How to package AWS CDK into Lambda layer?

Question

What is the best way to bundle up the AWS CDK as a Lambda layer please?

I need to call the CDK from a Java process, so wish to use the Java 11 runtime and then install Nodejs and the CDK as 2 separate layers. Currently I download the Nodejs binaries and then use something like the following:

    LayerVersion nodeLayer = LayerVersion.Builder.create(this, "node-layer")
            .description("Layer containing Node.js")
            .code(
                    Code.fromAsset(somePathToNodejs)
            )
            .build();

then refer to the layer within the Lambda constructor / builder.

The CDK is installed as npm install -g aws-cdk, so I don't know how best to bundle this up in a similar fashion.

So you want to run npm install on a specific folder and upload the content as a layer? — Amit Baranes

John John · Accepted Answer · 2020-02-25T16:28:40

I ended up using a Docker container to install the aws-cdk module into a specific path, then zip up the container and copying it to a bind-mounted directory so that it is available on the underlying host.

I built the project using Gradle and the gradle-docker-plugin by Ben Muschko. I have not spent time trying to use a smaller Node image to speed up builds.

task createCdkDockerfile(type: Dockerfile) {
    from 'node:latest'
    defaultCommand('/bin/bash', '-c', "apt-get update && apt-get install -y zip && mkdir -p /nodejs && npm config set prefix /nodejs/bin && npm install -g aws-cdk && pushd /nodejs/bin && zip -r --symlinks /opt/aws-cdk.zip *")
}

task buildCdkImage(type:DockerBuildImage) {
    dependsOn createCdkDockerfile
    images.add('my-aws-cdk:latest')
}

ext.maybeConvertWindowsPath = { path ->
    if (Os.isFamily(Os.FAMILY_WINDOWS)) {
        path = "/${path.replace("\\", "/").replace(":", "")}"
    }
    return path
}

task createCdkContainer(type: DockerCreateContainer) {
    def dockerBindDir = new File(buildDir, "docker")
    dockerBindDir.mkdirs()
    dependsOn buildCdkImage
    targetImageId buildCdkImage.getImageId()
    hostConfig.autoRemove = true
    hostConfig.binds = ["${maybeConvertWindowsPath(buildDir.toString())}/docker" : "/opt"]
}

task startCdkContainer(type: DockerStartContainer) {
    dependsOn createCdkContainer
    targetContainerId createCdkContainer.getContainerId()
}

task waitCdkContainer(type: DockerWaitContainer) {
    dependsOn startCdkContainer
    targetContainerId createCdkContainer.getContainerId()
}

The zip file is available at ${buildDir}/docker/aws-cdk.zip.

Adding the CDK as a layer is as per the Nodejs example in my question, so something like this:

LayerVersion nodeLayer = LayerVersion.Builder.create(this, "aws-cdk-layer")
        .description("Layer containing AWS CDK")
        .code(
                Code.fromAsset(somePathTo-aws-cdk.zip)
        )
        .build();

Points to watch out for:

if building on Windows, zipping up on Windows then unzipping on Linux will give issues with files that should be executable no longer being executable, i.e. cdk itself.
bind mounting directories seems to have issues when on Windows, hence the need to sanitize the filename.
when zipping, it's important to use the --symlinks option, otherwise the cdk executable will not be able to find the cdk.js file.

I would have preferred using tar to zip the file up, but fromAsset() won't accept tar files.

How to package AWS CDK into Lambda layer?

1 Answers