Tutorial: Quarkus App with Docker

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1. Create a Simple Quarkus Application

1.1. Create the Project

Configure on quarkus.io and download as zip or push to github
Alternatively create the project per maven

You have to install maven before

Check the newest quarkus version https://quarkus.io/

mvn io.quarkus.platform:quarkus-maven-plugin:3.0.1.Final:create \
    -DprojectGroupId=at.htlleonding.vehicle \
    -DprojectArtifactId=vehicle-demo \
    -Dextensions="resteasy-reactive, resteasy-reactive-jackson, smallrye-openapi"

1.2. First Run of the Project

open a terminal

./mvnw clean quarkus:dev

1.3. Manual Check of the Running Project

1.3.1. Curl

open another terminal

curl http://localhost:8080/hello

output

Hello from RESTEasy Reactive

1.3.2. Intellij Rest Client

You can also use the intellij rest client:

1	Create folder `http-requests` and create (text-)file `requests.http`.
2	Write request GET http://localhost:8080/hello ###
3	Run request
4	In the Service-window the output is shown

1.4. Build a jar-File

build a jar-file (package)

./mvnw clean package
ls -lh ./target

result

-rw-r--r--   1 stuetz  staff   5.4K Mar 14 12:08 quarkus-docker-gh-actions-demo-0.1.0-SNAPSHOT.jar

we want to rename the jar-file to get rid of demo.
→ we will rename the jar-file

1.5. Rename the jar-File

rename the project into vehicle w/ version#

//...
<build>
  <finalName>vehicle-${version}</finalName>
  <plugins>
    //...
  </plugins>
</build>

There is also a property quarkus.package.output-name

build a jar-file (package)

./mvnw clean package -DskipTests

It produces the quarkus-run.jar file in the target/quarkus-app/ directory. Be aware that it’s not an uber-jar as the dependencies are copied into the target/quarkus-app/lib/ directory.

ls -l target

result

-rw-r--r--  1 stuetz  staff   173K Apr 29 13:30 vehicle-1.0.0-SNAPSHOT.jar

run the app

java -jar target/vehicle-1.0.0-SNAPSHOT.jar

result

no main manifest attribute, in target/vehicle-1.0.0-SNAPSHOT.jar

but there is also

tree target/quarkus-app

target/quarkus-app
├── app
│     └── vehicle-1.0.0-SNAPSHOT.jar
├── lib
│     ├── boot
│     │     ├── ...
│     │     ├── io.quarkus.quarkus-bootstrap-runner-3.0.1.Final.jar
│     │     └── ...
│     └── main
│         ├── ...
│         ├── com.fasterxml.jackson.core.jackson-annotations-2.14.2.jar
│         └── ...
├── quarkus
│   ├── generated-bytecode.jar
│   ├── quarkus-application.dat
│   └── transformed-bytecode.jar
├── quarkus-app-dependencies.txt
└── quarkus-run.jar

run the app

java -jar target/quarkus-app/quarkus-run.jar

the libraries are in the lib-folder available

2. Run a local Docker Container

To dockerize the quarkus application into a docker image, there are several options available:
- Usage of a Dockerfile
- Using a library (i.e. jib) to build an image
- …

2.1. Using a Dockerfile

When creating a quarkus project, you get pre-configured Dockerfiles
Please notice:
- It is possible to package the quarkus app with all dependent libraries. This is called an uber-jar.
- But it is more performant to create a layer for the libraries and a layer for the quarkus app. So it is very fast, when you only have changes in the quarkus app. Only a very small layer would be created after the code changes.
- so the pre-configured Dockerfiles in src/main/docker the layers

2.1.1. Create the jar-file

./mvnw clean package

result

-rw-r--r--  1 stuetz  staff   173K Apr 29 13:42 vehicle-1.0.0-SNAPSHOT.jar

2.1.2. Create the Docker Image

docker build -f src/main/Docker/Dockerfile.jvm -t htl-leonding/vehicle .

