Migrating Plugins

This guide allows you to migrate a frontend plugin and its own components, routes, apis to the new frontend system.

The main concept is that routes, components, apis are now extensions. You can use the appropriate extension blueprints to migrate all of them to extensions.

Migrating the plugin

In the legacy frontend system a plugin was defined in its own plugin.ts file as following:

my-plugin/src/plugin.ts

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

  export const myPlugin = createPlugin({
    id: 'my-plugin',
    apis: [],
    routes: {
      ...
    },
    externalRoutes: {
      ...
    },
  });

In order to migrate the actual definition of the plugin you need to recreate the plugin using the new createFrontendPlugin utility exported by @backstage/frontend-plugin-api. The new createFrontendPlugin function doesn't accept apis anymore as apis are now extensions.

my-plugin/src/alpha.ts

  import { createFrontendPlugin } from '@backstage/frontend-plugin-api';

  export default createFrontendPlugin({
    id: 'my-plugin',
    // bind all the extensions to the plugin
    extensions: [],
    // convert old route refs to the new system
    routes: convertLegacyRouteRefs({
      ...
    }),
    externalRoutes: convertLegacyRouteRefs({
      ...
    }),
  });

The code above binds all the extensions to the plugin. Important: Make sure to export the plugin as default export of your package as a separate entrypoint, preferably /alpha, as suggested by the code snippet above. Make sure src/alpha.ts is exported in your package.json:

my-plugin/package.json

  "exports": {
    ".": "./src/index.ts",
    "./alpha": "./src/alpha.ts",
    "./package.json": "./package.json"
  },
  "typesVersions": {
    "*": {
      "alpha": [
        "src/alpha.ts"
      ],
      "package.json": [
        "package.json"
      ]
    }
  },

Migrating Pages

Pages that were previously created using the createRoutableExtension extension function can be migrated to the new Frontend System using the PageBlueprint extension blueprint, exported by @backstage/frontend-plugin-api.

For example, given the following page:

export const FooPage = fooPlugin.provide(
  createRoutableExtension({
    name: 'FooPage',
    component: () => import('./components').then(m => m.FooPage),
    mountPoint: rootRouteRef,
  }),
);

it can be migrated as the following:

import { PageBlueprint } from '@backstage/frontend-plugin-api';
import {
  compatWrapper,
  convertLegacyRouteRef,
} from '@backstage/core-compat-api';

const fooPage = PageBlueprint.make({
  params: {
    defaultPath: '/foo',
    // you can reuse the existing routeRef
    // by wrapping into the convertLegacyRouteRef.
    routeRef: convertLegacyRouteRef(rootRouteRef),
    // these inputs usually match the props required by the component.
    loader: ({ inputs }) =>
      import('./components/').then(m =>
        // The compatWrapper utility allows you to use the existing
        // legacy frontend utilities used internally by the components.
        compatWrapper(<m.FooPage />),
      ),
  },
});

Then add the fooPage extension to the plugin:

my-plugin/src/alpha.ts

  import { createFrontendPlugin } from '@backstage/frontend-plugin-api';

  export default createFrontendPlugin({
    id: 'my-plugin',
    // bind all the extensions to the plugin
    extensions: [],
    extensions: [fooPage],
    ...
  });

Migrating Components

The equivalent utility to replace components created with createComponentExtension depends on the context within which the component is used, typically indicated by the naming pattern of the export. Many of these can be migrated to one of the existing blueprints, but in rare cases it may be necessary to use createExtension directly.

Migrating APIs

There are a few things to keep in mind in regards to utility APIs.

React package interface and ref changes

Let's begin with your -react package. The act of exporting TypeScript interfaces and API refs have not changed from the old system. You can typically keep those as-is. For illustrative purposes, this is an example of an interface and its API ref:

in @internal/plugin-example-react

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

/**
 * Performs some work.
 * @public
 */
export interface WorkApi {
  doWork(): Promise<void>;
}

/**
 * The work interface for the Example plugin.
 * @public
 */
export const workApiRef = createApiRef<WorkApi>({
  id: 'plugin.example.work',
});

Note at the top of the file that it uses the updated import from @backstage/frontend-plugin-api that we migrated in the previous section, instead of the old @backstage/core-plugin-api.

Now let's migrate the implementation of the api. Before we changed the core-plugin-api imports the api would have looked somewhat similar to the following:

in @internal/plugin-example, NOTE THIS IS LEGACY CODE

import { storageApiRef, createApiFactory } from '@backstage/core-plugin-api';
import { workApiRef } from '@internal/plugin-example-react';
import { WorkImpl } from './WorkImpl';

const exampleWorkApi = createApiFactory({
  api: workApiRef,
  deps: { storageApi: storageApiRef },
  factory: ({ storageApi }) => new WorkImpl({ storageApi }),
});

The major changes we'll make are

• Change the old @backstage/core-plugin-api imports to the new @backstage/frontend-plugin-api package as per the top section of this guide
• Wrap the existing API factory in a ApiBlueprint

The end result, after simplifying imports and cleaning up a bit, might look like this:

in @internal/plugin-example

import {
  storageApiRef,
  createApiFactory,
  ApiBlueprint,
} from '@backstage/frontend-plugin-api';
import { workApiRef } from '@internal/plugin-example-react';
import { WorkImpl } from './WorkImpl';

const exampleWorkApi = ApiBlueprint.make({
  params: {
    factory: createApiFactory({
      api: workApiRef,
      deps: { storageApi: storageApiRef },
      factory: ({ storageApi }) => new WorkImpl({ storageApi }),
    }),
  },
});

Finally, let's add the exampleWorkApi extension to the plugin:

my-plugin/src/alpha.ts

  import { createFrontendPlugin } from '@backstage/frontend-plugin-api';

  export default createFrontendPlugin({
    id: 'my-plugin',
    // bind all the extensions to the plugin
    extensions: [fooPage],
    extensions: [exampleWorkApi, fooPage],
    ...
  });

Further work

Since utility APIs are now complete extensions, you may want to take a bigger look at how they used to be used, and what the new frontend system offers. You may for example consider adding configurability or inputs to your API, if that makes sense for your current application.