Next.js request.url Returns Internal Proxy URL on Containerized Platforms

Problem

When deploying Next.js to Railway, Vercel, or similar containerized platforms, request.url in Edge runtime or API routes can return the internal proxy URL (e.g., http://localhost:8080) instead of the public domain (e.g., https://example.com).

This causes NextResponse.redirect(new URL(path, request.url)) to redirect users to the internal URL, which fails with ERR_CONNECTION_REFUSED.

Context / Trigger Conditions

• Symptom: Browser shows ERR_CONNECTION_REFUSED to localhost:8080 or similar
• Console errors: Failed to fetch RSC payload followed by connection refused
• Network tab: Shows 307 redirect to https://localhost:8080/...
• Environment: Next.js deployed to Railway, Vercel, Docker, or any reverse proxy setup
• Code pattern: Using new URL('/path', request.url) for redirects

Solution

Replace request.url with an environment variable for the public URL:

// Before (broken on containerized platforms):
return NextResponse.redirect(
  new URL(`/not-found?code=${shortCode}`, request.url)
);

// After (works everywhere):
const baseUrl = process.env.NEXT_PUBLIC_APP_URL || "https://example.com";
return NextResponse.redirect(
  new URL(`/not-found?code=${shortCode}`, baseUrl)
);

For reusable code, create a helper:

const getBaseUrl = () =>
  process.env.NEXT_PUBLIC_APP_URL || "https://example.com";

Verification

1. Deploy the fix to production
2. Visit a URL that triggers the redirect
3. Verify the redirect goes to the public domain, not localhost
4. Check browser console for absence of ERR_CONNECTION_REFUSED

Example

File: app/[shortCode]/route.ts

// Add helper at module level
const getBaseUrl = () =>
  process.env.NEXT_PUBLIC_APP_URL || "https://clicktowa.com";

export async function GET(request: NextRequest, { params }) {
  const { shortCode } = await params;
  const baseUrl = getBaseUrl();

  // ... lookup logic ...

  if (!link) {
    // Use baseUrl instead of request.url
    return NextResponse.redirect(
      new URL(`/not-found?code=${encodeURIComponent(shortCode)}`, baseUrl)
    );
  }

  // ... rest of handler
}

Notes

• This issue occurs because containerized platforms route traffic through internal load balancers/proxies. The request.url reflects the internal connection, not the original public request.

• Some platforms set headers like X-Forwarded-Host or X-Original-Host, but these aren't automatically used by request.url.

• The NEXT_PUBLIC_ prefix makes the variable available in both client and server code, which is appropriate for the public URL.

• Always provide a sensible fallback in case the env var isn't set.

• This also affects request.headers.get('host') in some configurations—always prefer explicit environment variables for public URLs.

Related Patterns

• Auth callback URLs should also use NEXT_PUBLIC_APP_URL
• OAuth redirect URIs need the public domain
• Sitemap and robots.txt generation should use the env var
• OpenGraph and canonical URLs should use the env var

References

• Next.js Environment Variables
• Railway Networking