plugin-full-frontend-system-migration（插件完整前端系统迁移）

Full Plugin Migration to the New Frontend System

This skill helps fully migrate an existing Backstage plugin from the old frontend system to the new one. Unlike adding dual support (which keeps the old system working), this is a complete migration that removes all @backstage/core-plugin-api usage and makes the plugin work exclusively with the new frontend system.

This is the preferred approach for internal plugins that are only used in a single app, since there is no need to maintain backward compatibility. It can also be used for published plugins when you're ready to drop old system support entirely.

It is highly recommended to be on Backstage version 1.49.x or above before starting this, although not mandatory, you may face issues with some of the instructions below. This can be verified by looking in the backstage.json file in the root of the repository.

Key Differences from Dual Support

Step 1: Migrate Route Refs

Replace createRouteRef / createSubRouteRef / createExternalRouteRef imports:

// OLD (src/routes.ts)
import {
  createRouteRef,
  createSubRouteRef,
  createExternalRouteRef,
} from '@backstage/core-plugin-api';

export const rootRouteRef = createRouteRef({ id: 'my-plugin' });
export const detailsRouteRef = createSubRouteRef({
  id: 'my-plugin-details',
  parent: rootRouteRef,
  path: '/details/:id',
});
export const externalDocsRouteRef = createExternalRouteRef({ id: 'docs' });

// NEW (src/routes.ts)
import {
  createRouteRef,
  createSubRouteRef,
  createExternalRouteRef,
} from '@backstage/frontend-plugin-api';

export const rootRouteRef = createRouteRef();
export const detailsRouteRef = createSubRouteRef({
  path: '/details/:id',
  parent: rootRouteRef,
});
export const externalDocsRouteRef = createExternalRouteRef({
  defaultTarget: 'techdocs.docRoot',
});

Key differences:

• createRouteRef() no longer takes an id — the ID is derived from the extension
• createSubRouteRef path must start with / and must not end with /
• createExternalRouteRef() no longer takes an id or optional flag

Set Default Targets for External Route Refs

When migrating external route refs, always set defaultTarget to the most common binding target. This removes the need for apps to explicitly bind routes via bindRoutes for standard plugin combinations:

export const createComponentRouteRef = createExternalRouteRef({
  defaultTarget: 'scaffolder.root',
});

export const viewTechDocRouteRef = createExternalRouteRef({
  params: ['namespace', 'kind', 'name'],
  defaultTarget: 'techdocs.docRoot',
});

export const catalogEntityRouteRef = createExternalRouteRef({
  params: ['namespace', 'kind', 'name'],
  defaultTarget: 'catalog.catalogEntity',
});

The defaultTarget string uses the <pluginId>.<routeName> format, where routeName matches a key in the target plugin's routes map. The default is only activated when the target plugin is installed — otherwise the route stays unbound and useRouteRef returns undefined.

This is especially important for a full migration because in the old system, apps typically had explicit bindRoutes calls. With default targets, most of those bindings become unnecessary, improving the plug-and-play experience.

Step 2: Migrate the Plugin Definition

Replace src/plugin.ts with a createFrontendPlugin-based definition:

// NEW (src/plugin.tsx)
import { createFrontendPlugin } from '@backstage/frontend-plugin-api';
import { RiToolsLine } from '@remixicon/react';
import { rootRouteRef, externalDocsRouteRef } from './routes';
import { myPage } from './extensions';
import { myPluginApi } from './apis';

export default createFrontendPlugin({
  pluginId: 'my-plugin',
  title: 'My Plugin',
  icon: <RiToolsLine />,
  info: {
    packageJson: () => import('../package.json'),
  },
  routes: {
    root: rootRouteRef,
  },
  externalRoutes: {
    docs: externalDocsRouteRef,
  },
  extensions: [myPluginApi, myPage],
});

For the plugin icon, prefer using Remix Icons from @remixicon/react. If the plugin already has an existing MUI icon, it can be kept with fontSize="inherit" (e.g. <CategoryIcon fontSize="inherit" />), but for new icons Remix is the recommended choice.

