AWS Lambda Can Now Answer HTTP Directly With Web Functions

What AWS Launched

On October 12, AWS announced Lambda Web Functions, which it describes as a new serverless compute primitive where your code handles HTTP requests directly. Instead of writing a handler that receives an event, you run a server that listens on a port and answers requests the way it would on any machine. AWS names Express and Hono as frameworks that work without adapters.

Existing Lambda functions are being renamed Lambda Event Functions. AWS says this is a naming change only, with no code changes or redeployments needed.

Concurrency Is the Real Difference

A classic Lambda execution environment handles one request at a time. With Web Functions, a single warm environment can serve multiple concurrent requests, and AWS says this reduces cold starts by orders of magnitude, since a burst of traffic no longer needs a fresh environment for every request in flight.

That has a cost for code written for the old model. Anything kept in module scope, such as a cached user object or a request ID in a global, was safe when one environment only ever saw one request at a time. When several requests share an environment, that state is shared too. Code moving across should keep per-request data inside the request, the same discipline any Node.js web server already needs.

What Else It Supports

Responses can stream to the client as they are produced, using native HTTP streaming. Functions can connect into a VPC to reach private resources, and multi-Region routing can serve each request from the nearest Region.

Where It Runs Today

Node.js is the only runtime for now. The launch Regions are US East (N. Virginia), US East (Ohio), US West (Oregon), Asia Pacific (Tokyo) and Europe (Ireland), so a team whose workload has to stay in Frankfurt or Stockholm will have to wait.

The announcement does not list timeouts, memory ceilings or payload limits. Those live in the developer guide, and they are worth reading before planning a migration.

Who Should Look at It

An application that already runs as a Node.js HTTP server is the shape this was built for. A Next.js standalone build also starts its own HTTP server, which makes it a natural candidate to test, although AWS's announcement only names Express and Hono. Teams that wrapped such an app in an adapter to fit the event model may be able to drop that layer.

For new projects it is worth comparing against containers on ECS with Fargate, which already serve concurrent requests and run in Frankfurt and Stockholm today. Most teams running EKS would have been fine on ECS walks through how we weigh the container options. Choosing between them for a specific workload is part of our AWS cloud management work.

Sources: AWS What's New, Lambda Web Functions