A simple Gradle plugin to build very simple Spring Boot application Docker images.

Just Docker, Java, and your Spring Boot application

More specifically, this plugin automates the best practices described in the Spring Boot Container Images documentation by

• Hooking into the bootJar task of the Spring Boot Gradle Plugin
• Extracting the application layers
• Generating a Dockerfile
• Performing the docker build
• Pushing to a registry

Some additional features include

• Optional support for non-layered images that just java -jar application.jar
• Easy to integrate with Skaffold a custom build stage

Requirements

The Docker client needs to be installed locally with access to a Docker daemon. If pushing the image, docker login needs to be performed for the desired image registry.

Primary tasks

• buildSimpleBootImage
  • NOTE if using buildx, the default, pushing to a registry can be optimized into this same task by setting the extension property simpleBootImage.push to true.
• pushSimpleBootImage

Configuration

This plugin adds an extension named springBootImage; however, the defaults use a combination of gradle properties and environment variables to adapt easily to CI/CD and Skaffold builds.

The properties of the extension are:

Name	Description	Default
baseImage		Property imageBase or "eclipse-temurin:17"
cacheFrom		Property imageCacheFrom
cacheTo		Property imageCacheTo
exportPort		8080
fullyQualifiedImageName		Environment variable IMAGE or uses imageRepo, imageName, and tags
imageName	Name part of {repo}/{name}:{tag}	Property imageName or project.name
imageRepo	Repo part of {repo}/{name}:{tag}	Property imageRepo
layered		Property imageLayered or true
platforms	os/arch list supported by buildx	Default for builder
pullForBuild		Property imagePull or false
push		Property imagePush or Environment variable PUSH_IMAGE or false
tags	Tag part of {repo}/{name}:{tag}	["latest", project.version]
useBuildx		true
labels.description		project.description
labels.extra	Map of extra labels to apply	[:]
labels.revision		Property git.commit
labels.sourceUrl		If environment variable GITHUB_REPOSITORY, then https://github.com/${GITHUB_REPOSITORY}
labels.title		project.name
labels.version		Property imageVersion or project.version

Examples

Skaffold configuration

skaffold.yaml:

# nonk8s
apiVersion: skaffold/v3
kind: Config
metadata:
  name: app-dev
build:
  artifacts:
    - image: app-dev
      custom:
        buildCommand: ./gradlew pushSimpleBootImage
        dependencies:
          paths:
            - build.gradle
            - src/main/java
            - src/main/resources
profiles:
  - name: windows
    build:
      artifacts:
        - image: app-dev
          custom:
            # override this since Windows needs backslash'y paths
            buildCommand: .\gradlew pushSimpleBootImage
manifests:
  rawYaml:
    - k8s/*.yml

In build.gradle, you should also add the following to hook into the test flag.

test.onlyIf { !System.getenv('SKIP_TESTS') }

GitHub Actions Workflow

Single platform:

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v2

      - name: Login to image registry
        uses: docker/login-action@v2
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Gradle build and push
        uses: gradle/gradle-build-action@v2
        with:
          arguments: |
            -PimageRepo=ghcr.io/${{ github.actor }}
            -PimagePush=true 
            -PimageCacheFrom=type=gha
            -PimageCacheTo=type=gha,mode=max
            buildSimpleBootImage

and multi-platform using buildx:

    steps:
      - name: Setup Docker Buildx
        uses: docker/setup-buildx-action@v2

      - name: Set up QEMU
        uses: docker/setup-qemu-action@v2.0.0

      - name: Login to image registry
        uses: docker/login-action@v2
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Gradle build and push
        uses: gradle/gradle-build-action@v2
        with:
          arguments: |
            -PimageRepo=ghcr.io/${{ github.actor }}
            -PimagePlatforms=linux/amd64,linux/arm64
            -PimagePush=true 
            -PimageCacheFrom=type=gha
            -PimageCacheTo=type=gha,mode=max
            buildSimpleBootImage