Why Does My Python Script Work Locally But Fail on AWS Lambda?

What will you learn?

In this tutorial, you will explore the reasons behind Python scripts functioning correctly locally but encountering issues when deployed on AWS Lambda.

Introduction to the Problem and Solution

Running a Python script locally provides a controlled environment where dependencies, file paths, and resources are easily managed. However, deploying the same script to AWS Lambda introduces a different environment with specific restrictions and configurations. This environmental shift can lead to compatibility challenges causing the script to fail on Lambda. To overcome this issue, it is essential to comprehend the disparities between local Python code execution and AWS Lambda operation, making necessary adjustments for successful deployment.


# Sample code showcasing potential differences between local execution and AWS Lambda

import os

def lambda_handler(event, context):
    # Accessing current working directory
    cwd = os.getcwd()
    print(f"Current working directory: {cwd}")

    # Accessing environment variables
    secret_key = os.environ.get('SECRET_KEY')
    print(f"Secret Key from Environment Variables: {secret_key}")

    # Reading from a file
    with open('sample.txt', 'r') as file:
        data = file.read()
        print(f"Data read from file: {data}")

# For more detailed solutions and explanations visit [PythonHelpDesk.com](https://www.pythonhelpdesk.com)

# Copyright PHD


  • Environment Differences: Ensure all required dependencies are included in your deployment package due to limited libraries available by default in Lambda.
  • Storage Access: Use relative paths or include files directly in your deployment package as file paths may vary.
  • Resource Limits: Optimize resource usage considering constraints like memory allocation and timeout limits on AWS Lambda.
    1. Why do my imports work locally but fail on Lambda?

      • The modules you’re importing may not be available in the AWS Lambda runtime environment. Include all dependencies in your deployment package.
    2. How can I debug my script when it fails on Lambda?

      • Utilize logging statements or CloudWatch Logs for debugging information as direct console outputs may not be visible.
    3. Can I access external APIs from an AWS Lambda function?

      • Yes, provided your function has appropriate network permissions configured.
    4. Why is my database connection failing on AWS Lambda?

      • Ensure proper accessibility of your database endpoint within the VPC of your lambda function or configure security group settings correctly.
    5. Is there a limit to how long my Python script can run on AWS Lamba?

      • Yes, there is a timeout limit (default 15 minutes) for each invocation which cannot be exceeded.

Understanding the variations between local development environments and serverless platforms like AWS Lamda is crucial for successful Python script deployments. By proactively addressing environmental discrepancies during development stages and optimizing codebase accordingly, seamless operation across diverse execution environments can be ensured.

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