Emoji

Emoji is a sample application to demonstrate how to build a Kubernetes Operator. The operator monitor the Emoji Custom Resources and publish them in an API. To know more about this application, check Programmez #237 on programmez.com

Design

The application design looks like below:

• An Emoji CRD allow to declare Emojis in Kubernetes
• A controller get all the Emojis from Kubernetes and synchronize them with the application. Once done, it publishes the status back to the resource.

Building and installing the application

To build the application, you must have make, go, kustomize and docker installed on your instance. Set the REGISTRY variable and run make build-docker like in the example below:

cd app
export REGISTRY=registry:5000
make build-docker

To install the application, set the REGISTRY variable, run change the image settings in the kustomization.yaml file and run a kubectl apply command:

export REGISTRY=registry:5000
kustomize edit set image emojis-app=${REGISTRY}/emojis-app:latest
kubectl apply -k .

To test the application, connect to port 8080 and run a curl command like below; It should return an empty JSON and an HTTP-200 status code:

kubectl port-forward svc/emojis 8080:8080
curl -v 127.0.0.1:8080

Controller example

This project contains a step by step example of how to build a controller. Each branch contains a step. To work with it, go to master which has no operator at all, only the application. The main steps are:

• operator/01-initialization contains the code scaffold
• operator/02-namespace-operator changes the operator so that it monitors a single namespace
• operator/03-crd-and-controller creates en empty emoji CRD and controller
• operator/04-specify-emoji-type add expected types to the CRD
• operator/05-implement-support implements a status.supported properties that tells if the Emoji is supported
• operator/06-implement-finalizer implements a finalizer to manage resource deletion
• operator/07-implement-applogic adds the logic to interact with the api
• operator/08-deployment perform the last changes to deploy the controller