SpringBoot 2.3 introduced a feature to create OCI/Docker images by running ./gradlew bootBuildImage instead of having a Dockerfile and execute docker build .
When building on a Gitlab build server that is running inside a Kubernetes cluster there is no Docker daemon available though (no docker-in-docker service for security reasons). Instead images have to be build and uploaded using Google's "Kaniko" tool.
Is it possible to combine both somehow i.e. use "bootBuildImage" without a running Docker daemon?
It is possible by using Podman. Podman includes a daemon that implements a Docker-compatible API. On a local machine this can be started via podman system service --time 0 tcp://0.0.0.0:2375.
When running in Kubernetes (or generally in a container) you can use the container image from Quay: quay.io/containers/podman. Start the service in the background and the run your build. Something like this should work:
build:
image: my-java-builder
services:
- name: quay.io/containers/podman:v4.2.1
alias: docker
command: ["podman", "system", "service", "--time=0", "tcp://0.0.0.0:2375"]
variables:
DOCKER_HOST: tcp://docker:2375
script:
- ./gradlew bootBuildImage