docker image ls

result

REPOSITORY                                TAG              IMAGE ID       CREATED             SIZE
htl-leonding/vehicle                      latest           49b4b82d75fa   7 seconds ago       440MB

2.1.3. Start the Docker Container

docker run -i --rm -p 8080:8080 htl-leonding/vehicle

In the Dockerfile.jvm you find in the comments all commands

result

Starting the Java application using /opt/jboss/container/java/run/run-java.sh ...
INFO exec  java -Dquarkus.http.host=0.0.0.0 -Djava.util.logging.manager=org.jboss.logmanager.LogManager -XX:MaxRAMPercentage=50.0 -XX:+UseParallelGC -XX:MinHeapFreeRatio=10 -XX:MaxHeapFreeRatio=20 -XX:GCTimeRatio=4 -XX:AdaptiveSizePolicyWeight=90 -XX:+ExitOnOutOfMemoryError -cp "." -jar /deployments/quarkus-run.jar
__  ____  __  _____   ___  __ ____  ______
 --/ __ \/ / / / _ | / _ \/ //_/ / / / __/
 -/ /_/ / /_/ / __ |/ , _/ ,< / /_/ /\ \
--\___\_\____/_/ |_/_/|_/_/|_|\____/___/
2023-04-29 11:54:21,899 INFO  [io.quarkus] (main) vehicle-demo 1.0.0-SNAPSHOT on JVM (powered by Quarkus 3.0.1.Final) started in 0.425s. Listening on: http://0.0.0.0:8080
2023-04-29 11:54:21,917 INFO  [io.quarkus] (main) Profile prod activated.
2023-04-29 11:54:21,917 INFO  [io.quarkus] (main) Installed features: [cdi, resteasy-reactive, resteasy-reactive-jackson, smallrye-context-propagation, smallrye-openapi, vertx]

Use the REST-client for checking if the app works.

2.2. Using Jib

There is a Library called Jib (Java Image Builder) from Google which makes it possible to build a Docker image without installing Docker
Fortunately Quarkus has already implemented Jib

2.2.1. Add Jib-Dependency to pom.xml

./mvnw quarkus:add-extension -Dextensions='container-image-jib'

2.2.2. Configure application.properties

quarkus.container-image.build=true  (1)
quarkus.container-image.group=htl-leonding
quarkus.container-image.name=vehicle
quarkus.container-image.tag=latest
quarkus.jib.ports=8080