Since this is the only entry point now, export it as default from src/index.ts or update package.json exports accordingly. If the plugin was previously consumed via its main entry point, you can make the main entry point export the new plugin:

{
  "exports": {
    ".": "./src/index.ts",
    "./package.json": "./package.json"
  }
}

// src/index.ts
export { default } from './plugin';
export { rootRouteRef } from './routes';

Step 3: Migrate API Factories to ApiBlueprint

// OLD
import {
  createApiFactory,
  discoveryApiRef,
  fetchApiRef,
} from '@backstage/core-plugin-api';

export const myApiFactory = createApiFactory({
  api: myPluginApiRef,
  deps: { discoveryApi: discoveryApiRef, fetchApi: fetchApiRef },
  factory: ({ discoveryApi, fetchApi }) =>
    new MyPluginClient({ discoveryApi, fetchApi }),
});

// NEW (src/apis.ts)
import {
  ApiBlueprint,
  discoveryApiRef,
  fetchApiRef,
} from '@backstage/frontend-plugin-api';
import { myPluginApiRef } from './api';

export const myPluginApi = ApiBlueprint.make({
  params: defineParams =>
    defineParams({
      api: myPluginApiRef,
      deps: { discoveryApi: discoveryApiRef, fetchApi: fetchApiRef },
      factory: ({ discoveryApi, fetchApi }) =>
        new MyPluginClient({ discoveryApi, fetchApi }),
    }),
});

Also update the API ref creation to the new builder pattern with explicit pluginId:

// OLD
import { createApiRef } from '@backstage/core-plugin-api';

export const myPluginApiRef = createApiRef<MyPluginApi>({
  id: 'plugin.my-plugin.client',
});

// NEW (recommended builder pattern with explicit pluginId)
import { createApiRef } from '@backstage/frontend-plugin-api';

export const myPluginApiRef = createApiRef<MyPluginApi>().with({
  id: 'plugin.my-plugin.client',
  pluginId: 'my-plugin',
});

The builder form (createApiRef<T>().with(...)) is preferred because ownership is explicit via pluginId rather than parsed from the ID string. The id must still be globally unique across the app — the pluginId is ownership metadata, not a namespace prefix.

API Ownership and Override Rules

The new system enforces API ownership — only the owning plugin (or a module targeting it) can provide or override a given API. Ownership is determined by:

1. The explicit pluginId on the ApiRef (if set via the builder pattern)
2. Falling back to inference from the ApiRef ID string:

- plugin.<pluginId>.* → owned by that plugin - core.* → owned by the app plugin

If app adopters want to replace your plugin's default API implementation, they must use a createFrontendModule with pluginId matching your plugin — they cannot override it from a different plugin or from a generic app module. This is a stricter model than the old system where any API could be overridden from the app's apis array.

Step 4: Migrate Pages to PageBlueprint

Simple Page (No Sub-Routes)

// src/extensions.tsx
import { PageBlueprint } from '@backstage/frontend-plugin-api';
import { rootRouteRef } from './routes';

export const myPage = PageBlueprint.make({
  params: {
    path: '/my-plugin',
    routeRef: rootRouteRef,
    loader: () => import('./components/MyPage').then(m => <m.MyPage />),
  },
});

The MyPage component should not include Page, Header, or PageWithHeader from @backstage/core-components. The framework's PageLayout renders PluginHeader automatically.

The title and icon params on PageBlueprint are only needed if they should differ from the plugin's own title and icon (set in createFrontendPlugin). If omitted, the plugin-level values are used.

Page with Header for Custom Actions

If your page needs a subtitle or action buttons below the framework header, use Header from @backstage/ui:

// src/components/MyPage/MyPage.tsx
import { Header } from '@backstage/ui';
import { Content } from '@backstage/core-components';

export function MyPage() {
  return (
    <>
      <Header
        title="Subtitle or description"
        customActions={
          <>
            <CreateButton title="Create" to="/my-plugin/create" />
            <SupportButton>Help text</SupportButton>
          </>
        }
      />
      <Content>
        <MyPageContent />
      </Content>
    </>
  );
}

Page Without Header

For pages that manage their own layout entirely (e.g. home page, dashboards), set noHeader: true:

export const myPage = PageBlueprint.make({
  params: {
    path: '/my-plugin',
    routeRef: rootRouteRef,
    noHeader: true,
    loader: () => import('./components/MyPage').then(m => <m.MyPage />),
  },
});

Step 5: Replace Internal Routing with Sub-Pages

Old frontend plugins often use React Router <Route> trees inside a router component to handle internal navigation. Before migrating, determine which routing pattern fits the plugin.

