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



To build the jar use:

<sxh>
$ ./gradlew bootJar  --args='--server.port=8888'
Starting a Gradle Daemon, 1 busy and 1 stopped Daemons could not be reused, use --status for details

BUILD SUCCESSFUL in 11s
4 actionable tasks: 1 executed, 3 up-to-date

</sxh>

To run

<sxh>

$ java -jar build/libs/demo-0.0.1-SNAPSHOT.jar

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::                (v3.2.3)

2024-03-04T22:46:38.269+01:00  INFO 47724 --- [           main] com.example.demo.DemoApplication         : Starting DemoApplication v0.0.1-SNAPSHOT using Java 17.0.4 with PID 47724 (/mnt/d/1PROJEKTE/Kubernete-tutorials-springboot/build/libs/demo-0.0.1-SNAPSHOT.jar started by skip in /mnt/d/1PROJEKTE/Kubernete-tutorials-springboot)
2024-03-04T22:46:38.282+01:00  INFO 47724 --- [           main] com.example.demo.DemoApplication         : No active profile set, falling back to 1 default profile: "default"
^X^C2024-03-04T22:46:40.721+01:00  INFO 47724 --- [           main] o.s.b.a.e.web.EndpointLinksResolver
 : Exposing 1 endpoint(s) beneath base path '/actuator'
2024-03-04T22:46:41.296+01:00  INFO 47724 --- [           main] o.s.b.web.embedded.netty.NettyWebServer  : Netty started on port 8080
2024-03-04T22:46:41.311+01:00  INFO 47724 --- [           main] com.example.demo.DemoApplication         : Started DemoApplication in 4.003 seconds (process running for 4.858)
</sxh>


Building the image:

<sxh>
$ ./gradlew bootBuildImage

    [creator]     Adding label 'io.buildpacks.project.metadata'
    [creator]     Adding label 'org.opencontainers.image.title'
    [creator]     Adding label 'org.opencontainers.image.version'
    [creator]     Adding label 'org.springframework.boot.version'
    [creator]     Setting default process type 'web'
    [creator]     Saving docker.io/library/demo:0.0.1-SNAPSHOT...
    [creator]     *** Images (b57e814aa8fb):
    [creator]           docker.io/library/demo:0.0.1-SNAPSHOT
    [creator]     Adding cache layer 'paketo-buildpacks/syft:syft'
    [creator]     Adding cache layer 'buildpacksio/lifecycle:cache.sbom'

Successfully built image 'docker.io/library/demo:0.0.1-SNAPSHOT'


BUILD SUCCESSFUL in 1m 6s
5 actionable tasks: 1 executed, 4 up-to-date
skip@desktop:/mnt/d/1PROJEKTE/Kubernete-tutorials-springboot$ docker images
REPOSITORY                            TAG              IMAGE ID       CREATED        SIZE
paketobuildpacks/run-jammy-base       latest           ddb21b4d22de   6 days ago     111MB
gcr.io/k8s-minikube/kicbase           v0.0.42          dbc648475405   3 months ago   1.2GB
gcr.io/k8s-minikube/kicbase           v0.0.30          1312ccd2422d   2 years ago    1.14GB
demo                                  0.0.1-SNAPSHOT   b57e814aa8fb   44 years ago   307MB
paketobuildpacks/builder-jammy-base   latest           d00577c76e33   44 years ago   1.46GB
</sxh>


Running

<sxh>
docker run -p 8080:8080 demo:0.0.1-SNAPSHOT
Setting Active Processor Count to 20
Calculating JVM memory based on 30175084K available memory
For more information on this calculation, see https://paketo.io/docs/reference/java-reference/#memory-calculator
Calculated JVM Memory Configuration: -XX:MaxDirectMemorySize=10M -Xmx29783343K -XX:MaxMetaspaceSize=84540K -XX:ReservedCodeCacheSize=240M -Xss1M (Total Memory: 30175084K, Thread Count: 50, Loaded Class Count: 12512, Headroom: 0%)
Enabling Java Native Memory Tracking
Adding 137 container CA certificates to JVM truststore
Spring Cloud Bindings Enabled
Picked up JAVA_TOOL_OPTIONS: -Djava.security.properties=/layers/paketo-buildpacks_bellsoft-liberica/java-security-properties/java-security.properties -XX:+ExitOnOutOfMemoryError -XX:ActiveProcessorCount=20 -XX:MaxDirectMemorySize=10M -Xmx29783343K -XX:MaxMetaspaceSize=84540K -XX:ReservedCodeCacheSize=240M -Xss1M -XX:+UnlockDiagnosticVMOptions -XX:NativeMemoryTracking=summary -XX:+PrintNMTStatistics -Dorg.springframework.cloud.bindings.boot.enable=true

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::                (v3.2.3)
</sxh>



Generate deployment config

<sxh shell>
kubectl create deployment demo --image=springguides/demo --dry-run -o=yaml > deployment.yaml
echo --- >> deployment.yaml
kubectl create service clusterip demo --tcp=8080:8080 --dry-run -o=yaml >> deployment.yaml
</sxh>

Manifests are YAML files containing multiple resources separated by the "---"  separator. 


