# Lambda Web Functions

> A real Node.js web server on Lambda, billed on CPU used, 64 to 128 requests per environment. The future of HTTP business logic on AWS. Not in Sydney yet.

- Verdict: Watching
- Vendor: AWS
- Layer: [Compute](https://cloudlesslabs.com/stack/layers/compute.md). Job: HTTP business logic, once in your region
- Last reviewed: 18 October 2026, by Nicolas Dao (Cloudless Labs, Sydney)
- Web page: https://cloudlesslabs.com/stack/aws-lambda-web-functions/. The whole stack in one file: https://cloudlesslabs.com/stack/brief.md

**Warning:** Not available in all regions. Launch regions: us-east-1, us-east-2, us-west-2, ap-northeast-1 (Tokyo) and eu-west-1 (Ireland). Not in Sydney.

Announced 12 October 2026, and I'm already putting it in the stack because it changes how I'd write HTTP logic on AWS: one ordinary Express or Hono server instead of a swarm of tiny functions, with a shared database pool and billing that barely charges for waiting.

For typical APIs it costs about the same as classic Lambda; at a billion requests a month it's roughly 30% cheaper, and for long waits like LLM streaming it's as cheap as Workers. The reason to migrate isn't the price. It's the connection pool and the simpler app.

The big warning: it isn't in Sydney. Until it is, it's for workloads whose users and data sit in a launch region.

## Use it when

- HTTP APIs and server-rendered apps that mostly wait on Postgres: merge many small Lambdas into one Express or Hono app.
- Database connection pain: one environment shares one connection pool across up to 128 requests, instead of one connection per Lambda instance. This can remove the need for RDS Proxy.
- Streaming responses (LLM chat, server-sent events) when you want them on AWS.
- You want plain `node server.js` locally and code you can move anywhere.
- Slow requests: 2,000 req/s at 1 s each needs about 32 environments here, but 2,000 Lambda instances (over the default quota).

## Don't use it when

- Your users or data are in a region it hasn't reached (Sydney, today): every database query would cross an ocean.
- Anything event-driven: it's HTTP only (no SQS, S3, EventBridge or Cognito triggers).
- WebSockets: not supported (the Upgrade header is stripped).
- Heavy CPU per request: one heavy request slows every other request in the same environment.
- Flash sales above 10,000 req/s: that's the default per-endpoint cap.

## Pricing

$0.30 per million requests + $0.0000279955 per active vCPU-second + $0.0000037065 per GB-second of memory consumed while the environment lives (Sydney price-list rates; not launched there yet). Free tier: not stated.

## Gotchas, with fixes

- **Gotcha:** Up to 128 requests share one process. Lambda code that keeps the current user or tenant in a module-level variable becomes a data leak between users.
  **Fix:** Audit global variables before migrating. Keep per-request data in AsyncLocalStorage or pass it explicitly.
- **Gotcha:** A brand-new Web Function starts with a conservative per-environment concurrency limit and learns the right one from traffic. Your first big burst uses more environments and cold-starts more.
  **Fix:** Load-test before launch and judge by the second run. Lambda remembers what it learned, even after scaling to zero.
- **Gotcha:** No minimum or reserved environments, and AWS doesn't publish how fast new ones are added. A burst faster than the spare headroom waits on cold starts, and over the limits requests get HTTP 429, not a queue.
  **Fix:** Clients retry with backoff and jitter. For known spikes, put Workers in front.
- **Gotcha:** Default limits per region: 10,000 req/s per endpoint, 100,000 per account, 2,000 vCPUs (1,000 environments).
  **Fix:** Request increases ahead of growth, and set rateLimit on endpoints to protect Postgres.
- **Gotcha:** Node.js 24 on Arm64 only, 2 GB and 2 vCPU per environment.
  **Fix:** Keep anything bigger on classic Lambda.

## Provisioning

Pulumi aws-native only · No Terraform provider

Only @pulumi/aws-native (≥ v1.82.0): lambda.WebFunction, WebFunctionEndpoint, WebFunctionRevision, NetworkConnector. Not in @pulumi/aws yet (Terraform provider issue #50429 is open).

## Instead, consider

- [AWS Lambda](https://cloudlesslabs.com/stack/aws-lambda/index.md): Events, heavy compute, other languages, and regions it hasn't reached.
- [Cloudflare Workers](https://cloudlesslabs.com/stack/cloudflare-workers/index.md): WebSockets, spikes from zero, global users, rarely-hit webhooks, huge bodies.

## Worked examples

- [Lambda, Web Functions or Workers?](https://cloudlesslabs.com/stack/guides/compute-choice/index.md): Where should this piece of logic run?

## Where it fits

- [An API for my app](https://cloudlesslabs.com/stack/use-cases/api.md): pick 3. Once it's in your region, move HTTP logic to one Express app with a shared connection pool.

## In The Stack Weekly

- [Week 43: Lambda Web Functions](https://cloudlesslabs.com/weekly/2026-w43/index.md), watching

## Sources

- [Lambda Web Functions](https://docs.aws.amazon.com/lambda/latest/dg/web-functions.html)
- [Web Functions scaling](https://docs.aws.amazon.com/lambda/latest/dg/web-functions-scaling.html)

## Related

- [Compute](https://cloudlesslabs.com/stack/layers/compute.md): every tool in this layer, with its verdict
- [The whole stack in one file](https://cloudlesslabs.com/stack/brief.md): every use case and tool, for questions that span many
- [Map of every Markdown file on cloudlesslabs.com, with what each one answers](https://ask.cloudlesslabs.com)