Consider passing in the NEXT_PUBLIC_SERVER_URL at build time to the Dockerfile templates.

[karlapsite]

I was reviewing changes to the templates to pull in changes into my project, and figured I'd share some of my learnings here as I've been using this Dockerfile template for a while now.

next.config.js is baked at build time :(

Any environment variables used in next.config.js need to be provided at build time, regardless of whether --experimental-build-mode compile is used or not.

This means that any suggested builder, such as a github action, will need to be aware of the NEXT_PUBLIC_SERVER_URL and be able to pass it in:

      # Make sure to pass NEXT_PUBLIC_SERVER_URL
      - name: Build and Push to container registry
        uses: docker/build-push-action@v5
        with:
          push: ${{ github.event_name != 'pull_request' }}
          tags: ${{ env.IMAGE_TAG }}
          build-args: |
            NEXT_PUBLIC_SERVER_URL=${{ vars.NEXT_PUBLIC_SERVER_URL }}

Along with a change to the Dockerfile in the build stage

--- a/Dockerfile
+++ b/Dockerfile
@@ -20,6 +20,8 @@ RUN \

 # Rebuild the source code only when needed
 FROM base AS builder
+ARG NEXT_PUBLIC_SERVER_URL

I'd recommend adding this line to the website template for sure as the website template's next.config.js references NEXT_PUBLIC_SERVER_URL here

This may also affects VERCEL_PROJECT_PRODUCTION_URL... I'm unfamiliar with Vercel, and whether they own the build process or not.