GraalVM is an open source, high-performance, polyglot virtual machine developed by Oracle Labs. GraalVM offers multiple features, including the ability to compile Java code ahead-of-time into a native executable binary. The binary can run natively on the operating system, without a Java runtime

A native executable offers important benefits, like shorter startup time and lower memory footprint. In addition, when a native executable runs within a container, the size of the container image is reduced (when compared with the same Java application running in a traditional JVM), because the container image doesn’t include a Java runtime. An optimized container size is critical for deploying apps to the cloud.

We are pleased to announce that, starting with version 1.0.3, Helidon supports the GraalVM native-image capability. Now you can easily compile your Helidon application into a native executable with all the advantages described earlier. For example, the sample application described in this article has a startup time measured in tens of milliseconds and a MacOS executable size of only 21MB. Both of those numbers are higher when a traditional JVM is used.

On the other hand, everything is always a tradeoff. Long running applications on traditional JVMs are still demonstrating better performance than GraalVM native executables due to runtime optimization. The key word here is long-running; for short-running applications like serverless functions native executables have a performance advantage. So, you need to decide yourself between fast startup time and small size (and the additional step of building the native executable) versus better performance for long-running applications.

Compiling to native binaries introduces certain restrictions for your application. Because of native compilation, you must identify all the points in your code where reflection is used, which is not possible if CDI runtime injection is used. Helidon MP supports MicroProfile standards, which require CDI 2.0. Also, Helidon CDI cloud extensions are implemented as CDI plugins. We didn’t want to limit or complicate the user experience with Helidon MP; so GraalVM is supported in only Helidon SE. It is a perfect fit, because Helidon SE is designed to build small, reactive microservices. It doesn’t use dependency injection, annotations and other such magic . All the Helidon SE features and components (WebServer, Config, Security, Metrics, and Health Checks) are compatible with GraalVM native images.

Helidon supports two convenient GraalVM profiles:

• The local profile is for users who have GraalVM installed locally and want to build a native executable for the same OS that they work on.
• The Docker profile is for users who don’t have GraalVM installed locally or want to build native executable for Linux while using macOS locally.

Due to the possibility of backwards incompatible changes in GraalVM before the final release, the GraalVM support in Helidon is experimental. It’s been tested on GraalVM version RC13; it is not guaranteed to work on other GraalVM versions.

To get you started, Helidon has a quickstart sample, which you can use as a template for your Helidon-on-GraalVM application.

Generate the project using a Maven archetype:

mvn archetype:generate -DinteractiveMode=false \
    -DarchetypeGroupId=io.helidon.archetypes \
    -DarchetypeArtifactId=helidon-quickstart-se \
    -DarchetypeVersion=1.0.3 \
    -DgroupId=io.helidon.examples \
    -DartifactId=helidon-quickstart \
    -Dpackage=io.helidon.examples.quickstart

To build using the local profile you need to download GraalVM, extract it to some folder on your computer and define GRAALVM_HOME environment variable pointing to it.

If you use macOS, GRAALVM_HOME must point to Contents/Home directory inside the GraalVM root as it’s shown below.

export GRAALVM_HOME=~/graalvm-ce-1.0.0-rc13/Contents/Home

Build the project:

mvn package -Pnative-image

Run it:

./target/helidon-quickstart

If you want to use Docker profile, GraalVM installation is not required. Use the following command to build a docker image:

docker build -t helidon-native -f Dockerfile.native .

Run it as:

docker run --rm -p 8080:8080 helidon-native:latest

Helidon is a Java framework designed from scratch for writing microservices. It provides everything that you need to create small and efficient Java applications. It offers two programming models: reactive, and imperative supporting MicroProfile.

With GraalVM support, Helidon is one of the best solutions in the market for developing cloud-native microservices!

Do join our open-source community! We care about our users, and are ready to support you and answer your questions.

• Helidon on GitHub
• Helidon web site
• Helidon on Twitter
• Public Slack channel

Update

We tested it with newly released GraalVM RC16 (both CE and EE versions) and it perfectly works.