lambda-warmer-py

What it is and what it does

lambda-warmer-py is a Python decorator that addresses AWS Lambda cold starts—the latency spike when a function is invoked after being idle. You wrap your Lambda handler with the decorator, then set up a CloudWatch rule to ping the function every 5 minutes with a special warming event. The decorator detects these warming invocations, executes them quickly without running your actual business logic, and keeps the Lambda container alive and ready.

The package supports concurrent warming (invoking multiple copies of your Lambda to keep several containers warm simultaneously) and optional CloudWatch metrics that track cold versus warm starts by function name. Configuration is minimal—you can customize the event field names, concurrency delay, and whether to send metrics—but the core behavior requires only the decorator and a scheduled ping.

Use it for:

• Reduce latency for user-facing Lambda APIs by keeping functions warm during off-peak hours or between infrequent requests.
• Monitor cold start frequency across your Lambda fleet by sending metrics to CloudWatch for alerting and optimization.
• Maintain multiple concurrent warm Lambda containers to handle sudden traffic spikes without cold start penalties.
• Optimize serverless applications where predictable response time is critical, such as real-time data processing or webhook handlers.

Worth the install?

AI-flagged interpretation of the facts on this page — verify before relying

A decorator that minimizes AWS Lambda cold starts by keeping functions warm through periodic invocations and optionally tracking cold/warm start metrics to CloudWatch.

No. The package is abandoned (last commit 2022-01-05, no releases since 2019-11-23) and offers no maintenance or support. While the core logic may still function, AWS Lambda and best practices have evolved significantly. Consider using modern alternatives or native AWS solutions that are actively maintained and better integrated with current Lambda capabilities.

Install

lambda-warmer-py on PyPI

pip install lambda-warmer-py

uv add lambda-warmer-py

poetry add lambda-warmer-py

Installing lambda-warmer-py

Before you install

Low install friction with no runtime dependencies. However, the package is abandoned—last commit was 2022-01-05 and no releases since 2019-11-23. While it may still work for basic use, expect no maintenance or bug fixes.

License in practice

Licensed under MIT (permissive), so you can use, modify, and distribute it freely with minimal restrictions.

Quickstart

pip install lambda-warmer-py

import lambda_warmer_py

@lambda_warmer_py.warmer
def your_lambda_function(event, context):
    pass

Your Lambda execution role must have permission to invoke itself (lambda:InvokeFunction) if using concurrency; CloudWatch permissions (cloudwatch:PutMetricData) are required only if send_metric=True.

Verify before relying

• Compatibility with current Python versions and AWS Lambda runtime environments given the last release was in 2019.
• Whether the package works with modern AWS Lambda architectures and whether concurrent warming still aligns with current AWS best practices.
• Whether the decorator properly integrates with current Lambda execution contexts.

Package facts

Evidence: lambda_warmer_py-0.6.0-py3-none-any.whl

Tags

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