xfournet/jready repository overview

⁠JRE ready Docker image

jready is a set of minimalist Docker images⁠ that are ready to execute a JRE.

More than a small size, the goal of minimal Docker image is to enhance security by reducing the attack surface.

Note than these images don't include a JRE:

• you can freely choose the JRE vendor (e.g. Oracle or OpenJDK) and version (tested from 1.7 to 15)
• with JRE 9 and higher, you can freely build your own minimal JRE thanks to jlink⁠. See example below.

An example below shows how a JRE can be integrated on top of these images.

⁠BusyBox based (busybox/Dockerfile)⁠

Based on the official BusyBox glibc image⁠

⁠Alpine based (alpine/Dockerfile)⁠

Based on the official Alpine image⁠ and Alpine GLIBC package⁠

⁠Example

This example is using AdoptOpenJDK 15. It's based from the busybox based image but alpine can be used instead with no other changes in the Dockerfile.

Dockerfile

Create a minimal JRE image. If needed the JLINK_MODULES list (comma-separated) can be completed to fit other needs.

FROM xfournet/jready:busybox

ARG JDK_URL=https://github.com/AdoptOpenJDK/openjdk15-binaries/releases/download/jdk-15%2B36/OpenJDK15U-jdk_x64_linux_hotspot_15_36.tar.gz
ARG JLINK_OPTIONS="--vm=server --compress=2 --no-header-files --no-man-pages"
ARG JLINK_MODULES="java.base"
ARG JRE_DIR="/opt/jre"

RUN \
    # Download and extract JDK
    wget ${JDK_URL} -O - | tar xz -C /tmp && \
    # Build customized JRE
    /tmp/jdk-*/bin/jlink --output ${JRE_DIR} --add-modules ${JLINK_MODULES} ${JLINK_OPTIONS} && \
    # Remove JDK
    rm -r /tmp/jdk-* 
    
ENV PATH="${JRE_DIR}/bin:${PATH}"    

Image build and test

docker build -t myjre .
docker run --rm -ti myjre

# in container
java --version