Next.js Standalone + Payload CMS: All Static Assets Return 404 in Docker container

[vdevc]

I'm running Payload CMS in a Next.js monorepo,

my-project/
├── apps/
│   ├── cms/
│   │   ├── Dockerfile
│   │   ├── package.json
│   │   ├── .env
│   │   ├── src/
│   │   │   ├── app/
│   │   │   ├── collections/
│   │   │   ├── fields/
│   │   │   ├── globals/
│   │   │   ├── payload.config.ts
│   │   │   └── ...
│   │   ├── public/
│   │   ├── .next/
│   │   └── ...
│   ├── website/
│   └── helpcenter/
├── packages/
│   ├── shared-components/
│   └── shared-types/
├── node_modules/
├── package.json
├── pnpm-lock.yaml
├── pnpm-workspace.yaml
├── .dockerignore
├── docs/
└── ...

using the recommended build and deploying via Docker. The build and container start without errors, and all static assets (CSS, JS) are present in /app/.next/static inside the container.

this is the next.config.mjs

const nextConfig = {
  // Your Next.js config here
  output: 'standalone',
  // In a monorepo, trace from the workspace root so standalone includes needed files
  outputFileTracingRoot: path.join(process.cwd(), '../..'),
  [...]
}

However, when accessing the app running in container (Docker, mapped port), all requests to /_next/static/* (e.g. CSS, JS) return 404, even though the files exist and are not empty. This happens for all assets, not just CSS.

• No reverse proxy is used (i plan to use one but for now the test is local), only direct port mapping (e.g. -p 9035:3000).
• The Dockerfile copies both the standalone build and .next/static to the container root.
• The server is started with node apps/cms/server.js.
• The same setup works in local dev (next dev), with all assets loading correctly.
• No custom basePath or assetPrefix is set in next.config.mjs.

Payload CMS UI loads, but without styles/scripts when running in docker.

What could cause Next.js standalone to return 404 for all static assets in Docker, despite the files being present? Is there a known issue or required config for Payload CMS + Next.js in monorepo/standalone builds?

Any help or pointers appreciated!

[b3nab]

Ehy I remember I had a similar issue with docker and nextjs standalone output.

Take a look at the official example of dockerfile https://github.com/vercel/next.js/blob/canary/examples/with-docker/Dockerfile from nextjs repository.

I tweaked that a bit to accept some custom args I use and make it work with monorepo, anyway the lines that copy files are already in the dockerfile:

# Automatically leverage output traces to reduce image size
# https://nextjs.org/docs/advanced-features/output-file-tracing
COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static

However I saw my setup and I only have output variable set but not the outputFileTracingRoot since I edited the dockerfile to use the monorepo with two env variables:

APP_DIR=/apps/mypayloadapp # this is the folder of the app I want to build
CI_BUILD_COMMAND=ci:myapp:build # this command is from the root /package.json

And so I changed the Dockerfile a bit like the following:

# Automatically leverage output traces to reduce image size
# https://nextjs.org/docs/advanced-features/output-file-tracing
COPY --from=builder --chown=nextjs:nodejs /app${APP_DIR}/.next/standalone ./
COPY --from=builder --chown=nextjs:nodejs /app${APP_DIR}/.next/static .${APP_DIR}/.next/static