  * **Service in Kubernetes**: A service acts as an abstraction layer for a set of Pods, providing a network identity for them. This allows other applications within the cluster to discover and connect to these Pods using the service's name and port instead of individual Pod IPs.
  * **ClusterIP Service Type**: When you use clusterip, you're creating a service that has a virtual IP address assigned within the cluster. **This IP address is only accessible from within the cluster** and cannot be directly accessed from the outside world.
  * **Benefits**: ClusterIP services are useful for applications that only need to communicate with other services or Pods within the cluster. 





<sxh shell>

skip@desktop:/mnt/d/1PROJEKTE/Kubernete-tutorials-springboot$  kubectl get all
NAME                        READY   STATUS             RESTARTS   AGE
pod/demo-86795d784d-2bc82   0/1     ImagePullBackOff   0          91m

NAME                 TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)    AGE
service/demo         ClusterIP   10.101.245.55   <none>        8080/TCP   91m
service/kubernetes   ClusterIP   10.96.0.1       <none>        443/TCP    25h

NAME                   READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/demo   0/1     1            0           91m

NAME                              DESIRED   CURRENT   READY   AGE
replicaset.apps/demo-86795d784d   1         1         0       91m

</sxh>


Now you need to be able to connect to the application, which you have exposed as a Service in Kubernetes. One way to do that, which works great at development time, is to create an SSH tunnel:



<sxh shell>
kubectl port-forward svc/demo 8080:8080
</sxh>



**Kubernetes usually uses REMOTE images from repo.**
To fix:


**Step1:** 

Artificially add the image to the minikube cache.


Achtung: work around bug https://github.com/kubernetes/minikube/issues/18021

<sxh>
skip@desktop:/mnt/d/1PROJEKTE/Kubernete-tutorials-springboot$ docker image save -o image.tar springguides/demo:latest
skip@desktop:/mnt/d/1PROJEKTE/Kubernete-tutorials-springboot$ minikube image load image.tar
</sxh>


**Step2:** 

Use ''eval $(minikube docker-env)'' to switch to container cache within minikube.

After taht ''docker images'' will show you minikube containers.

<sxh shell>
skip@desktop:/mnt/d/1PROJEKTE/Kubernete-tutorials-springboot$ eval $(minikube docker-env)
skip@desktop:/mnt/d/1PROJEKTE/Kubernete-tutorials-springboot$ docker images
REPOSITORY                                TAG       IMAGE ID       CREATED        SIZE
docker                                    latest    e5fbe8997fd9   11 days ago    348MB
k8s.gcr.io/kube-apiserver                 v1.23.3   f40be0088a83   2 years ago    135MB
k8s.gcr.io/kube-controller-manager        v1.23.3   b07520cd7ab7   2 years ago    125MB
k8s.gcr.io/kube-scheduler                 v1.23.3   99a3486be4f2   2 years ago    53.5MB
k8s.gcr.io/kube-proxy                     v1.23.3   9b7cc9982109   2 years ago    112MB
k8s.gcr.io/etcd                           3.5.1-0   25f8c7f3da61   2 years ago    293MB
k8s.gcr.io/coredns/coredns                v1.8.6    a4ca41631cc7   2 years ago    46.8MB
k8s.gcr.io/pause                          3.6       6270bb605e12   2 years ago    683kB
kubernetesui/dashboard                    v2.3.1    e1482a24335a   2 years ago    220MB
kubernetesui/metrics-scraper              v1.0.7    7801cfc6d5c0   2 years ago    34.4MB
gcr.io/k8s-minikube/storage-provisioner   v5        6e38f40d628d   2 years ago    31.5MB
springguides/demo                         latest    b57e814aa8fb   44 years ago   307MB
</sxh>





Now finally you can run a container with image 'image: springguides/demo'

<sxh>
skip@desktop:/mnt/d/1PROJEKTE/Kubernete-tutorials-springboot$ kubectl apply -f deployment.yaml
deployment.apps/demo created
service/demo created
skip@desktop:/mnt/d/1PROJEKTE/Kubernete-tutorials-springboot$ kubectl get all
NAME                        READY   STATUS    RESTARTS   AGE
pod/demo-6f64658b59-swj5z   1/1     Running   0          3s

NAME                 TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
service/demo         ClusterIP   10.97.44.9   <none>        8080/TCP   3s
service/kubernetes   ClusterIP   10.96.0.1    <none>        443/TCP    26h

NAME                   READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/demo   1/1     1            1           3s

NAME                              DESIRED   CURRENT   READY   AGE
replicaset.apps/demo-6f64658b59   1         1         1       3s

</sxh>


Forwarding port 

<sxh>
kubectl port-forward svc/demo 8080:8080
</sxh>



kubectl: This is the command-line tool used to interact with a Kubernetes cluster.

port-forward: This is a subcommand of kubectl specifically designed for forwarding ports from Pods or Services within the cluster to your local machine.

svc/demo: This specifies the target resource for port forwarding. It indicates a Service named demo in the current namespace.

8080:8080: This defines the port mapping. The first 8080 represents the local port on your machine that will be used to access the forwarded service. The second 8080 indicates the port on the target service within the cluster.



You can now reach the service on 8080
<sxh>
curl localhost:8080/actuator/health
</sxh>