Global variable in custom server since 13.4.13

[sgarnotel]

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
      Platform: linux
      Arch: x64
      Version: #26~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Jul 13 16:27:29 UTC 2
    Binaries:
      Node: 16.20.0
      npm: 8.19.4
      Yarn: 1.22.19
      pnpm: 8.5.0
    Relevant Packages:
      next: 13.4.20-canary.2
      eslint-config-next: 13.4.19
      react: 18.2.0
      react-dom: 18.2.0
      typescript: 5.1.6
    Next.js Config:
      output: N/A

Which area(s) of Next.js are affected? (leave empty if unsure)

No response

Link to the code that reproduces this issue or a replay of the bug

https://github.com/Airthium/next-global

To Reproduce

Using the reproduction, run yarn and yarn dev and open http://localhost:3000/ will pop the following error

Error [ReferenceError]: myvar is not defined

If you change next version to 13.4.12, it works

Describe the Bug

In a larger code, I use a global variable (here global.myvar) defined when the custom server starts, in order to start my database, and store a function. I use this function in the server-side to perform queries and stop the database when I stop the server.
It worked like a charm until next 13.4.12.

Since next 13.4.13, the global variable is not available in the server side.

Expected Behavior

Same behavior of next 13.4.12

Which browser are you using? (if relevant)

Chrome 115.0.5790.170

How are you deploying your application? (if relevant)

custom server

[balazsorban44]

Closing in favor of #54440. Feel free to comment there! (The title might sound differently, but it's essentially the same cause)

[github-actions]

This closed issue has been automatically locked because it had no new activity for 2 weeks. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.