1	this property is mandatory for building the docker image

2.2.3. Compile App and Build Image

./mvnw clean package

result

[INFO] Scanning for projects...
[WARNING]
[WARNING] Some problems were encountered while building the effective model for at.htlleonding.vehicle:vehicle-demo:jar:1.0.0-SNAPSHOT
[WARNING] The expression ${version} is deprecated. Please use ${project.version} instead.
[WARNING] The expression ${version} is deprecated. Please use ${project.version} instead.
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING]
[INFO]
[INFO] ----------------< at.htlleonding.vehicle:vehicle-demo >-----------------
[INFO] Building vehicle-demo 1.0.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ vehicle-demo ---
[INFO] Deleting /Users/stuetz/SynologyDrive/htl/skripten/themen/github/quarkus-docker-gh-actions-demo/labs/vehicle-demo/target
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ vehicle-demo ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 2 resources
[INFO]
[INFO] --- quarkus-maven-plugin:3.0.1.Final:generate-code (default) @ vehicle-demo ---
[INFO]
[INFO] --- maven-compiler-plugin:3.11.0:compile (default-compile) @ vehicle-demo ---
[INFO] Changes detected - recompiling the module! :source
[INFO] Compiling 1 source file with javac [debug release 17] to target/classes
[INFO]
[INFO] --- quarkus-maven-plugin:3.0.1.Final:generate-code-tests (default) @ vehicle-demo ---
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ vehicle-demo ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory /Users/stuetz/SynologyDrive/htl/skripten/themen/github/quarkus-docker-gh-actions-demo/labs/vehicle-demo/src/test/resources
[INFO]
[INFO] --- maven-compiler-plugin:3.11.0:testCompile (default-testCompile) @ vehicle-demo ---
[INFO] Changes detected - recompiling the module! :dependency
[INFO] Compiling 2 source files with javac [debug release 17] to target/test-classes
[INFO]
[INFO] --- maven-surefire-plugin:3.0.0:test (default-test) @ vehicle-demo ---
[INFO] Using auto detected provider org.apache.maven.surefire.junitplatform.JUnitPlatformProvider
[INFO]
[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running at.htlleonding.vehicle.GreetingResourceTest
2023-04-29 14:16:32,049 INFO  [io.quarkus] (main) vehicle-demo 1.0.0-SNAPSHOT on JVM (powered by Quarkus 3.0.1.Final) started in 1.041s. Listening on: http://localhost:8081
2023-04-29 14:16:32,050 INFO  [io.quarkus] (main) Profile test activated.
2023-04-29 14:16:32,051 INFO  [io.quarkus] (main) Installed features: [cdi, resteasy-reactive, resteasy-reactive-jackson, smallrye-context-propagation, smallrye-openapi, swagger-ui, vertx]
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 2.703 s - in at.htlleonding.vehicle.GreetingResourceTest
2023-04-29 14:16:32,713 INFO  [io.quarkus] (main) vehicle-demo stopped in 0.098s
[INFO]
[INFO] Results:
[INFO]
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO]
[INFO]
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ vehicle-demo ---
[INFO] Building jar: /Users/stuetz/SynologyDrive/htl/skripten/themen/github/quarkus-docker-gh-actions-demo/labs/vehicle-demo/target/vehicle-1.0.0-SNAPSHOT.jar
[INFO]
[INFO] --- quarkus-maven-plugin:3.0.1.Final:build (default) @ vehicle-demo ---
[INFO] [io.quarkus.container.image.jib.deployment.JibProcessor] Starting (local) container image build for jar using jib.
[INFO] [io.quarkus.container.image.jib.deployment.JibProcessor] Using docker to run the native image builder
[WARNING] [io.quarkus.container.image.jib.deployment.JibProcessor] Base image 'registry.access.redhat.com/ubi8/openjdk-17-runtime:1.15' does not use a specific image digest - build may not be reproducible
[INFO] [io.quarkus.container.image.jib.deployment.JibProcessor] Using base image with digest: sha256:f921cf1f9147e4b306908f3bcb61dd215b4a51970f8db560ede02ee6a492fa99
[INFO] [io.quarkus.container.image.jib.deployment.JibProcessor] Container entrypoint set to [java, -Djava.util.logging.manager=org.jboss.logmanager.LogManager, -jar, quarkus-run.jar]
[INFO] [io.quarkus.container.image.jib.deployment.JibProcessor] Created container image htl-leonding/vehicle (sha256:ea1f3d84df3221e0ce05527735b558bf410132712113a50f6a59064c7bcdaf1e)

[INFO] [io.quarkus.deployment.QuarkusAugmentor] Quarkus augmentation completed in 5496ms
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  10.570 s
[INFO] Finished at: 2023-04-29T14:16:38+02:00
[INFO] ------------------------------------------------------------------------

docker image ls

REPOSITORY                                          TAG              IMAGE ID       CREATED         SIZE
htl-leonding/vehicle                                latest           de4acf85c454   4 minutes ago   382MB

2.2.4. Start the Docker Container

docker run --rm -p 8080:8080 htl-leonding/vehicle

Use the REST-client for checking if the app works.

3. Run local docker-compose

Now we have the docker image locally.

3.1. Create docker-compose.yaml

We need a docker-compose.yaml - file

services:
  backend:
    image: htl-leonding/vehicle:latest
    ports:
      - "8080:8080"
    networks:
      - vehicle

networks:
  vehicle:
    name: quarkus-vehicle-network

3.2. Start docker-compose

docker compose up -d

Use the REST-client for checking if the app works.

