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Java 16 EA Alpine & JLink vs Graal

My first post... hurrah!

As the saying goes: good things come in small packages. For container images it means a smaller attack surface and faster to deploy and start-up. Unfortunately, Java hasn't been the best candidate for containerisation but that has changed with a few interesting developments:

With Java 16 we can now use JLink with Alpine images to get all the next gen GCs (a-la ZGC and Shenandoah) goodness.

I thought it would be useful to compare and contrast them with a simple ReST service. For this I'm using io.helidon.archetypes:helidon-quickstart-mp:2.2.0 archetype as a base with some customisations to the Dockerfiles.

ℹ️ This is a Microprofile implementation so that means full-fat CDI, JAX-RS goodness which IMHO gives a good compromise between standards, developer productivity and scalability.

There were some changes required to the files.

For Dockerfile:

-FROM openjdk:11-jre-slim
+FROM openjdk:16-jdk-alpine
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For Dockerfile.jlink:

-FROM maven:3.6.3-jdk-11-slim as build
+FROM openjdk:16-jdk-alpine as build
+RUN apk add --no-cache bash maven

-FROM debian:stretch-slim
+FROM alpine:3.13.0
+RUN apk add --no-cache bash
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ℹ️ We must add bash to the Alpine JLink image which adds 2MB as Helidon is using a little script to start up. Ideally if productionising this I would aim to remove this dependency.

So, what do the images sizes look like using the Slim JDK image as a control:

Image Size Change
JDK 11 Slim (Debian) 220MB 100%
Alpine 338MB 154%
Alpine JLink 127MB 58%
Graal native image 94MB 43%

As expected Graal based on scratch image is very small followed by Alpine JLink, Slim and finally Alpine at the rear. Now for start up time:

Image Time Change
JDK 11 Slim (Debian) 4,493ms 100%
Alpine 3,310ms 74%
Alpine JLink 1,844ms 41%
Graal native image 80ms 2%

Again, not many surprises here except Graal is faster than I thought!


It's a very interesting time for Java and containers. Java can be lean, light and fast which still makes it relevant in a container native deployment.

Both JLink (gRPC#3522) and Graal have some issues; I'm especially concerned about the Serial GC in Graal so will be putting that under some stress soon to see if that confirms my suspicions. I'll also be good when some Java 16 JRE Alpine images appear as the JDK is too bloaty.

Jury is out if Graal or JLink is my preferred approach until I can stick load on them and see how they behave in Kubernetes but things are looking good.

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