AWS Lambda Java 21 Custom Runtime

An AWS Lambda layer to enable Java 21 support.

Usage

In AWS Console

• Download java21layer.zip
• Upload to S3 (required to create a layer from a ZIP file greater than 50MB in size)
• In Lambda console, create a layer using this ZIP file using the x86_64 architecture and the Custom runtime on Amazon Linux 2 runtime
• In Lambda console, create a function with Provide your own bootstrap on Amazon Linux 2 and architecture x86_64
• In Lambda function console, add the layer you created, and upload your Java deployment package
• Run
• (Hopefully) celebrate! 🥳

with CDK

• Download java21layer.zip
• Create a Lambda layer using Code.fromAsset java21layer.zip
• Note you might need to adjust the path for your own project structure

LayerVersion java21layer = new LayerVersion(this, "Java21Layer", LayerVersionProps.builder()
        .layerVersionName("Java21Layer")
        .description("Java 21")
        .compatibleRuntimes(Arrays.asList(Runtime.PROVIDED_AL2))
        .code(Code.fromAsset("java21layer.zip"))
        .build());

• Create a function using the PROVIDED_AL2 runtime.
• Add this layer to your function.

Function exampleWithLayer = new Function(this, "ExampleWithLayer", FunctionProps.builder()
        .functionName("example-with-layer")
        .description("example-with-layer")
        .handler("example.HelloWorld::handleRequest")
        .runtime(Runtime.PROVIDED_AL2)
        .code(Code.fromAsset("../software/ExampleFunction/target/example.jar"))
        .memorySize(512)
        .logRetention(RetentionDays.ONE_WEEK)
        .layers(singletonList(java21layer))
        .build());

Layer Details

Java 21

A custom JRE is created to reduce final file size. Lambda has a 250MB unzipped file size limit.

Dockerfile describes how the JRE is built.

Known Issues

Obviously, it's early days, and this is a preliminary release. There are a couple of known issues:

1. The layer fails CDS (Class Data Sharing) during initialization. This creates some log traffic, and may adversely affect performance.
2. It is only (lightly) tested
3. Only x86_64 is supported

I'll be working on these as I have time. PRs welcome!

JVM Settings

The following JVM settings are added by default.

--add-opens java.base/java.util=ALL-UNNAMED 
-XX:+TieredCompilation -XX:TieredStopAtLevel=1 
-Xshare:auto

Further suggestions welcomed

Java Class Path

aws-lambda-java-core-1.2.3.jar
aws-lambda-java-serialization-1.1.2.jar
aws-lambda-java-runtime-interface-client-2.4.1.jar
$LAMBDA_TASK_ROOT
$LAMBDA_TASK_ROOT/*
$LAMBDA_TASK_ROOT/lib/*

Build the layer zip yourself

Requirements

• Docker

Steps

• Run build-jre.sh to build the minimal Java 21 runtime
• Run make-layer.sh to package the runtime, dependencies and bootstrap as a zip

Acknowledgements

Much credit to @msailes, who created the original repo from which this project is forked!