This sounds like a classic production lesson in how small runtime changes can have outsized effects in serverless systems. Switching runtimes or environments can introduce unexpected cold-start latency, and because AWS Lambda functions are designed for short-lived executions with strict timeout limits, even a few extra seconds during initialization can cause requests to fail under real traffic conditions.
What I appreciate about this post is the reminder that deploys involving runtime upgrades should be treated like performance changes tested under realistic load and monitored closely.
These kinds of incidents reinforce how important observability, canary deployments, and cold-start awareness are when running production workloads on serverless infrastructure.