Next.js routes always responding with Connection: close header

[DamianEdwards]

Summary

I'm attempting to build an implementation of the TechEmpower Fortunes benchmark using Next.js 13.x and the App Router, but am running into an issue where the page route is always responding with a Connection: close header, drastically increasing the request latency as a new connection is required for each request. The app code is available here.

I've tried running in standalone mode, setting the KEEP_ALIVE_TIMEOUT environment variable, using a custom server, running in Docker, etc. but nothing seems to change the result.

I can reproduce this in a brand new Next.js app using npx create-next-app@latest on multiple machines.

Additional information

Operating System:
      Platform: win32
      Arch: x64
      Version: Windows 10 Pro
    Binaries:
      Node: 18.12.1
      npm: N/A
      Yarn: N/A
      pnpm: N/A
    Relevant packages:
      next: 13.4.7-canary.1
      eslint-config-next: 13.4.0
      react: 18.2.0
      react-dom: 18.2.0
      typescript: 5.1.3

Example

aspnet/Benchmarks#1866