaper_v1-0.md

• Install Rust
• Install kubectl
• Install some local (lightweight) Kubernetes distribution and create a local cluster. I’m using Kind.
• Run kubectl apply -f echoes.test.com.yaml to create the Echo cdr definition ().
• Run cargo run to start the Echo controller.
• Run kubectl apply -f echo-test.yaml to create a test-echo Echo crd example.
• Run kubectl get all to see the pods, deployment, services being created.
• Run curl <node-ip>:/<NodePort> to get the text specified inside echo-test.yaml.
• Change the test-echo definition, like the number of replicas, then:
  • Run kubectl apply -f echo-test.yaml, kubectl get all to watch the changes happening, and curl again.

• [ ] Add tests.
• [ ] Review/Add OwnerReference chain.