How to Create a Python Lambda Layer Using AWS CDK

Discover how to easily create a custom Python Lambda layer using AWS CDK with step-by-step guidance for seamless integration.
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How to Create a Python Lambda Layer Using AWS CDK

As developers using AWS Lambda, we often find ourselves needing to share common code across multiple functions. AWS Lambda layers provide a convenient way to encapsulate such shared functionality. However, creating a custom Lambda layer using the AWS Cloud Development Kit (CDK) can be tricky, especially if you're new to this ecosystem. If you’ve attempted to set up a Python Lambda layer with CDK, you might have encountered challenges related to folder structures and package imports. In this post, we will provide a clear, step-by-step guide on how to successfully create and utilize a Lambda layer for the Python runtime.

The Challenge: Setting Up the Lambda Layer

We will tackle a common issue that many developers face: importing shared functions from a Lambda layer. Here’s what typically happens when you try to create a custom layer:

You define a Layer in CDK.

You set the Lambda function to utilize this layer.

However, you encounter an error indicating that the module cannot be found when invoking the function. For example:

[[See Video to Reveal this Text or Code Snippet]]

In our scenario, the structure of the layer folder was not set up correctly, leading to this error message.

The Solution: Proper Folder Structure for Lambda Layers

To resolve the issue, we need to adjust our folder structure. Here’s a breakdown of the steps required to set up a Python Lambda layer correctly using AWS CDK:

Step 1: Define the Lambda Layer in Your Code

First, you’ll need to create a shared layer within your CDK application. Here’s an example of how to define it in your CDK code using JavaScript:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Create the Function That Uses the Layer

You also need to define a Lambda function that will utilize your shared layer. Here’s how it looks:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Set the Correct Folder Structure for the Layer

The critical step involves ensuring the layer's folder structure is set properly. Instead of placing your shared code directly inside the shared-layer folder, you need to create a subfolder named python within your shared layer. Here's the recommended structure:

[[See Video to Reveal this Text or Code Snippet]]

Why the 'python' subfolder?

AWS Lambda requires libraries and Python files to be stored within a folder named python to recognize and load them correctly when the layer is invoked.

Step 4: Combine and Test Locally

Once you’ve defined your layer properly, you can generate the CloudFormation template using:

[[See Video to Reveal this Text or Code Snippet]]

To ensure that everything works correctly, test your Lambda function locally using the Serverless Application Model (SAM):

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By following these steps, you should be able to create a custom Lambda layer using AWS CDK successfully. Remember that the key takeaway is the importance of proper folder structure. Always make sure to encapsulate your Python shared functions under the python subfolder within your layer. This small adjustment can save you a lot of headaches related to module import errors!

Feel free to reach out with any questions or share your experiences regarding the use of AWS Lambda layers!