3.3. Stop docker-compose

docker compose down

4. Run a local docker-compose with Database

4.1. Add Dependencies for the database

./mvnw quarkus:add-extension -Dextensions='jdbc-postgresql, hibernate-orm-panache'

4.2. Add code for accessing database

Vehicle.java

package at.htlleonding.vehicle;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

@Entity
public class Vehicle {

    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private
    Long id;

    private String brand;
    private String model;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    @Override
    public String toString() {
        return String.format("%s %s", brand, model);
    }
}

VehicleDto.java

package at.htlleonding.vehicle;

public record VehicleDto (Long id, String brand, String model) {}

VehicleRepository.java

package at.htlleonding.vehicle;

import io.quarkus.hibernate.orm.panache.PanacheRepository;
import jakarta.enterprise.context.ApplicationScoped;

@ApplicationScoped
public class VehicleRepository implements PanacheRepository<Vehicle> {
}

VehicleResource.java

package at.htlleonding.vehicle;

import jakarta.inject.Inject;
import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.Produces;
import jakarta.ws.rs.core.MediaType;

import java.util.List;

@Path("/vehicle")
public class VehicleResource {

    @Inject
    VehicleRepository vehicleRepository;

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public List<Vehicle> listAll() {
        return vehicleRepository.listAll();
    }
}

http-requests/requests.http

GET http://localhost:8080/hello

###

GET http://localhost:8080/vehicle

####

src/main/resources/insert.sql

insert into vehicle (brand, model) values ('Opel', 'Kadett');
insert into vehicle (brand, model) values ('VW', 'Käfer');

add assertj-core to dependencies in pom.xml

  <dependencies>
    ...
    <dependency>
      <groupId>org.assertj</groupId>
      <artifactId>assertj-core</artifactId>
      <version>3.24.2</version>
      <scope>test</scope>
    </dependency>
  </dependencies>

src/main/test/java/at/htlleonding/vehicle/VehicleResourceTest.java

package at.htlleonding.vehicle;

import io.quarkus.test.junit.QuarkusTest;
import org.junit.jupiter.api.Test;

import java.util.LinkedList;
import java.util.List;

import static io.restassured.RestAssured.given;

import static org.assertj.core.api.Assertions.assertThat;

@QuarkusTest
public class VehicleResourceTest {

    @Test
    public void testHelloEndpoint() {

        List<VehicleDto> expectedVehicles = List.of(
                new VehicleDto(2L, "VW", "Käfer"),
                new VehicleDto(1L, "Opel", "Kadett")
        );

        List<VehicleDto> retrievedVehicles = new LinkedList<>();
        retrievedVehicles = given()
                .when().get("/vehicle")
                .then()
                .statusCode(200)
                .extract().body().jsonPath().getList(".", VehicleDto.class);

        assertThat(retrievedVehicles).hasSize(2)
                .usingRecursiveComparison()
                .ignoringFields("id")
                .ignoringCollectionOrder()
                .isEqualTo(expectedVehicles);
    }

}

src/main/resources/application.properties

# datasource configuration
quarkus.datasource.db-kind = postgresql
quarkus.datasource.username = app
quarkus.datasource.password = app
quarkus.datasource.jdbc.url = jdbc:postgresql://localhost:5432/db

# drop and create the database at startup (use `update` to only update the schema)
quarkus.hibernate-orm.database.generation=drop-and-create
%prod.quarkus.hibernate-orm.sql-load-script=import.sql (1)

#quarkus.package.type=uber-jar

quarkus.container-image.build=true
quarkus.container-image.group=htl-leonding
quarkus.container-image.name=vehicle
quarkus.container-image.tag=latest
quarkus.jib.ports=8080

1	For importing data in prod-profile

4.3. Build the docker image

./mvnw clean package -DskipTests -Dquarkus.container-image.build=true

Because the ide is running on linux/arm64/v8 - architecture, we have to tell jib to create an linux/amd64 image → -Dquarkus.container-image.build=true

4.4. Create the docker-compose.yaml for development

For starting only the database and pgadmin.
- You could also use dev-services for starting a database.
The quarkus-app ist startet in dev-mode w/o docker.

