Multi-Environment Builds#

Rsbuild supports building outputs for multiple environments at the same time. You can use environments to build multiple environments in parallel and set a different Rsbuild config for each environment.

What is environment#

The environment refers to the runtime environment for build output. Common environments include browsers, Node.js, and Workers. Rsbuild allows you to define any environment names and set build options for each environment individually.

A typical scenario is server-side rendering (SSR). You can define two environments, web and node, where the build targets (output.target) are web and node. These are used for client-side rendering (CSR) and server-side rendering (SSR) scenarios.

You can also define different environments for the same build target, for example:

• Define rsc and ssr environments, both targeting node, used separately for React Server Components and SSR.
• Define desktop and mobile environments, both targeting web, used separately for desktop and mobile browsers.

Without the environments configuration, you would need to define multiple configurations for these scenarios and run multiple independent Rsbuild builds. Now, with the environments configuration, you can complete the build for multiple outputs in a single Rsbuild run (Rsbuild achieves this using Rspack's MultiCompiler).

In Rsbuild, each environment is associated with an Rsbuild configuration, an Rspack configuration, and a set of build outputs. Rsbuild plugin developers can customize the build process for a specified environment based on the environment name, such as modifying Rsbuild or Rspack configurations, registering or removing plugins, adjusting Rspack rules, and viewing assets information.

Environment configs#

Rsbuild supports defining different Rsbuild configs for each environment through environments.

For example, if your project wants to support the SSR function, you need to define different configs for client and SSR respectively. You can define a web and node environment respectively.

export default {
  environments: {
    // Configure the web environment for browsers
    web: {
      source: {
        entry: {
          index: './src/index.client.js',
        },
        alias: {
          '@common': './src/client/common',
        },
      },
      output: {
        // Use 'web' target for the browser outputs
        target: 'web',
      },
    },
    // Configure the node environment for SSR
    node: {
      source: {
        entry: {
          index: './src/index.server.js',
        },
        alias: {
          '@common': './src/server/common',
        },
      },
      output: {
        // Use 'node' target for the Node.js outputs
        target: 'node',
      },
    },
  },
};

Config Merging#

If you configure environments, Rsbuild will merge the config in environments with the outer base config. When merging, the config in environments has higher priority.

In the example above, after merging the configs, Rsbuild generates two standalone environment configs for building web and node environments.

• web environments config: Generated by merging base config with environments.web
• node environments config: Generated by merging base config with environments.node

Then, Rsbuild will use these environments configs to internally generate two Rspack configs and execute a single build using Rspack’s MultiCompiler.

Debug Config#

When you execute the command npx rsbuild inspect in the project root directory, you will find the following output:

• rsbuild.config.[name].mjs: Indicates the Rsbuild config used for a certain environment during build.
• rspack.config.[name].mjs: Indicates the Rspack config corresponding to a certain environment when building.

➜ npx rsbuild inspect

Inspect config succeed, open following files to view the content:

  - Rsbuild Config (web): /project/dist/.rsbuild/rsbuild.config.web.mjs
  - Rsbuild Config (node): /project/dist/.rsbuild/rsbuild.config.node.mjs
  - Rspack Config (web): /project/dist/.rsbuild/rspack.config.web.mjs
  - Rspack Config (node): /project/dist/.rsbuild/rspack.config.node.mjs

Default environment#

When environments is not specified, Rsbuild will by default create an environment with the same name based on the currently target type (the value of output.target).

export default {
  output: {
    target: 'web',
  },
};

The above config is equivalent to a simplification of the following config:

export default {
  environments: {
    web: {
      output: {
        target: 'web',
      },
    },
  },
};

Specify environment build#

By default, Rsbuild will build all environments in the Rsbuild configuration when you execute rsbuild dev or rsbuild build. You can build only the specified environment via --environment <name>.

# Build for all environments by default
rsbuild dev

# Build for the web environment
rsbuild dev --environment web

# Build for the web and ssr environments
rsbuild dev --environment web --environment node

# Build multiple environments can be shortened to:
rsbuild dev --environment web,node

Plugin API#

Environment API#

Rsbuild server provides a series of APIs related to the build environment. Users can operate the build artifacts in a specific environment on the server side through the Rsbuild environment API.

For example, you can quickly implement an SSR function through the Rsbuild environment API in development mode:

import express from 'express';
import { createRsbuild, loadConfig } from '@rsbuild/core';

const serverRender = (serverAPI) => async (_req, res) => {
  const indexModule = await serverAPI.environments.ssr.loadBundle('index');

  const markup = indexModule.render();

  const template = await serverAPI.environments.web.getTransformedHtml('index');

  const html = template.replace('<!--app-content-->', markup);

  res.writeHead(200, {
    'Content-Type': 'text/html',
  });
  res.end(html);
};

export async function startDevServer() {
  const { content } = await loadConfig({});

  // Init Rsbuild
  const rsbuild = await createRsbuild({
    rsbuildConfig: content,
  });

  const app = express();

  // Create Rsbuild DevServer instance
  const rsbuildServer = await rsbuild.createDevServer();

  const serverRenderMiddleware = serverRender(rsbuildServer);

  app.get('/', async (req, res, next) => {
    try {
      await serverRenderMiddleware(req, res, next);
    } catch (err) {
      logger.error('SSR render error, downgrade to CSR...\n', err);
      next();
    }
  });

  // Apply Rsbuild’s built-in middlewares
  app.use(rsbuildServer.middlewares);

  // ...
}

For detailed usage, please refer to: SSR + Express Example.

Add environment dependencies#

By default, Rsbuild builds all environments in parallel. If an environment in your project depends on other environments to be compiled first, you can add the name of the environment you need to depend on to Rspack's dependencies configuration.

For example, the node environment depends on the web environment to be compiled first. You can add the following configuration:

export default {
  environments: {
    web: {},
    node: {
      tools: {
        rspack: {
          dependencies: ['web'],
        },
      },
    },
  },
};