NEXT_PUBLIC Environment Variables not avaliable on Client in Standalone

[SIMULATAN]

Verify canary release

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

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #49~20.04.1-Ubuntu SMP Wed May 18 18:44:28 UTC 2022
Binaries:
  Node: 18.3.0
  npm: 8.11.0
  Yarn: N/A
  pnpm: N/A
Relevant packages:
  next: 12.1.7-canary.31
  react: 17.0.2
  react-dom: 17.0.2

What browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

Docker Image with Standalone

Describe the Bug

Environment Variables set at Runtime don't work on the client, only on the server, even when prefixed with NEXT_PUBLIC_.
This also happens with a loaded .env file

Expected Behavior

Environment Variables with the NEXT_PUBLIC_ prefix are useable in the browser

To Reproduce

1. make a docker image with the standalone version
2. run the image with a environment variable NEXT_PUBLIC_TESTVAR supplied via docker env vars
3. try to access the variable in a page with process.env.NEXT_PUBLIC_TESTVAR - it'll return undefined

[flex-jonghyen]

I have same problem on middleware

[balazsorban44]

This is expected as per the docs:

The value will be inlined into JavaScript sent to the browser because of the NEXT_PUBLIC_ prefix. This inlining occurs at build time, so your various NEXT_PUBLIC_ envs need to be set when the project is built.

See:
https://nextjs.org/docs/basic-features/environment-variables#exposing-environment-variables-to-the-browser

[github-actions]

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