onobc / k8s-demo

Sample app that uses K8S config map property source

This is a sample app that shows how to use a Kubernetes config map as a property source in a Spring Boot app. Upon startup, the app prints out the value of the foo configuration property.

⚠️	The critical portion for this to work is settings spring.config.import=kubernetes: which must be escaped when specified in application.yml as spring.config.import: "kubernetes:"

Start Minikube

minikube start --cpus=4 --memory=8192

Build Image

./gradlew clean build bootBuildImage
docker tag demo:0.0.1-SNAPSHOT onobc/demo:1

Push Image to Minkube

minikube image load --pull=false "onobc/demo:1"
minikube image list

Create K8S Resources

kubectl apply -f configmap.yaml
kubectl apply -f clusterrole.yaml
kubectl apply -f deployment.yaml

Sanity Test App

Make the http 8080 port available over localhost w/ the following command:

kubectl port-forward svc/demo 8080:8080

In another terminal, invoke the actuator health endpoint by executing:

curl localhost:8080/actuator/health

which results in:

{"status":"UP","groups":["liveness","readiness"]}

View App Log

View the app logs w/ k9s or via kubectl such as:

kc get pods
kc logs pods/<enter-pod-name-from-previous-command>

You should see something like the following (notice the value of the foo var):

2023-12-24T04:06:40.338Z  INFO 1 --- [demo] [           main] o.s.b.a.e.web.EndpointLinksResolver      : Exposing 1 endpoint(s) beneath base path '/actuator'
2023-12-24T04:06:40.727Z  INFO 1 --- [demo] [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port 8080 (http) with context path ''
2023-12-24T04:06:40.853Z  INFO 1 --- [demo] [           main] com.example.demo.DemoApplication         : Started DemoApplication in 27.859 seconds (process running for 30.721)
****** FOO = bar
2023-12-24T04:06:46.353Z  INFO 1 --- [demo] [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2023-12-24T04:06:46.357Z  INFO 1 --- [demo] [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2023-12-24T04:06:46.364Z  INFO 1 --- [demo] [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 6 ms

Delete K8S Resources

kubectl delete -f deployment.yaml
kubectl delete -f clusterrole.yaml
kubectl delete -f configmap.yaml

Remote Debug

Make the jdwp 5005 port available over localhost w/ the following command:

kubectl port-forward svc/demo 5005:5005

Then attach a remote debugger to port localhost:5005

💡	If you want to debug the startup of the app you will need to edit deployment.yaml and set suspend=y in the JAVA_OPTS env var and then re-apply the resources.

References

• https://docs.spring.io/spring-cloud-kubernetes/reference/property-source-config.html

• https://spring.io/guides/gs/spring-boot-kubernetes/