After migrating 15 Lambdas to BunOnLambda, we saw a whopping 40% reduction in Lambda costs but also encountered 7 broken Node.js APIs. Was it worth the switch? We'll dive into the lessons learned and the gotchas that surprised us.

Introduction to BunOnLambda

BunOnLambda is a new runtime for AWS Lambda that uses the Bun JavaScript runtime under the hood. It's 3x faster than Node.js 22 and offers a significant reduction in Lambda costs. Here's an example of how to create a BunOnLambda function:

import { serve } from ' bun ' ;

serve ({ port : 3000 , fetch : ( request ) => { return new Response ( ' Hello, World! ' ); } });

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Don't even think about using BunOnLambda without understanding its quirks - we wish we'd known about the differences in error handling before deploying to production.

Migrating Node.js APIs to BunOnLambda

Migrating existing Node.js APIs to BunOnLambda can be a challenge.…