[Bug]: Failed to run the build with "pnpm build:start" - works fine in dev mode

[abhidatta0]

System Info

System:
OS: macOS 26.0
CPU: (8) arm64 Apple M2
Memory: 189.27 MB / 16.00 GB
Shell: 5.9 - /bin/zsh
Binaries:
Node: 24.11.0 - /Users/abhirup/.nvm/versions/node/v24.11.0/bin/node
npm: 11.6.1 - /Users/abhirup/.nvm/versions/node/v24.11.0/bin/npm
pnpm: 10.24.0 - /Users/abhirup/.nvm/versions/node/v24.11.0/bin/pnpm
bun: 1.3.1 - /Users/abhirup/.bun/bin/bun
Watchman: 2025.09.15.00 - /opt/homebrew/bin/watchman
Browsers:
Chrome: 147.0.7727.102
Firefox: 149.0.2
Safari: 26.0
npmPackages:
@rspack/cli: ~1.2.0 => 1.2.8
@rspack/core: ~1.2.0 => 1.2.8
@rspack/plugin-react-refresh: ~1.0.1 => 1.0.3

Details

rspack-issue.mp4

As demonstrated in the video: pnpm start (the dev mode ) works but when trying to run the prod build it fails.

rspack.config.ts

import * as path from "node:path";
import { defineConfig } from "@rspack/cli";
import { rspack } from "@rspack/core";
import * as RefreshPlugin from "@rspack/plugin-react-refresh";
import { ModuleFederationPlugin } from "@module-federation/enhanced/rspack";

import { mfConfig } from "./module-federation.config";

const isDev = process.env.NODE_ENV === "development";

// Target browsers, see: https://github.com/browserslist/browserslist
const targets = ["chrome >= 87", "edge >= 88", "firefox >= 78", "safari >= 14"];

export default defineConfig({
context: __dirname,
entry: {
main: "./src/index.ts",
},
resolve: {
extensions: ["...", ".ts", ".tsx", ".jsx"],
},

devServer: {
port: 8081,
historyApiFallback: true,
watchFiles: [path.resolve(__dirname, "src")],
},
output: {
// You need to set a unique value that is not equal to other applications
uniqueName: "remote",
// publicPath must be configured if using manifest
publicPath: "http://localhost:8081/",
},

experiments: {
css: true,
},

module: {
rules: [
{
test: /.svg$/,
type: "asset",
},
{
test: /.css$/,
use: ["postcss-loader"],
type: "css",
},
{
test: /.(jsx?|tsx?)$/,
use: [
{
loader: "builtin:swc-loader",
options: {
jsc: {
parser: {
syntax: "typescript",
tsx: true,
},
transform: {
react: {
runtime: "automatic",
development: isDev,
refresh: isDev,
},
},
},
env: { targets },
},
},
],
},
],
},
plugins: [
new rspack.HtmlRspackPlugin({
template: "./index.html",
}),
new ModuleFederationPlugin(mfConfig),
isDev ? new RefreshPlugin() : null,
].filter(Boolean),
optimization: {
minimizer: [
new rspack.SwcJsMinimizerRspackPlugin(),
new rspack.LightningCssMinimizerRspackPlugin({
minimizerOptions: { targets },
}),
],
},
});

Reproduce link

No response

Reproduce Steps

1. Run pnpm start - it will work fine
2. Run "pnpm build && pnpm build:start" - it will fail

[Sylar-W]

I took a look at the video, and this seems to be caused by the local script rather than a production build failure in Rspack.

The failing script appears to be:

"build:start": "cd dist && rspack serve"

rspack serve starts a development compilation. After cd dist, there is no rspack.config.* in the current directory, so Rspack falls back to the default entry ./src. That means it tries to resolve ./src from dist, which matches the error in the video:

Module not found: Can't resolve './src' in '.../remote/dist'

To preview the production build output, rspack preview should be used instead of rspack serve, for example:

"build:start": "rspack preview dist"

or:

pnpm build && rspack preview

That said, I think the CLI diagnostic could be improved here. When rspack serve runs without a config and the default ./src entry does not exist, it could hint that rspack preview [dir] is the right command for serving build output.

Opened #13834 to improve this CLI hint.

[abhidatta0]

@Sylar-W thanks for resolving this.
Just to clarify, the command for pnpm build:start is wrong when generated from npx create-mf-app (I have not made any modifications).

Also, another bug :
my dev server port is 8081.

devServer: {
port: 8081,
historyApiFallback: true,
watchFiles: [path.resolve(__dirname, "src")],
}

still when i run the rspack preview command it opens in port 8080 and naturally fails to load...could it made to use the devServer port and if not found fallback to 8080.

Let me know if I will close this ticket and open a new one.

[Sylar-W]

Thanks for clarifying. You're right that the build:start script can come from the generated create-mf-app template, so that part is not a local modification.

For the preview port behavior, I agree this is a separate Rspack CLI issue. rspack preview reuses some devServer options, but it was not reusing devServer.port; unless --port was passed, it fell back to 8080.

I opened #13838 to make the preview port precedence --port > devServer.port > 8080. In the meantime, the workaround is rspack preview --port 8081.

No need to close this ticket right now; the linked PR should cover that follow-up behavior, and maintainers can decide whether they want to split or track it separately.