Helidon SE: use jlink to create minimal Java 11 runtime

[barchetta]

Environment Details

• Helidon Version: 0.10.4
• Helidon SE
• JDK version: 11

Problem Description

We should determine the minimum set of modules needed to run a Helidon SE application and document it. Also, we should consider updating our quickstart Dockerfile to generate the JRE as part of a two stage docker build.

I did a quick experimentation and this seems to work, but I did not exercise very many code paths:

$JAVA_HOME/bin/jlink --compress=2 --output jre --add-modules java.base,java.logging,java.sql,java.desktop,java.management

[barchetta]

Here are some examples of dependencies on modules of interest:

java.desktop: java/beans/IntrospectionException (org.yaml.snakeyaml)
java.sql: java/sql/Date (org.yaml.snakeyaml)
java.management: java/lang/management/ManagementFactory (io.helidon.metrics.BaseRegistry)

[barchetta]

Example Dockerfile to generate image with custom JRE:

# Multistage docker build.
# Stage 1: Build custom Java 11 JRE and put it in /var/tmp/myjre
FROM openjdk:11-slim AS build
RUN ["jlink", "--compress=2", \
     "--add-modules", "java.base,java.logging,java.sql,java.desktop,java.management", \
     "--output", "/var/tmp/myjre"]

# Stage 2: Build application image using JRE from Stage 1
FROM debian:sid-slim
COPY --from=build /var/tmp/myjre /opt/jre
ENV PATH=$PATH:/opt/jre/bin

RUN mkdir /app
COPY libs /app/libs
COPY ${project.artifactId}.jar /app

CMD ["java", "-jar", "/app/${project.artifactId}.jar"]

[ljnelson]

Yep; more stuff than you think pulls in java.desktop for the Java beans features.

Haven’t thought deeply about this but if we put together some kind of configuration in the sample app that does not use YAML etc. we might be able to use requires static or something similar to sever a branch off the dependency tree.

[barchetta]

Ack! Because of bug docker-library/openjdk#217 the above approach results in a docker image size >500MB. Need to look for a work-around.

[barchetta]

The work-around for the bloated libjvm.so is to strip it. Ick:

RUN [ "apt", "update"]
RUN [ "apt-get", "install", "-y", "binutils"]
RUN ["strip", "-p", "--strip-unneeded", "/var/tmp/myjre/lib/server/libjvm.so"]

[barchetta]

This is being documented in PR #182