Docker Java Spring Boot Test Application
Install WSL - Offical Instructions
Install Docker Desktop on Windows Official Instructions
Install Docker engine on Linux Official Instructions
Open Linux Terminal
sudo apt install unzip zip
curl -s "https://get.sdkman.io" | bash
source "$HOME/.sdkman/bin/sdkman-init.sh"
check that the installation is successful
sdk version
Install latest stable java
sdk install java
Install Spring Boot
sdk install springboot
Create a simple Spring web application
spring init --dependencies=web demo-application
Test that the application works
cd demo-application
./mvnw spring-boot:run
You should be able to navigate to the app via a browser and see the default placeholder page
Update the default code with an endpoint.
Open the file demo-application\src\main\java\com\example\demoapplication\DemoApplication.java and replace the contents
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@SpringBootApplication
@RestController
public class DemoApplication {
@RequestMapping("/")
public String home() {
return "Hello Everybody!";
}
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}
Restart the app and you should see content on the default homepage.
Copy the files Dockerfile and docker-compose.yml into the root level of the demo application. Then run the following command
docker compose build --no-cache demo-application
You can start the application using the command
docker compose up -d
Shut down the container with
docker compose down
You can now work with the Application in an IDE
Create a launch.json file in the .vscode folder if one doesn't exist already.
Add the following snippet
{
"type": "java",
"name": "Attach to Remote Program",
"request": "attach",
"hostName": "localhost",
"port": 8000
}
You can now select the option called "Attach to Remote Program" in the debug dropdown and attach to the instance running within the container. You will also be able to click the “Hot Module Swap” button (the lightning bolt icon) and VS Code will update the running application. Refresh the link to view the results
Double click on the file docker-compose.yml and click on the double pointer next to the word services. This will run docker compose up.
Now create a Remote Debug configuration and set the port to 8000. It should show that the remote session is connected.
You can now apply breakpoints and dynamically modify code using the Build -> Recomppile... menu item or pressing CTRL-SHIFT-F9
Install Kubernetes or activate in the Docker Desktop settings within Windows
Activate Kubernetes Desktop. From the command line run the following command. Get the latest version by checking the Web UI Dashboard Page. As of the time of writing the command is
kubectl apply -f https://raw.githubusercontent.com/kubernetes/dashboard/v2.5.0/aio/deploy/recommended.yaml
You should now see multiple apps in the "Container / Apps" section of the Docker desktop application.
Now patch the deployment to disable the login screen (Don't do this is prod)
kubectl edit deployment kubernetes-dashboard -n kubernetes-dashboard
Text editor will open. Look for the section /spec/template/spec/containers/0/args/. Approx line 41 in v2.5.0. Add the following line
- --enable-skip-login
The entire section should now look like the following
spec:
containers:
- args:
- --auto-generate-certificates
- --namespace=kubernetes-dashboard
- --enable-skip-login
Exit the text editor and the updated setting should be applied.
Now run the command to login to the dashboard
kubectl proxy
You should see the following message
Starting to serve on 127.0.0.1:8001
You can now login to the dashboard
Stop that running and install the Metrics Server.
Run the following command
kubectl apply -f https://github.com/kubernetes-sigs/metrics-server/releases/latest/download/components.yaml
You will again need to edit the deployment to allow for insecure connections (again don't do this on prod)
kubectl edit deployment metrics-server -n kube-system
Add the following at approx line 45
- --kubelet-insecure-tls
The Section should now look like
spec:
containers:
- args:
- --cert-dir=/tmp
- --secure-port=4443
- --kubelet-preferred-address-types=InternalIP,ExternalIP,Hostname
- --kubelet-use-node-status-port
- --metric-resolution=15s
- --kubelet-insecure-tls
In order to use Docker with Kubernetes we will need to build a simple docker image (ie not using Docker Compose as above)
Navigate to the demo-application directory and run the following command
docker build -t pram/demo-application .
Running docker images should show the following
C:\Users\pram\working\github\docker-java-spring-boot\demo-application>docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
pram/demo-application latest c48df267cd8a 49 seconds ago 426MB
Run the following to upload to Docker Hub. First login to the hub
C:\Users\pram\working\github\docker-java-spring-boot\demo-application>docker login
Login with your Docker ID to push and pull images from Docker Hub. If you don't have a Docker ID, head over to https://hub.docker.com to create one.
Username: pram
Password:
Login Succeeded
To Upload
docker push pram/demo-application
Once uploaded the image should be visible on the Docker hub.
Check that you can run the container in standalone mode
docker container run -d -p 8080:8080 -it --name demo-application pram/demo-application:latest
You should be able to navigate to the landing page
Create a Deployment Manifest file for the Kubernetes deployment called k8-demo-application-deployment.yml
Use the Following Site to generate the deployment file.
Create a deployment by running the command
kubectl create -f k8-demo-application-deployment.yml
You should see the following output
C:\Users\pram\working\github\docker-java-spring-boot>kubectl create -f k8-demo-application-deployment.yml
ddeployment.apps/demo-application created
Confirm that the deployment has been created by running kubectl get deployments
C:\Users\pram\working\github\docker-java-spring-boot>kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
demo-application 1/1 1 1 46s
You can get further information by running kubectl get deployments/demo-application and kubectl describe deployments/demo-application
Create the service manifest file. You can use the following site to generate the template. Make sure that the selector in the service matches that in the deployment manifest.
Run the following to create the service
kubectl apply -f k8-demo-application-service.yml
C:\Users\pram\working\github\docker-java-spring-boot>kubectl apply -f k8-demo-application-service.yml
service/demo-application created
Once the service starts you should be able to access the app
To stop the running application you can issue the following command
kubectl scale --replicas=0 deployment/demo-application