Working with layers for Node.js Lambda functions

A Lambda layer is a .zip file archive that contains supplementary code or data. Layers usually contain library dependencies, a custom runtime, or configuration files. Creating a layer involves three general steps:

This topic contains steps and guidance on how to properly package and create a Node.js Lambda layer with external library dependencies.

Prerequisites

To follow the steps in this section, you must have the following:

Throughout this topic, we reference the layer-nodejs sample application in the aws-lambda-developer-guide GitHub repository. This application contains scripts that download a dependency and package it into a layer. The application also contains corresponding functions that use the dependency from the layer. After creating a layer, you can deploy and invoke the corresponding function to verify that everything works. This sample application uses the Node.js 20 runtime. If you add additional dependencies to your layer, they must be compatible with Node.js 20.

The layer-nodejs sample application will package the lodash library into a Lambda layer. The layer directory contains the scripts to generate the layer. The function directory contains a sample function to test that the layer works. This document walks through how to create, package, deploy and test this layer.

Node.js layer compatibility with the Lambda runtime environment

When you package code in a Node.js layer, you specify the Lambda runtime environments that the code is compatible with. To assess code compatibility with a runtime, consider what versions of Node.js, what operating systems, and what instruction set architectures the code is designed for.

Lambda Node.js runtimes specify their Node.js version and operating system. In this document, you will use the Node.js 20 runtime, which is based on AL2023. For more information about runtime versions, see Supported runtimes. When you create a Lambda function, you specify the instruction set architecture. In this document, you will use the arm64 architecture. For more information about architectures in Lambda, see Selecting and configuring an instruction set architecture for your Lambda function.

When you use code provided in a package, each package maintainer independently defines their compatibility. Most Node.js development is designed to work independently of operating system and instruction set architecture. Additionally, breaking incompatibilities with new Node.js versions are not that common. Expect to spend more of your time assessing compatibility between packages than assessing package compatibility with Node.js version, operating system, or instruction set architecture.

Sometimes Node.js packages include compiled code, which require you to consider operating system and instruction set architecture compatibility. If you do need to assess code compatibility for your packages, you will need to inspect the packages and their documentation. Packages in NPM can specify their compatibility through the engines, os, and cpu fields of their package.json manifest file. For more information about package.json files, see package.json in the NPM documentation.

Layer paths for Node.js runtimes

When you add a layer to a function, Lambda loads the layer content into the execution environment. If your layer packages dependencies in specific folder paths, the Node.js execution environment will recognize the modules, and you can reference the modules from your function code.

To ensure that your modules are picked up, package them into your layer .zip file in one of the following folder paths. These files are stored in /opt, and the folder paths are loaded into the PATH environment variable.

For example, the resulting layer .zip file that you create in this tutorial has the following directory structure:

layer_content.zip
└ nodejs
    └ node20
        └ node_modules
            └ lodash
            └ <other potential dependencies>
            └ ...

You will put the lodash library in the nodejs/node20/node_modules directory. This ensures that Lambda can locate the library during function invocations.

Packaging the layer content

In this example, you package the lodash library in a layer .zip file. Complete the following steps to install and package the layer content.

Creating the layer

Take the layer_content.zip file that you generated in the previous section and upload it as a Lambda layer. You can upload a layer using the AWS Management Console or the Lambda API via the AWS Command Line Interface (AWS CLI). When you upload your layer .zip file, in the following PublishLayerVersion AWS CLI command, specify nodejs20.x as the compatible runtime and arm64 as the compatible architecture.

aws lambda publish-layer-version --layer-name node-lodash-layer \
    --zip-file fileb://layer_content.zip \
    --compatible-runtimes nodejs20.x \
    --compatible-architectures "arm64"

From the response, note the LayerVersionArn, which looks like arn:aws:lambda:us-east-1:123456789012:layer:node-lodash-layer:1. You'll need this Amazon Resource Name (ARN) in the next step of this tutorial, when you add the layer to your function.

Adding the layer to your function

Deploy a sample Lambda function that uses the lodash library in its function code, then attach the layer you created. To deploy the function, you need an execution role. For more information, see Defining Lambda function permissions with an execution role. If you don't have an existing execution role, follow the steps in the collapsible section. Otherwise, skip to the next section to deploy the function.

The sample function code uses the lodash _.findLastIndex method to read through an array of objects. It compares the objects against a criteria to find the index of a match. Then, it returns the index and value of the object in the Lambda response.

import _ from "lodash"

export const handler = async (event) => {

  var users = [
  { 'user': 'Carlos',  'active': true },
  { 'user': 'Gil-dong',    'active': false },
  { 'user': 'Pat', 'active': false }
  ];

  let out = _.findLastIndex(users, function(o) { return o.user == 'Pat'; });
  const response = {
    statusCode: 200,
    body: JSON.stringify(out + ", " + users[out].user),
  };
  return response;
};