Introduction to AWS Lambda with Python
AWS Lambda is a powerful service that allows developers to run code without provisioning or managing servers. This serverless computing service automatically scales your applications by running code that responds to events, making it ideal for microservices, data processing, and real-time file handling. Python is one of the most popular languages supported by AWS Lambda. It offers simplicity and extensive library support, making it a perfect match for writing Lambda functions.
Two Options for Writing Lambda Functions
When working with AWS Lambda and Python, there are two primary methods to write and deploy your functions:
- Option 1: Writing Functions in the AWS Editor
- Option 2: Writing and Uploading Zipped Functions
Option 1: Writing Functions in the AWS Editor
The AWS Management Console provides an in-browser editor where you can write and deploy your Lambda functions directly. This method is convenient for quick edits, testing small pieces of code, or when your function has minimal dependencies.
However, when your function relies on external libraries, more than the built-in editor may be required. In such cases, the second option—writing your function locally and uploading it as a zip file—becomes necessary.
Option 2: Writing and Uploading Zipped Functions
Uploading a zipped package is recommended for more complex Lambda functions requiring external libraries or advanced code management. This method allows you to develop and test your code locally before deploying it to AWS Lambda.
Detailed Instructions for Option 2: Uploading Zipped Functions
Let’s walk through the process of writing your Lambda function, managing external libraries, zipping the code, and uploading it to AWS Lambda.
1. Create and Write Your Lambda Function
Start by creating a new directory on your local machine where you’ll write your Lambda function. Within this directory, create a Python file (e.g., lambda_function.py) and define the function handler:
def lambda_handler(event, context):
return {
‘statusCode’: 200,
‘body’: ‘Hello, World!’
}
The function lambda_handler is the entry point for your Lambda function, where the event contains input data, and context provides runtime information.
2. Download and Manage External Libraries
If your Lambda function depends on external Python libraries, you’ll need to install them in the same directory as your function. For example, if your function requires the requests library, use pip to install it:
pip install requests -t .
This command installs the requests library and dependencies into the current directory, making them available for your Lambda function.
3. Zip Your Code and Libraries
Once your code and libraries are ready, you must compress them into a zip file. Ensure that all necessary files, including your Python script and the requests library directory, are included in the zip file.
zip -r lambda_function.zip .
This command zips all the contents of the current directory, creating a file named lambda_function.zip.
4. Upload the Zip File to AWS Lambda
To deploy your zipped function:
- Navigate to the AWS Lambda console.
- Create a new Lambda function or select an existing one.
- Under the “Function code” section, select “Upload a .zip file” as the code entry type.
- Upload your lambda_function.zip file.
- Set the handler name to lambda_function.lambda_handler.
Finally, save the changes to deploy your Lambda function.
Troubleshooting Common Errors with Zipped Functions
When working with zipped Lambda functions, you might encounter some common issues. Below are solutions to these problems.
Resolving the “lambda_function.lambda_handler cannot be found” Error
This error typically occurs when AWS Lambda cannot locate the handler function. Ensure that the file containing your function matches the handler name provided in the AWS Lambda console. For example, if your file is named lambda_function.py, your handler should be lambda_function.lambda_handler.
Understanding and Correcting File Structure Issues
AWS Lambda requires your code and dependencies to be at the root of the zip file. If you accidentally zip the entire project directory, you might have an extra folder level in your archive, causing Lambda to fail to locate your handler function. Double-check that all files are correctly placed at the top level of your zip file.
Ensuring the Correct Lambda Hierarchy
Ensure that your Lambda function follows this structure within the zip file:
– lambda_function.py
– requests/
– __init__.py
– …
Proper file hierarchy is crucial for the Lambda service to execute your code correctly.
Conclusion
Writing and running AWS Lambda functions with Python offers flexibility and power, especially when you leverage the ability to upload zipped functions. By following the steps outlined in this guide, you can efficiently develop, package, and deploy your Python-based Lambda functions, ensuring a smooth and error-free experience.