How to use Lambda layers

AwsHow-ToBeginner · 3 min read

How to Use AWS Lambda Layers: Syntax, Example, and Tips

Use Lambda layers to package and share libraries or code across multiple Lambda functions. Create a layer ZIP archive, publish it in AWS Lambda, then add the layer to your function's configuration to access its content during execution.

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Syntax

A Lambda layer is created by packaging your code or libraries into a ZIP file and publishing it as a layer version. Then, you add the layer to your Lambda function configuration using the Layers property. This makes the layer's content available in the /opt directory during function runtime.

Layer ZIP file: Contains your shared code or libraries.
Publish Layer: Upload ZIP to AWS Lambda as a layer version.
Add Layer to Function: Reference the layer ARN in your function's Layers list.

bash

aws lambda publish-layer-version --layer-name my-layer --description "My shared code" --zip-file fileb://layer.zip --compatible-runtimes python3.9

aws lambda update-function-configuration --function-name my-function --layers arn:aws:lambda:region:account-id:layer:my-layer:1

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Example

This example shows how to create a Lambda layer with a Python library, publish it, and use it in a Lambda function.

bash and python

mkdir python
pip install requests -t python/
zip -r layer.zip python

aws lambda publish-layer-version --layer-name requests-layer --description "Requests library" --zip-file fileb://layer.zip --compatible-runtimes python3.9

# Update your Lambda function to use the layer
aws lambda update-function-configuration --function-name my-function --layers arn:aws:lambda:region:account-id:layer:requests-layer:1

# Lambda function code example (handler.py):
import requests

def lambda_handler(event, context):
    response = requests.get('https://example.com')
    return {'statusCode': response.status_code, 'body': response.text[:100]}

Output

{"statusCode": 200, "body": "<!doctype html><html>..."}

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Common Pitfalls

Not packaging the layer content in the correct folder structure (e.g., Python libraries must be inside a python/ folder).
Forgetting to specify compatible runtimes when publishing the layer.
Not updating the Lambda function configuration to include the new layer version ARN.
Using layers that exceed the size limit (50 MB compressed).
Trying to use layers with incompatible runtimes or architectures.

bash

## Wrong: Packaging Python files at root instead of inside 'python/' folder
zip -r layer.zip mylib.py

## Right: Packaging inside 'python/' folder
mkdir python
mv mylib.py python/
zip -r layer.zip python

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Quick Reference

Package shared code in a ZIP file with correct folder structure.
Publish the ZIP as a Lambda layer with compatible runtimes.
Add the layer ARN to your Lambda function configuration.
Access layer content in /opt during function execution.
Keep layer size under 50 MB compressed.

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Key Takeaways

Package shared code in a ZIP file with the correct folder structure before publishing as a layer.

Publish Lambda layers specifying compatible runtimes to ensure function compatibility.

Add the layer ARN to your Lambda function configuration to use the layer content.

Access layer files inside the function at the /opt directory during runtime.

Avoid common mistakes like wrong folder structure or missing layer updates in function config.