Decide Which Routing Pattern to Use

Not all internal routing maps to tabs. Read the plugin's existing router component and ask the user:

"Does your plugin use top-level tabs that users navigate between via a header (e.g. Overview / Settings)? Or does it use detail/drill-down routes (e.g. /my-plugin/items/:id)?"

Use SubPageBlueprint when:

• The sub-routes represent top-level tabs/sections of the plugin
• Users navigate between them via the header

Keep internal routing within a PageBlueprint loader when:

• Routes are detail/drill-down pages (e.g. /my-plugin/items/:id)
• The routing is deeply nested or dynamic

If the plugin uses drill-down routing only, use a PageBlueprint with a loader that handles its own <Routes> and skip the rest of this step:

export const myPage = PageBlueprint.make({
  params: {
    path: '/my-plugin',
    routeRef: rootRouteRef,
    loader: () => import('./components/Router').then(m => <m.MyPluginRouter />),
  },
});

If the plugin uses top-level tabs, continue with the SubPageBlueprint migration below.

Old Pattern: Internal Router

// OLD — plugin owns its own routing
import { Route, Routes } from 'react-router-dom';

export function MyPluginRouter() {
  return (
    <Page themeId="tool">
      <Header title="My Plugin" />
      <HeaderTabs
        tabs={[
          { id: 'overview', label: 'Overview' },
          { id: 'settings', label: 'Settings' },
        ]}
      />
      <Content>
        <Routes>
          <Route path="/" element={<OverviewPage />} />
          <Route path="/settings" element={<SettingsPage />} />
        </Routes>
      </Content>
    </Page>
  );
}

New Pattern: PageBlueprint + SubPageBlueprint

// src/extensions.tsx
import {
  PageBlueprint,
  SubPageBlueprint,
} from '@backstage/frontend-plugin-api';

// Parent page WITHOUT a loader — uses built-in tabbed rendering
export const myPluginPage = PageBlueprint.make({
  params: {
    path: '/my-plugin',
    routeRef: rootRouteRef,
  },
});

export const overviewSubPage = SubPageBlueprint.make({
  name: 'overview',
  params: {
    path: 'overview',
    title: 'Overview',
    loader: () =>
      import('./components/OverviewPage').then(m => <m.OverviewPageContent />),
  },
});

export const settingsSubPage = SubPageBlueprint.make({
  name: 'settings',
  params: {
    path: 'settings',
    title: 'Settings',
    loader: () =>
      import('./components/SettingsPage').then(m => <m.SettingsPageContent />),
  },
});

How this works:

• PageBlueprint without a loader automatically renders its sub-pages as tabs
• The first sub-page becomes the default (index redirect)
• Each SubPageBlueprint gets a tab in the header with its title
• Sub-page path values are relative (no leading /)
• Sub-page components render content only — no Page, Header, or HeaderTabs

If the sub-page content needs padding, use Container from @backstage/ui as a wrapper inside the component.

Step 6: Update Hooks and Imports

Replace all @backstage/core-plugin-api imports with @backstage/frontend-plugin-api:

// OLD
import { useApi, useRouteRef, configApiRef } from '@backstage/core-plugin-api';

// NEW
import {
  useApi,
  useRouteRef,
  configApiRef,
} from '@backstage/frontend-plugin-api';

useRouteRef Behavior Change

In the new system, useRouteRef may return undefined for external route refs that aren't bound. Handle this:

// OLD — throws if not bound
const docsLink = useRouteRef(externalDocsRouteRef);
// Always a function

// NEW — returns undefined if not bound
const docsLink = useRouteRef(externalDocsRouteRef);
if (docsLink) {
  // render link
}

