Introduction

In deploying Python Lambda functions on AWS, one might encounter an error that reads: "No module named requests." This error is a telltale sign that the function is attempting to import the `requests` library but it's unavailable in the Lambda execution environment. This article delves into what causes this issue, and how you can resolve it by deploying dependencies correctly with AWS Lambdas. Additionally, we will cover best practices for managing dependencies in AWS Lambda functions.

Understanding AWS Lambda Execution Environment

AWS Lambda allows you to run code without provisioning or managing servers. The underlying infrastructure is fully managed by AWS, which means:

• Lambda functions operate in a restrictive execution environment.
• Not all Python modules or packages are available by default.
• The size of the deployment package is a key consideration, with the unzipped deployment package size limit being 250 MB.

These constraints necessitate packaging any external modules or libraries with your Lambda functions.

The "No Module Named Requests" Error

What It Means

The error occurs because the `requests` library, a popular Python package for making HTTP requests, is not included in the AWS Lambda execution environment by default. To use this library, it must be installed and packaged with your function's deployment package.

Technical Explanation

When you use an `import` statement in your Python script, Python will look for the package in its current execution environment. For AWS Lambda, this means looking in the directories you've included in your deployment package plus any globally available directories.

If the requested module isn't found, Python raises the "No module named `requests`" error.

Solutions

Packaging Dependencies with AWS Lambda

1. Use a Requirements File:
   • Create a `requirements.txt` file that lists `requests`, along with any other dependencies.
   • Use a virtual environment to install packages listed in the `requirements.txt`.
   • Navigate to the virtual environment's `site-packages` directory and package your code with its dependencies.
   • You can upload this ZIP file when creating or updating your Lambda function in the AWS Management Console or via an AWS CLI command.
   • Package your dependencies in a suitable directory structure.
   • Use the AWS Management Console or CLI to create a Lambda Layer from this ZIP file.
   • Include the Layer in your Lambda function configuration either through the console UI or a command line.