K8s Learn

Demo presents how to deploy a Spring Boot application in the local Kubernetes cluster.

Requirements

• Java 17 (e.g. SAP Machine)
• Docker
• Kubectl
• k3d

Prepare Cluster

1. Launch Docker deamon
2. Create a local registry

   k3d registry create registry.localhost --port 5000

3. Build the Counter service and push it to the local registry

   .\counter-service-java\gradlew dockerBuildImage -p counter-service-java

   docker tag com.github.agabrys/counter-service:latest localhost:5000/com.github.agabrys/counter-service:latest

   docker push localhost:5000/com.github.agabrys/counter-service:latest

4. Build the Kubernetes controller and push it to the local registry

   .\kubernetes-controller-java\gradlew dockerBuildImage -p kubernetes-controller-java

   docker tag com.github.agabrys/kubernetes-controller:latest localhost:5000/com.github.agabrys/kubernetes-controller:latest

   docker push localhost:5000/com.github.agabrys/kubernetes-controller:latest

5. Create a local Kubernetes cluster with access to the local registry

   k3d cluster create -p "9080:80@loadbalancer" k8s-learn --registry-use k3d-registry.localhost:5000

6. Configure Kubernetes configuration

   kubectl apply -f ./counter-service.yaml

   kubectl apply -f ./kubernetes-controller.yaml

   The Counter service is configured to returns a number of deployments with the app=nginx label

The cluster needs a few seconds (30-60) to provision all pods, so please wait a moment before you start going through the demo steps.

Demo

Use the following steps to verify that the integration between the Kubernetes controller and the Counter service works properly.

1. Open the Counter service endpoints: http://localhost:9080/counter/value. It should return 0
2. Add the nginx1 deployment (with app=nginx)

   kubectl apply -f ./test-1.yaml

   The Counter service should return 1
3. Add the none-nginx deployment (without app=nginx)

   kubectl apply -f ./test-2.yaml

   The Counter service should return 1
4. Add the nginx2 and nginx3 deployments (with app=nginx)

   kubectl apply -f ./test-3.yaml

   The Counter service should return 3
5. Remove the nginx2 deployement

   kubectl delete deployment nginx2

   The Counter service should return 2
6. Remove the none-nginx deployment

   kubectl delete deployment none-nginx

   The Counter service should return 2

Notes

The project has been created in two days and almost all used technologies were new to me. I see a lot of fields to improve, but I didn't have enough time to work on it. Some examples:

• create a K8s namespace and use it instead of default
• use fieldSelector to gather less data when deployments are requested
• add tests to the K8s controller written by using kubernetes-client/java
• use more precise resource limits

The git commits are not descriptive. The main goal was to learn K8s, so I didn't focus on them too much (especially that nobody will read them 😉). Some examples of git messages which I usually write:

• https://github.com/jenkinsci/branch-api-plugin/pull/244/commits/0ba29aae1fbe421f9fc0b46bf50d14889da1233f
• https://github.com/jenkinsci/active-choices-plugin/pull/32/commits/04cf5ec8d39d63c907879cb91bcd498fe5d837a7