Common Import Mappings

Step 7: Remove Old System Code

1. Delete src/plugin.ts (old createPlugin)
2. Delete any createRoutableExtension / createComponentExtension usage
3. Remove Page, Header, PageWithHeader wrapping from page components
4. Remove HeaderTabs if replaced by SubPageBlueprint tabs
5. Remove internal <Routes>/<Route> trees if replaced by sub-pages
6. Remove @backstage/core-plugin-api from package.json dependencies
7. Remove @backstage/core-compat-api from package.json dependencies if present

Step 8: Update Page Components for BUI

With the full migration, page components should use @backstage/ui components and patterns. See the mui-to-bui-migration skill for detailed component migration guidance.

Key page-level changes:

• Replace PageWithHeader / Page + Header with framework-provided PluginHeader (automatic via PageLayout)
• Use Header from @backstage/ui for optional subtitle/custom actions
• Use Content from @backstage/core-components for page body padding (this is still used even in NFS pages)
• Replace ContentHeader with Header's customActions prop
• Replace HeaderTabs with SubPageBlueprint (tabs are rendered by the framework)

Real Example: Auth Plugin (Fully Migrated)

The @backstage/plugin-auth plugin is a fully migrated example with no @backstage/core-plugin-api dependency:

// plugins/auth/src/routes.ts
import { createRouteRef } from '@backstage/frontend-plugin-api';

export const rootRouteRef = createRouteRef();

// plugins/auth/src/plugin.tsx
import {
  createFrontendPlugin,
  PageBlueprint,
} from '@backstage/frontend-plugin-api';
import { rootRouteRef } from './routes';

export const AuthPage = PageBlueprint.make({
  params: {
    path: '/oauth2',
    routeRef: rootRouteRef,
    loader: () => import('./components/Router').then(m => <m.Router />),
  },
});

export default createFrontendPlugin({
  pluginId: 'auth',
  extensions: [AuthPage],
  routes: {
    root: rootRouteRef,
  },
});

Real Example: Scaffolder Sub-Pages

The scaffolder plugin demonstrates the sub-page pattern (though it still has dual support — the pattern itself is what a full migration targets):

// PageBlueprint WITHOUT loader — framework renders tabs
export const scaffolderPage = PageBlueprint.make({
  params: {
    path: '/create',
    routeRef: rootRouteRef,
  },
});

// Sub-pages with content only
export const templatesSubPage = SubPageBlueprint.make({
  name: 'templates',
  params: {
    path: 'templates',
    title: 'Templates',
    loader: () => import('./TemplatesPage').then(m => <m.TemplatesSubPage />),
  },
});

export const tasksSubPage = SubPageBlueprint.make({
  name: 'tasks',
  params: {
    path: 'tasks',
    title: 'Tasks',
    loader: () => import('./TasksPage').then(m => <m.TasksSubPage />),
  },
});

Migration Checklist

1. Migrate route refs to @backstage/frontend-plugin-api (createRouteRef, createSubRouteRef, createExternalRouteRef)
2. Replace createPlugin with createFrontendPlugin
3. Convert all API factories to ApiBlueprint extensions
4. Convert pages to PageBlueprint
5. Replace internal tab routing with SubPageBlueprint where appropriate
6. Remove Page/Header/PageWithHeader from page components
7. Add Header from @backstage/ui where subtitle/custom actions are needed
8. Replace HeaderTabs with SubPageBlueprint tabs
9. Update all @backstage/core-plugin-api imports to @backstage/frontend-plugin-api
10. Handle useRouteRef possibly returning undefined
11. Remove src/plugin.ts (old system entry point)
12. Remove src/alpha.tsx if it existed (merge into main entry)
13. Remove @backstage/core-plugin-api from package.json dependencies
14. Remove @backstage/core-compat-api from package.json dependencies
15. Update package.json exports (remove ./alpha if merged into main)
16. Run yarn tsc to check for type errors
17. Run yarn lint to check for missing dependencies
18. Run yarn build:api-reports to update API reports (if the project uses API reports)
19. Test in a new-system app (packages/app)

Reference

• Plugin migration guide
• Extension blueprints
• Utility APIs
• MUI to BUI migration: mui-to-bui-migration skill