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type Reference
title Dockerfile and Image Structure
description Layer-by-layer breakdown of the Dockerfile, SDKMAN configuration, ARG-controlled versions, entrypoint behavior, and build dependencies required for native-image compilation.
tags
dockerfile
sdkman
graalvm
build
entrypoint

Dockerfile and Image Structure

The entire image is defined in a single Dockerfile at the repository root. It builds a Debian-based container with SDKMAN-managed Java and Maven toolchains.

Base image and layers

FROM debian:stable-slim

The image uses debian:stable-slim for minimal footprint. All setup is done in a single RUN instruction:

  1. System dependencies — installs OS packages, sets locale.
  2. SDKMAN install — fetches SDKMAN, writes its config.
  3. Java + Maven install — sources SDKMAN, runs sdk install for both tools, then cleans up archive/temp files.

Version control via ARGs

ARG JAVA_VERSION="25.1.3-graalce"
ARG MAVEN_VERSION="3.9.16"

These ARG directives are the single source of truth for installed tool versions. To upgrade GraalVM or Maven, change these values and update the README version table to match.

The image label and git tag convention reflect the GraalVM version (e.g. 25-graalce).

SDKMAN configuration

SDKMAN is configured in three lines written to $SDKMAN_DIR/etc/config:

Setting Value Purpose
sdkman_auto_answer true Non-interactive installs (no prompts)
sdkman_auto_selfupdate false Prevents SDKMAN version drift at build time
sdkman_insecure_ssl true Compatibility with some corporate proxy environments

The SDKMAN directory is /root/.sdkman (set via ENV SDKMAN_DIR).

System build packages

These packages are installed and must not be removed — they are required for GraalVM native-image compilation:

  • build-essential — C/C++ compiler toolchain
  • libz-dev, zlib1g-dev — compression libraries needed by native-image
  • ca-certificates — TLS trust store
  • fontconfig, locales — locale and font support for JVM

Entrypoint script

bin/entrypoint.sh is a three-line shell script:

#!/bin/bash
source /root/.bashrc && mvn "$@"

It sources .bashrc to activate the SDKMAN environment (which adds mvn and java to PATH), then forwards all container arguments to Maven. The Dockerfile sets SHELL ["/bin/bash", "-i", "-c"] and ENTRYPOINT ["/root/entrypoint.sh"].

Without sourcing .bashrc, mvn would not be found when the container starts — this is the most common cause of "command not found" errors when users override the entrypoint with a shell.

Helper scripts

Script Purpose
bin/build.sh Local no-cache Docker build, tags as :latest
bin/push.sh Pushes :latest to Docker Hub (manual testing only)

CI handles production image builds and pushes — see CI/CD and release process.

Relationship to CI/CD

The Dockerfile's ARG values and the README version table are the two places that must stay in sync during a release. The CI/CD workflow reads the Dockerfile as-is and publishes the resulting image under both latest and the git tag name.