docker-compose-postgres.yaml

services:

  db:
    container_name: postgres
    image: postgres:15.2-alpine
    restart: unless-stopped
    environment:
      POSTGRES_USER: app
      POSTGRES_PASSWORD: app
      POSTGRES_DB: db
    ports:
      - 5432:5432
    volumes:
      - ./db-postgres/db:/var/lib/postgresql/data
      - ./db-postgres/import:/import
    networks:
      - postgres

#  adminer:
#    image: adminer
#    restart: always
#    ports:
#      - 8090:8080

# https://github.com/khezen/compose-postgres/blob/master/docker-compose.yml
  pgadmin:
    container_name: pgadmin
    image: dpage/pgadmin4:7.0
    environment:
      PGADMIN_DEFAULT_EMAIL: ${PGADMIN_DEFAULT_EMAIL:-pgadmin4@pgadmin.org}
      PGADMIN_DEFAULT_PASSWORD: ${PGADMIN_DEFAULT_PASSWORD:-admin}
      PGADMIN_CONFIG_SERVER_MODE: 'False'
    volumes:
      - ./db-postgres/pgadmin:/root/.pgadmin
    ports:
      - 8090:80
    networks:
      - postgres
    restart: unless-stopped

networks:
  postgres:
    driver: bridge

start

docker compose -f docker-compose-postgres.yaml up -d

stop

docker compose -f docker-compose-postgres.yaml down

4.5. Create the docker-compose.yaml for production

docker-compose-all-services.yaml

services:

  db:
    container_name: postgres
    image: postgres:15.2-alpine
    restart: unless-stopped
    environment:
      POSTGRES_USER: app
      POSTGRES_PASSWORD: app
      POSTGRES_DB: db
    ports:
      - 5432:5432
    volumes:
      - ./db-postgres/db:/var/lib/postgresql/data
      - ./db-postgres/import:/import
    networks:
      - vehicle

# https://github.com/khezen/compose-postgres/blob/master/docker-compose.yml
  pgadmin:
    container_name: pgadmin
    image: dpage/pgadmin4:7.0
    environment:
      PGADMIN_DEFAULT_EMAIL: ${PGADMIN_DEFAULT_EMAIL:-pgadmin4@pgadmin.org}
      PGADMIN_DEFAULT_PASSWORD: ${PGADMIN_DEFAULT_PASSWORD:-admin}
      PGADMIN_CONFIG_SERVER_MODE: 'False'
    volumes:
      - ./db-postgres/pgadmin:/root/.pgadmin
    ports:
      - 8090:80
    networks:
      - vehicle
    restart: unless-stopped

  backend:
    image: htl-leonding/vehicle:latest
    restart: unless-stopped
    environment:
      QUARKUS_DATASOURCE_JDBC_URL: jdbc:postgresql://db:5432/db
      QUARKUS_DATASOURCE_USERNAME: app
      QUARKUS_DATASOURCE_PASSWORD: app
    ports:
      - "8080:8080"
    depends_on:
      - db
    networks:
      - vehicle


networks:
  vehicle:
    name: quarkus-vehicle-network
    driver: bridge

start

docker compose -f docker-compose-all-services.yaml up -d

stop

docker compose -f docker-compose-all-services.yaml down

5. CI - Deploy to github-packages

sources:

5.1. Create a basic pipeline

When you create a quarkus-project with a jib-dependency, you get a sample ci.yml.

