Issue with next-intl redirects when using CloudFront as a reverse proxy

[FourwingsY]

My project is hosted on Vercel at project.vercel.app, and I am using CloudFront as a CDN/WAF with a custom domain myproject.com.

The current flow and the issue:

• A user accesses myproject.com.
• CloudFront proxies the request to project.vercel.app.
• next-intl detects the locale and triggers a redirect based on the incoming request URL.
• However, it redirects to the Vercel deployment URL project.vercel.app/en instead of the custom domain myproject.com/en.
• As a result, the user is moved away from my custom domain to the Vercel internal URL.

It seems next-intl relies on request.url for redirects. Even if I set an environment variable for the base URL, I cannot find a way to force next-intl to use the custom domain for its internal redirect logic.

Is there a recommended way to handle redirects when the application is served behind a reverse proxy?

[amannn]

Can you check if your reverse proxy sets x-forwarded-host correctly?

[FourwingsY]

I am currently investigating the header settings on my reverse proxy. In the meantime, I have a follow-up question regarding the next-intl configuration:

After reviewing the internal logic, it appears that next-intl might require the domains option to be explicitly configured in defineRouting in order to respect the x-forwarded-host header for redirects. Could you confirm if this is the case?

If so, would the following configuration be the correct approach to ensure redirects stay on myproject.com?

export const routing = defineRouting({
  locales: SUPPORTED_LOCALES,
  defaultLocale: DEFAULT_LOCALE,
  domains: [{
    domain: "myproject.com",
    defaultLocale: DEFAULT_LOCALE,
    locales: SUPPORTED_LOCALES,
  }],
})

[amannn]

domains should only be necessary for domain-based routing.

It could be that there's a bug here in next-intl, but it'd be kind of odd that it's only discovered by now.

I'd like to better understand which headers are hitting your Vercel-hosted instance. I think ideally we could compare headers like x-forwarded-host, host etc. with a regular Vercel setup to diagnose if something is bad with the reverse proxy or if next-intl is missing something here. I think Next.js also does some normalization internally, so that's another aspect to consider.

Can you post your results here once you have them, ideally with a comparison to just plain Vercel?

[FourwingsY]

Well, As I know, AWS Cloudfront does not add headers by default. What I found was

• I need to add header manually on cloudfront.