# Build
This page collects build-time error codes and common troubleshooting guidance.
## Error Codes
- [BUILD-001](#build-001)
- [BUILD-002](#build-002)
## BUILD-001
Failed to find expose module.
### Reasons
Failed to find the Expose module resource.
There are two possible reasons:
1. The exposeModules file path configured in `exposes` is incorrect and points to a non-existing path.
2. When using `Next.js` or other frameworks with built-in webpack, the webpack path used by MF does not match the framework's webpack path.
### Solutions
1. Check whether the module file path in exposes is correct, paying attention to case sensitivity.
2. Check whether FEDERATION\_WEBPACK\_PATH matches the webpack path used by the framework. If not, verify dependencies are installed correctly or set process.env.FEDERATION\_WEBPACK\_PATH to the actual webpack path.
## BUILD-002
PublicPath is required in prod mode.
### Reasons
When building an Rspress producer, the project must set `publicPath`, otherwise it cannot be loaded normally by other consumers.
### Solutions
Set `publicPath` via one of the following methods:
- Set [builderConfig.output.assetPrefix](https://rsbuild.rs/config/output/asset-prefix) in `rspress.config.ts`
```ts title="rspress.config.ts"
export default {
builderConfig: {
output: {
assetPrefix: 'https://module-federation.io/',
}
}
}
```
- Set [builderConfig.tools.rspack](https://rsbuild.rs/config/tools/rspack) in `rspress.config.js`
```ts title="rspress.config.ts"
export default {
builderConfig: {
tools: {
rspack: (config)=>{
config.output.publicPath = 'https://module-federation.io/';
},
}
}
}
```
## Common Issues (No Error Code)
### CORS warn
When `exposes` is set in the project, it will be regarded as a producer. To ensure that the producer resources can be loaded normally by consumers, `@module-federation/modern-js-v3` and `@module-federation/rsbuild-plugin` will set `Access-Control-Allow-Origin` to `*` and issue a warning at the same time.
#### Solutions
- \[Modern.js]: Set [devServer.headers](https://modernjs.dev/configure/app/tools/dev-server.html#headers) value to the specified domain whitelist instead of `*`
- \[Rsbuild]: Set [server.cors.origin](https://rsbuild.dev/config/server/cors#origin) value to the specified domain whitelist instead of `*`
### Multiple assets emit different content to the same filename mf-manifest.json
#### Reason
In Rspack `1.6.0-beta.0`, we ported the manifest implementation to Rust. Upgrading Rspack without upgrading the MF-related packages will cause this error.
#### Solution
Upgrade the `@module-federation` scoped npm package to version 0.21.0 or later.
