Prerendering does not work when building Docker container

[NormySan]

Which project does this relate to?

Start

Describe the bug

When trying to build a TanStack Start project in SPA mode with Docker Vite fails to connect to the server. The build works fine outside of Docker.

3.276 [nitro] ✔ You can preview this build using bun run .output/server/index.mjs
3.277 [prerender] Prerendering pages...
3.305
3.305  ╭───────────────── [Build Info] ────────────────────╮
3.305  │                                                   │
3.305  │  - Build Directory: .output                       │
3.305  │  - Date: 1/2/2026, 5:55:52 AM                     │
3.305  │  - Nitro Version: 3.0.1-20251230-165713-6e801e22  │
3.305  │  - Nitro Preset: bun                              │
3.305  │                                                   │
3.305  ╰───────────────────────────────────────────────────╯
3.305
3.305 ℹ Spawning preview server...
3.305 ℹ bun run ./server/index.mjs
3.305
3.324 ➜ Listening on: http://localhost:46317/ (all interfaces)
3.841 [prerender] Concurrency: 10
3.842 [prerender] Crawling: /
3.855 [prerender] Prerendered 0 pages:
3.859 error: Unable to connect. Is the computer able to access the url?
3.859   path: "http://localhost:3000/",
3.859  errno: 0,
3.859   code: "ConnectionRefused"

I've also tried forcing the Nitro port to run at 3000 which ends up with the Vite prerender server failing to start instead.

Your Example Website or App

https://github.com/NormySan/tanstack-start-spa-nitro

Steps to Reproduce the Bug or Issue

1. Download repository
2. Build the docker image with docker build -t tanstack-start/nitro .

Expected behavior

I expect it to be able to connect to the server and to the pre-rendering.

Screenshots or Videos

No response

Platform

• Router / Start Version: Router 1.132.0 and Start 1.132.0
• Nitro: Nightly at latest
• Runtime: Bun
• OS: Mac OS
• Bundler: Vite
• Bundler Version: 7.1.7

Additional context

Similar to the following issue:
#5967 (comment)

[schiller-manuel]

does this work if not using nitro (just comment the plugin out) ? or does prerendering not work in general in docker?

[NormySan]

I just tried commenting out the Nitro Vite plugin and build again and that doesn't work either. I'm guessing that nitro is needed for the pre-rendering since it doesn't even start a server for the pre-renderer to visit when Nitro is not being used.

1.927 rendering chunks...
1.931 dist/server/assets/start-HYkvq4Ni.js                        0.06 kB
1.931 dist/server/assets/start.api-request-DhPN1_Dc.js            1.18 kB
1.931 dist/server/assets/demo.punk-songs-DMWh_nLf.js              1.20 kB
1.931 dist/server/assets/_tanstack-start-manifest_v-DVDDF2Vd.js   1.57 kB
1.931 dist/server/assets/start.server-funcs-DBayRK6n.js           1.60 kB
1.931 dist/server/assets/start.ssr.full-ssr-CNpWBhNP.js           1.62 kB
1.931 dist/server/assets/start.ssr.data-only-DK82-T8R.js          1.62 kB
1.931 dist/server/assets/start.ssr.spa-mode-B2Qcd2xk.js           1.73 kB
1.931 dist/server/assets/start.ssr.index-BmCCCK3g.js              1.96 kB
1.931 dist/server/assets/start.server-funcs-CnhSDiOa.js           2.74 kB
1.931 dist/server/assets/index-Bn-KsgDK.js                        4.73 kB
1.931 dist/server/assets/router-D0WcTyyP.js                      13.26 kB
1.931 dist/server/server.js                                      41.01 kB
1.931 ✓ built in 125ms
1.931 [prerender] Prerendering pages...
1.964 [prerender] Concurrency: 10
1.964 [prerender] Crawling: /
1.968 [prerender] Prerendered 0 pages:
1.968 error: Unable to connect. Is the computer able to access the url?
1.968   path: "http://localhost:45913/",
1.968  errno: 0,
1.968   code: "ConnectionRefused"
1.968
1.968
1.968 Bun v1.3.5 (Linux arm64)
1.980 error: script "build" exited with code 1

[schiller-manuel]

nitro is not needed for prerendering. so most likely the vite preview server that is used for prerendering is not accessible in the docker env

cc @edmundhung