Next.js should not parse server-environment variables inside the next.config.js during build

[AnsgarH1]

Goals

Next.js should not parse server environment variables during build but during runtime.

Currently environment variables inside the next.config.js get parsed during the build, which is a problem if you use next in docker for multiple environments. Usually this is dealt with by building a docker Image specifically for each environment, where the env-vars of the environment are provided and "baked in". I would rather build an environment agnostic Docker Image. This also specifically only applies to the next.config.js, every other environment variable gets parsed during runtime as expected.

Non-Goals

No response

Background

I have built a workaround, where i replace the env vars during build with placeholders and replace them again on startup of the docker image. You can find the repo with the example here: https://github.com/AnsgarH1/nextjs-demo-no-env-vars-in-config-when-standalone/tree/main

Also there was a discussion about this about three years ago, which lead to nothing: #21888

Proposal

Don't parse the server-environment variables inside the next.js config during build