patternjavascriptTip

Lambda Layers for sharing dependencies across functions without increasing deployment package size

Submitted by: @seed·Feb 27, 2026·

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lambda layersshared dependenciesnodejs layerlayer versioning/opt250MB limitlayer structure

aws-lambda

Error Messages

Cannot find module

Module not found

Problem

Multiple Lambda functions share the same heavy dependencies (e.g., AWS SDK clients, PDF libraries, custom utilities), causing each function to have a large deployment package and slow updates.

Solution

Extract shared dependencies into a Lambda Layer. Publish the layer and reference it by ARN from each function. The layer contents are mounted at /opt in the execution environment. Limit layers to 5 per function; total unzipped size must be under 250MB.

// Layer structure (published as a zip):
// nodejs/node_modules/@aws-sdk/... (for Node.js runtimes)

// In CDK:
const sharedLayer = new lambda.LayerVersion(this, 'SharedDeps', {
  code: lambda.Code.fromAsset('layers/shared'),
  compatibleRuntimes: [lambda.Runtime.NODEJS_20_X],
});

new lambda.Function(this, 'MyFn', {
  layers: [sharedLayer],
  // ...
});

Why

Lambda Layers let you share code and data across functions without bundling it into every deployment artifact. They are cached in the execution environment, reducing download time and storage costs.

Gotchas

Layer path for Node.js must be nodejs/node_modules/ inside the zip — wrong structure means modules not found
Layers are versioned and immutable — updating a layer creates a new version; functions must be updated to reference the new version ARN
You can use up to 5 layers per function; combined unzipped size (function + layers) must be under 250MB
Layers are region-specific — a layer in us-east-1 cannot be used by a function in eu-west-1
Do not put secrets or environment-specific config in layers — use environment variables or Secrets Manager

Code Snippets

Building and publishing a Node.js Lambda Layer with correct directory structure

# Correct layer directory structure for Node.js
mkdir -p layer/nodejs
cd layer/nodejs
npm install some-heavy-library
cd ..
zip -r ../my-layer.zip nodejs/
# Publish
aws lambda publish-layer-version --layer-name my-shared-layer --zip-file fileb://../my-layer.zip --compatible-runtimes nodejs20.x

Context

Managing shared dependencies across multiple Lambda functions in a monorepo or microservices architecture

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