In this post, we explore how to build an Express application on top of AWS Lambda functions, all within Netlify. Netlify and AWS Lambda integration allows developers to run arbitrary backend code without leaving the platform. The idea behind Lambda functions is that you pay for what you need and don't have to worry about responding to changes in load to your application. We use serverless-http to translate between Lambda's event object and Express's req and res object, simplifying routing decisions. Using Express in a Lambda function provides benefits such as using favorite Express patterns, existing middleware, and a large ecosystem of ready-to-use components. However, there are considerations for resource limits, including memory and execution time limits, and the need to handle "stateless" runtime, where instances may not be reused across requests. We also discuss connecting to databases and building Express.js apps with Netlify Functions.