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.

Based on the official BusyBox glibc image

Based on the official Alpine image and Alpine GLIBC package

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