AWS Lambda Web Functions bill memory 5 to 7 minutes after idle

A small web app on AWS Lambda can be billed for memory most of the hour it does nothing. Easel founder Sean Whiteman tested the feature. He found the idle period is long and cannot be shortened.

Whiteman ran six Lambda Web Functions in US East on 11 November 2026. Each kept running after its last request for between 313 and 411 seconds, which is 5 to 7 minutes. Memory charges kept accruing the whole time. Easel then compared the total cost against a run with no idle time. It writes that memory was about 88 percent of the compute and request cost at AWS list prices.

What AWS Web Functions do

AWS launched Lambda Web Functions as a new way to run a web app on Lambda. One function serves many HTTP requests from the same running copy. This is different from the normal model. In the normal model, each request may wake up a new copy. The AWS documentation page for Web Functions is the source for how the product is billed.

The idea of the product is that a web app stays warm between requests. There is no cold start on request two. The side effect is that memory stays billed while the app sits waiting. Easel measured the window and recorded 313 to 411 seconds across six runs.

Why the idle window matters

A request takes 200 milliseconds to answer. Memory then keeps running for 345 seconds. That is about 1,700 times the request time, all billed. For an app that gets a request every few minutes, memory is the main line on the invoice.

Whiteman writes that he tried to shut each environment down after 10 seconds of quiet. He then stopped. "It wasn't something we wanted to rely on in production," he writes. A shutdown this sharp can drop the next request.

The team's reading of the AWS documentation is that there is no setting to shorten the idle window. Whiteman writes: "There was no configurable idle timeout to shorten them." That is the whole reason Easel wrote the post: it picked its own compute for its product rather than Lambda Web Functions.

A team planning to move a web app to this product must count the idle memory in the budget. Do it before the move. The Hacker News thread had 60 points at the time of writing.

Source

Why we chose our own compute over AWS Lambda Web Functions, Sean Whiteman, Easel