Add Lambda warmer function to reduce cold starts

[aynaash]

Summary

Add an optional warmer Lambda that periodically invokes the server Lambda to keep it warm, reducing cold start frequency.

Design

• Warmer Lambda — Scheduled via EventBridge (every 5 minutes)
• Sends a special "ping" event to the server Lambda
• Server Lambda detects ping and returns immediately without processing
• Configurable concurrency (warm N instances)

Configuration

serverless:
  warmer:
    enabled: true
    interval: 5        # minutes
    concurrency: 3     # keep 3 instances warm

Infrastructure to Auto-Provision

• Warmer Lambda function
• EventBridge scheduled rule
• IAM permissions for warmer to invoke server Lambda

Server Lambda Changes

Add ping detection at the top of the handler:

if (event.__NEXTDEPLOY_WARMER) {
  return { statusCode: 200, body: "warm" };
}

Difficulty: Medium · Language: Go + JavaScript