Functions run on Node.js 24, and requests wait while one wakes up

A function with nothing to do scales to zero and starts again on its next request. When a crowd arrived while it was starting, some of those visitors could get an error page instead of an answer, and a function at its concurrency limit answered the next request with an error.

Two things changed. Functions run on Node.js 24, and a request that reaches a function while it wakes up, or while it's busy, now waits its turn at the edge.

What changed#

• Node.js 24. Functions run on Node.js 24 LTS, the default runtime. A function created with nodejs20 or nodejs22 runs on Node.js 24 as well.
• Waking on demand. A sleeping function wakes on its next request. Every request that arrives while it starts waits for that same wake, then goes through.
• A busy function. Past its Max concurrency, a request waits for a free slot instead of getting an error page.
• Visitors who leave. A request whose visitor closes the connection drops out of the line, and the wake goes on for everyone else.
• Still bounded. If the function stays busy, or more requests arrive than the edge can hold for it, a request gets an error page that tells the client to retry.
• Checks don't wake it. An uptime check of a sleeping function shows Asleep and leaves it asleep.

Get started#

1. In the dashboard, go to Gateway → Applications, open your function and its Function tab to see its runtime.
2. On the Settings tab, set Max concurrency, and Idle time (0 keeps the function awake), then click Save settings.
3. Turn on health checks for its endpoint to see Asleep or Up in the Uptime card on the Overview tab.
4. Read the docs: Serverless functions and Runtimes.