Webpack5 enabled API Route return Internal Server Error when deployed to vercel, but works fine locally

[agustinusnathaniel]

What version of Next.js are you using?

10.1.3

What version of Node.js are you using?

14.15.3

What browser are you using?

Chrome

What operating system are you using?

Windows 10

How are you deploying your application?

Vercel

Describe the Bug

I have a project which have an API route which returns collection of data from markdowns using gray-matter. Works fine locally and when deployed to vercel. But problem occurs when I enable the webpack5 configuration in next.config.js, now the api route works fine locally, but it returns ISE (Internal Server Error) when deployed to vercel.

Expected Behavior

The api route should works fine locally and when being deployed to vercel with webpack5 enabled.

To Reproduce

Sample Repository to reproduce: https://github.com/sozonome/nextjs-webpack5-api-route-vercel-deployment-error
https://github.com/sozonome/nextjs-webpack5-api-route-vercel-deployment-error/blob/main/next.config.js

Expected (local dev screenshot):

Deployed (in vercel):
https://nextjs-webpack5-api-route-vercel-deployment-error.vercel.app/api/posts

[dohomi]

@sozonome are you using i18n? I realized all my API routes on Vercel are now prepended with the locales and not available any longer as they used before. This results on all my API functions to result in 404

This seems like a major change after 10.1.3

[agustinusnathaniel]

Nope, I didn't use / configure i18n, you can check the repo I attached.

My case only happened when I enable webpack5 and the internal server error only occurs in production deployment using vercel.

[dohomi]

@sozonome maybe we both don't have the same issue, but maybe open the deployment on Vercel and see inside of function if your function call is present. I just realized that on Vercel all my calls are prefixed with [locale] which leads online to all API calls to fail.

[agustinusnathaniel]

Yes I already confirm by checking my vercel deployment, it doesn't have any i18n prefix 😁

[dohomi]

@sozonome yes I agree has nothing to do with i18n. I stripped it all down, the error only occurs in my Vercel deployements with webpack5 enabled, if I disable it and re-deploy the API routes are working again.

[ijjk]

We've landed a patch for this and it should be available soon, will update here when it is!

[ijjk]

The above mentioned patch is now available, please re-deploy your application and give it a try!