How to Fix Psycopg2 ‘ModuleNotFoundError’:Using AWS Lambda-Layer

Introduction

The psycopg2 module is a PostgreSQL adapter for Python, which is commonly used in applications requiring database interactions. However, when deploying such applications to AWS Lambda, the module must be packaged as a Lambda layer due to Lambda’s isolated environment. This involves creating a virtual environment, installing psycopg2-binary, and zipping the site-packages directory to create the layer. Once uploaded to AWS, this layer can be attached to Lambda functions, ensuring that psycopg2 is available during execution.

What is Python Code Error: No Module Named ‘psycopg2’
When you try to run a Python script in AWS Lambda, it might not find certain libraries like psycopg2, even if they’re installed on your computer. This happens because AWS Lambda runs in a different environment than your local machine. To fix this, you need to package these libraries into something called a “Lambda layer” and attach it to your Lambda function. Think of a Lambda layer like a special package that includes all the extra tools your script needs to work properly.

Resolving the psycopg2 Module Error in AWS Lambda

Even if it's installed in your local IDE. This error occurs because AWS Lambda requires a specific environment setup for dependencies, which differs from your local development environment.

Understanding the Error

The psycopg2 module is a PostgreSQL database adapter for Python. When you install it locally using pip, it works fine in your IDE. However, AWS Lambda has its own environment and dependencies must be packaged differently.

Why psycopg2 Isn’t Found in Lambda

1. Local Installation vs. Lambda Environment: When you install psycopg2 locally, it’s installed in your system’s Python environment. AWS Lambda, however, runs in a separate environment (Amazon Linux) and doesn’t access your local Python environment.

2. Dependency Packaging: AWS Lambda requires that all dependencies be included in the deployment package. If psycopg2 isn’t properly packaged, it won’t be available in the Lambda environment.

Step 1: Guide to Creating a psycopg2 Lambda Layer
To resolve this issue, we are going to create a Lambda layer for psycopg2.

Create a Directory for the Layer:

mkdir psycopg2_layer
cd psycopg2_layer

Create a Virtual Environment:
Ensure using a compatible Python version (e.g., Python 3.9).

python3 -m venv env
source env/bin/activate

Install psycopg2-binary in the Virtual Environment:

Upgrade pip inside the virtual environment.

pip install --upgrade pip

Install psycopg2-binary:

pip install psycopg2-binary

Package psycopg2 as a Lambda Layer: Create a directory for the Lambda layer.

mkdir python
cp -r env/lib/python3.*/site-packages/* python/

Zip the directory:

zip -r psycopg2_layer.zip python/

Mac Terminal & VScode views:

Step 2: Create a Lambda Layer in AWS

1. Go to the AWS Lambda console.
2. Navigate to the “Layers” section.
3. Click “Create layer”: Name- psycopg2-layer
4. Description: PostgreSQL-adapter
5. Choose “Upload a .zip file” and select the psycopg2_layer.zip file.
6. Set the runtime to match your Lambda function’s runtime Python 3.9.

Step 3: Attach the Layer to Your Lambda Function

1. Open your Lambda function in the AWS console.
2. Go to the “Layers” section.
3. Click “Add a layer” and select the psycopg2 layer you created.

Conclusion

By following these steps, you can successfully resolve the psycopg2 “ModuleNotFoundError” in AWS Lambda by creating and using a Lambda layer. This approach ensures that your application has access to all necessary dependencies in the Lambda environment.

Share Your Thoughts

Have you encountered similar issues with AWS Lambda? How did you resolve them? Share your experiences in the comments below!