Keep Alive

What causes Lambda cold starts?

Cold starts occur when AWS needs to provision a new container for your function. This happens when your function hasn't been invoked recently or during traffic spikes requiring new instances.

How bad are Lambda cold starts?

Initialization can add 300ms-10s+ to response times depending on runtime, dependencies, and VPC configuration. Node.js and Python are faster; Java and .NET are slower. Cold starts are particularly problematic for user-facing applications.

How does Keep Alive solve Lambda cold starts?

Keep Alive sends periodic HTTP requests to your Lambda function URL or API Gateway endpoint, keeping the container warm. Unlike DIY solutions, Keep Alive:

• Handles monitoring and retries automatically
• Requires zero code changes to your Lambda
• Works with any runtime
• Maintains detailed logs of availability
• Allows custom ping intervals per endpoint

Setup guide

1. Create a simple API Gateway endpoint or Lambda Function URL that triggers your function
2. Add the URL to Keep Alive with appropriate ping interval (typically 5-10 minutes)
3. Monitor the status in the dashboard

Advanced strategies

• Multiple memory configs: For functions with multiple memory configurations, ping each configuration
• VPC connections: For VPC-connected functions, ensure your ping hits actual function code
• Critical paths: Consider separate ping endpoints for critical paths
• Regional functions: Regional functions need separate warm-up for each region

Does this affect my AWS costs?

Minimally. Lambda charges for compute time in 1ms increments, but Keep Alive's lightweight pings use very little compute time. For a typical function:

• Ping every 5 minutes = ~8,640 invocations per month
• ~100ms execution time = ~864,000ms (14.4 minutes) of compute
• Free tier includes 1M requests and 400,000 GB-seconds

In most cases, the improved user experience far outweighs the minimal cost increase.

AWS Lambda vs other platforms