Demo for a minimalized Java Container

Goal is:

Build a minimalized Java Container, which can run in an internet connected and a disconnected environment. The complete build is made in a single "docker build" run, though it's not required to have a local JDK installation or a pipelining tool like Jenkins, gitlab, ...

The resulting image has nearly nothing unused installed.

Size comparison:

• the build container has (on Arm64) a size of 1.42GB
• the resulting run container has (also on Arm64) a size of 215MB

We're using a 2 phase build:

• Phase 1:

  • Build artefacts with maven
  • Generate a minimal JRE runtime with jlink

• Phase 2:

  • Copy the minimal JRE runtime and the artefacts in an UBI9 minimal container

All builds can be made in an OpenShift / OKD cluster as BuildConfigs, with ShipWirght or with podman / podman-desktop or docker.

Connected build

Your build environment has internet access (can reach the redhat container registry and maven central).

# Java 17
podman build \
  -t reg.pflaeging.net/public/minijavacontainer:latest \
  --env JAVA_VERSION=17 \
  .
# Java 21
podman build \
  -t reg.pflaeging.net/public/minijavacontainer:latest \
  --env JAVA_VERSION=21 \
  .

Disconnected build

Your in an intranet and your build infrastructure has its own registry for base images and a maven central mirror (you should also have an RPM repo mirror and the base images configured to use it).

# Java 17
podman build \
  -t reg.pflaeging.net/public/minijavacontainer:latest \
  --build-arg BASE_IMAGE=registry.internal.pflaeging.net/ubi9-minimal:9.4 \
  --env JAVA_VERSION=17 \
  --env MAVEN_REPO_MIRROR=https://centralrepo.myorg.net/artifactory/mirror-maven \
  .
# Java 21
podman build \
  -t reg.pflaeging.net/public/minijavacontainer:latest \
  --build-arg BASE_IMAGE=registry.internal.pflaeging.net/ubi9-minimal:9.4 \
  --env JAVA_VERSION=21 \
  --env MAVEN_REPO_MIRROR=https://centralrepo.myorg.net/artifactory/mirror-maven \
  .

Openshift BuildConfig

A sample BuildConfig for OpenShift / OKD is added as ./BuildConfig.yaml. This is only an example. Adopt it to your settings

Execute

To test this container if it'S running simply start it :-):

podman run -ti reg.pflaeging.net/public/minijavacontainer:latest

Multi-architecture build

For all of us using a MacBook with Apple M processor and deploying in an AMD64 / Intel64 structure:

Make a multi-arch build:

• Install on Mac:
  • podman-desktop
  • podman

Build a multi-arch image:

# create a manifest for a multi-arch container
podman manifest create \
  reg.pflaeging.net/public/minijavacontainer:multiarch-latest
# build for both architectures and link it to the manifest
podman build --platform linux/amd64 \
  -t localhost/minijavacontainer:amd64-latest \
  --env JAVA_VERSION=17 .
podman build --platform linux/aarch64 \
  -t localhost/minijavacontainer:aarch64-latest \
  --env JAVA_VERSION=17 .
# link to manifest
podman manifest add \
  reg.pflaeging.net/public/minijavacontainer:multiarch-latest \
  localhost/minijavacontainer:amd64-latest
podman manifest add \
  reg.pflaeging.net/public/minijavacontainer:multiarch-latest \
  localhost/minijavacontainer:aarch64-latest
# push the result to the registry
podman manifest push \
  reg.pflaeging.net/public/minijavacontainer:multiarch-latest \
  docker:reg.pflaeging.net/public/minijavacontainer:multiarch-latest