https://zackproser.com/blog/how-to-run-background-jobs-on-vercel-without-a-queue

[royal jolt]

How to Run Background Jobs on Vercel without using a queue

[silk lance]

There is a race condition in this code. You have to await starting background jobs in your POST handler

The fact that it’s been working is just luck

And that you’ve probably been testing it locally instead of in a serverless environment

Once a handler returns vercel terminates anything you have running in the background

Meaning the fetch operations to kick off your jobs in startBackgroundJob may not even execute by the time the POST function returns

[royal jolt]

Thanks for sharing your thoughts!

If you look carefully, you'll notice that the startBackgroundJobs function actually initiates a separate route's API call (/jobs

I've been successfully using this pattern in prod for a while now:

https://github.com/zackproser/panthalia/blob/main/app/api/jobs/route.ts

and I'm primarily concerned with its performance on Vercel - where it's worked without a hitch since I've deployed it.

Hope that helps!

[silk lance]

I’m referring to this line specifically in your blog post

This function returns a promise but it isn’t being awaited.

There’s no guarantee that it will finish calling its internal logic before the handler returns (when running in serverless environment like vercel),

It’s just timing luck that it has been running without issues. It can be tested by artificially slowing down the internals of startBackgroundJob function by adding a “await a sleep function for 5 seconds” before the fetch calls. Just make sure to test it on vercel not locally.