## A basic GitHub Actions workflow for your Quarkus application.

name: CI build

on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]
  workflow_dispatch:

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout gh-repo
        uses: actions/checkout@v3

      - name: Set up JDK 17
        uses: actions/setup-java@v3
        with:
          java-version: 17
          distribution: temurin
          cache: maven

      - name: Build
        run: |
          ./mvnw package -B
          docker image ls

After pushing this file, the first error occurs

Figure 1. database-service is missing

we could skip tests, or
we use testcontainers
- so we configure quarkus to use testcontainers in test-profile

application.properties

# datasource configuration
%dev.quarkus.datasource.db-kind = postgresql  (1)
%dev.quarkus.datasource.username = app
%dev.quarkus.datasource.password = app
%dev.quarkus.datasource.jdbc.url = jdbc:postgresql://localhost:5432/db

%prod.quarkus.datasource.db-kind = postgresql  (2)
%prod.quarkus.datasource.username = app
%prod.quarkus.datasource.password = app
%prod.quarkus.datasource.jdbc.url = jdbc:postgresql://localhost:5432/db

# drop and create the database at startup (use `update` to only update the schema)
quarkus.hibernate-orm.database.generation=drop-and-create
%prod.quarkus.hibernate-orm.sql-load-script=import.sql

#quarkus.package.type=uber-jar

quarkus.container-image.build=true
quarkus.container-image.group=htl-leonding
quarkus.container-image.registry=ghcr.io
quarkus.container-image.name=vehicle
quarkus.container-image.tag=latest
quarkus.jib.ports=8080

%test.quarkus.datasource.devservices.enabled=true (3)

1	for dev-profile use local docker-compose-database-service
2	for prod-profile use local docker-compose-database-service
3	activate devservices for databases - because we provide only db-credentials for test- and prod-profile, in test-profile we use a postgres-testcontainer

You see, the docker image is built, we can continue to publish this docker image into gh-packages
Because using the testcontainer is consuming a lot of github-resources (you normally have to pay), so we will skip tests, while developing the pipeline.

6. Publishing to gh-packages

source: Publishing and installing a package with GitHub Actions

You can use a GITHUB_TOKEN in a GitHub Actions workflow to delete or restore a package using the REST API, if the token has admin permission to the package. Repositories that publish packages using a workflow, and repositories that you have explicitly connected to packages, are automatically granted admin permission to packages in the repository.

— github-docs

github provides a token to authenticate (Automatic token authentication)

.github/workflows/ci.yaml

name: CI build

on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]
  workflow_dispatch:

env:
  REGISTRY: ghcr.io
  IMAGE_NAME: ${{ github.repository }}
  PROJECT_NAME: vehicle
  PROJECT_VERSION: latest

jobs:
  build-and-push-image:
    runs-on: ubuntu-latest

    steps:
      - name: Checkout gh-repo
        uses: actions/checkout@v3

      - name: Set up JDK 17
        uses: actions/setup-java@v3
        with:
          java-version: 17
          distribution: temurin
          cache: maven

      - name: Log in to the Container registry
        uses: docker/login-action@65b78e6e13532edd9afa3aa52ac7964289d1a9c1
        with:
          registry: ${{ env.REGISTRY }}
          username: ${{ github.actor }}
          password: ${{ secrets.MY_GITHUB_TOKEN }}

      - name: Build
        run: ./mvnw package -DskipTests -B

      - name: Push to packages
        run: docker push ${{ env.REGISTRY }}/${{ github.actor }}/${{ env.PROJECT_NAME }}:${{ env.PROJECT_VERSION }}

in the first attempt when using the provided ${{ secrets.GITHUB_TOKEN }} did not work:
- So in the repository a token with package-read-permission was created
- A repository-scoped secret was created with this token → ${{ secrets.MY_GITHUB_TOKEN }}
- Now it worked
  - Maybe this happened, because the repository was located in a github-organization
Instead of the Docker-login-action you could login with
- docker login -u ${{ github.actor }} -p ${{ secrets.MY_GITHUB_TOKEN }} ${{ env.REGISTRY }}
In the Build-Step you can omit -DskipTests
Instead of docker push … it would be possible to use mvn install - but in this case you have to supply the registry to the pom-file.

6.1. Configure permissions of GITHUB_TOKEN

As in GitHub Docs explained, it is possible to modify the default permissions granted to the GITHUB_TOKEN

This is maybe the better way than creating a new token (MY_GITHUB_TOKEN)

6.2. Make package public

To access the registry → https://github.com/<your_user_name>?tab=packages