PodSet Operator

Objective of this Operator/Controller is demonstrate ReplicaSet kind of resource implementation using Kubernetes controller pattern. Another objective of this repo. is to show how to build the controller from scratch and what challenges a developer could face. So that a developer could understand the beauty KuberBuilder or Operator SDK frameworks

PodSet resource

Once user applies the PodSet (kubectl apply -f podset.yaml) resource, controller could spin up number of pods mentioned as per replicas filed.

e.g. User want to spin up 3 pod

apiVersion: demo.k8s.io/v1alpha1
kind: PodSet
metadata:
  name: three-podset
spec:
  replicas: 3

Prerequisites

• Kubernetes cluster 1.9 + (minikube also works)
• golang 1.11 +
• set GO111MODULE="on" env if source code is in $GOPATH

Presentation

Presentation deck

Tutorial

Check out the code according to following instruction and check the README file to follow the further instructions.

step 1

git checkout step-1

covers basic code and scaffolding setup

step 2

git checkout step-2

Covers how to define CRD types, register CRD's and generate client API's using go-client and generators It covers simple program that issues watch request to PodSet resource and print's resource state changes on console.

step 3

git checkout step-3

Covers functional controller using basic generated code. It shows how to issue watch requests and bring PodSet resource to desired state (reconciliation).

step 4

git checkout step-4

Covers fully functional controller using shared informers, listers and workqueues. It shows how to generate all those objects. At this point one could able to relate why controllers are written in particular way.

Note: This code is intended for educational purpose. While less focus is given on code quality aspect.

Credits

• https://github.com/kubernetes/sample-controller
• programming kubernetes by Stefan Schimanski, Michael Hausenblas