AWS Lambda is a powerful serverless computing service that allows you to run code without provisioning or managing servers. However, running Python code on AWS Lambda can sometimes lead to module import errors, such as the infamous “No module named psycopg2.” This article will explore the reasons behind this error and provide approaches to resolve it, including relevant code snippets.

What is ‘No Module Named psycopg2’ in AWS Lambda?

The error “No module named psycopg2” in AWS Lambda occurs when the Lambda function is unable to locate the psycopg2 library, which is essential for interacting with PostgreSQL databases from Python code. This error often stems from the differences in the Lambda execution environment compared to local development environments.

Three Reasons for ‘No Module Named psycopg2’ in AWS Lambda Error

1. Missing psycopg2 Library in Deployment Package

Reason: The deployment package does not include the psycopg2 library. This typically happens when the library is not installed in the Lambda function’s deployment package.

{
  "errorMessage": "Unable to import module 'lambda_function': No module named 'psycopg2'"
}

2. Platform-Specific Binary Incompatibility

Reason: The psycopg2 library installed on your local machine may not be compatible with the Lambda execution environment, which uses Amazon Linux. Binary dependencies must match the Lambda environment.

{
  "errorMessage": "Unable to import module 'lambda_function': No module named 'psycopg2'"
}

3. Incorrect Lambda Layer Configuration

Reason: The psycopg2 library might be placed in a Lambda Layer, but the Layer is not correctly attached to the Lambda function or does not contain the library in the expected path.

{
  "errorMessage": "Unable to import module 'lambda_function': No module named 'psycopg2'"
}

Approaches to Solve with Correct Code

Approach 1: Including psycopg2 in Deployment Package

Create a Deployment Package:

• Install psycopg2-binary in a directory.
• Zip the directory along with your Lambda function code

mkdir package
pip install psycopg2-binary -t package/
cd package
zip -r ../my-deployment-package.zip .
cd ..
zip -g my-deployment-package.zip lambda_function.py

Upload the Deployment Package to AWS Lambda:

• Go to the AWS Lambda console.
• Create a new function or select an existing one.
• Upload the my-deployment-package.zip.

Approach 2: Using Lambda Layers

Create a Lambda Layer with psycopg2:

• Create a directory structure for the Lambda Layer.

mkdir -p python/lib/python3.9/site-packages
pip install psycopg2-binary -t python/lib/python3.9/site-packages/
zip -r psycopg2-layer.zip python

Deploy the Lambda Layer:

• Go to the AWS Lambda console.
• Create a new layer and upload the psycopg2-layer.zip.

Attach the Layer to Your Lambda Function:

• Go to your Lambda function.
• Under the “Layers” section, add the newly created layer.

Approach 3: Building psycopg2 for Amazon Linux

Build psycopg2 on an Amazon Linux Environment:

• Use an Amazon Linux Docker container to build psycopg2.

docker run -it amazonlinux:2
yum install -y python3-devel postgresql-devel gcc
pip3 install psycopg2-binary -t /path/to/your/lambda/package

Create and Upload the Deployment Package:

• Zip the contents of /path/to/your/lambda/package and your Lambda function code.
• Upload it to the AWS Lambda console as described in Approach 1.

Conclusion

The “No module named psycopg2” error in AWS Lambda can be a stumbling block when working with PostgreSQL databases. By understanding the underlying reasons and following the provided approaches, you can effectively resolve this issue and ensure your Lambda functions can interact with PostgreSQL seamlessly. Whether you choose to include the library in your deployment package, use Lambda Layers, or build the library for Amazon Linux, these solutions will help you overcome this common obstacle.