Identify build-time vs run-time on server

[markoleavy]

Hello!
I've tried to search for that question here and on google with no luck.
Is there a way (an env variable?) to know if a server process is running at build time or at run time?
I'd like to use a cached cdn endpoint for my queries while building static pages, but then been able to switch the same queries to a non-cached server for on-request revalidation.

const endpoint = process.env.IS_BUILD_TIME ? 'https://my-cached-server.com' : 'https://my-fresh-data-server.com'

[SouthLink]

You can do this through the environment variable configuration file

In general only one .env.local file is needed. However, sometimes you might want to add some defaults for the development (next dev) or production (next start) environment.

Next.js allows you to set defaults in .env (all environments), .env.development (development environment), and .env.production (production environment).

.env.local always overrides the defaults set.

Default Environment Variables

[markoleavy]

Hi @SouthLink, thank you for your answer.
I know about env variables, but I'm to getting how to make it useful for my aim, as adding a new variable for production env will make it available on both build-time and runtime.

[icyJoseph]

Have you search on the discussions? IIRC, there used to be process.env.NEXT_PHASE === PHASE_PRODUCTION_BUILD but also there's a process.env that Next.js sets when building... I can try to look it up for you, but this has been answered in discussions before, though, not for App Router, I think.

[icyJoseph]

yeah, NEXT_PHASE is still there, and the PHASE_PRODUCTION_BUILD you get from next/constants, though these are not very well documented now, they used to be...

Though I'd say, you can also try to inject your own env var in next.config.js, using the config as function option.

[markoleavy]

Thanks a lot @icyJoseph, that is exactly what I was looking for!

[theoephraim]

@icyJoseph - from what I can tell this is no longer accurate. Logging process.env.NEXT_PHASE both in my next.config.mjs and in a specific page are both showing undefined.

[icyJoseph]

As said, these are not very well documented now, and although, some test/e2e files use them:

• https://github.com/search?q=repo%3Avercel%2Fnext.js%20NEXT_PHASE&type=code

it might not be the best idea, unless something else is not possible... that being said...

In next.config the value for NEXT_PHASE is not yet filled into the env object, by Next.js, you have to use the function form of the config:

/** @type {import('next').NextConfig} */
const nextConfig = (phase, { defaultConfig }) => {
  console.log("config", phase);
  return defaultConfig;
};

export default nextConfig;

See here, https://stackblitz.com/edit/nextjs-psvynq?file=next.config.mjs

And, as for a page, I can see it (stackblitz doesn't like 14.2.4 to build), locally:

yarn run v1.22.19
$ next build
config phase-production-build
config phase-production-build
  ▲ Next.js 14.2.4

   Creating an optimized production build ...
config phase-production-build
config phase-production-build
config phase-production-build
 ✓ Compiled successfully
 ✓ Linting and checking validity of types
 ✓ Collecting page data
   Generating static pages (0/6)  [    ]
page phase-production-build

page phase-production-build
 ✓ Generating static pages (6/6)
 ✓ Collecting build traces
 ✓ Finalizing page optimization