This backend plugin can be installed to serve static content of a Backstage app.

Add both this package and your local frontend app package as dependencies to your backend, for example

# From your Backstage root directory
yarn --cwd packages/backend add @backstage/plugin-app-backend app

By adding the app package as a dependency we ensure that it is built as part of the backend, and that it can be resolved at runtime.

Now add the plugin to your app, creating it for example like this:

import { createBackend } from '@backstage/backend-defaults';

const backend = createBackend();
backend.add(import('@backstage/plugin-app-backend'));
backend.start();

const router = await createRouter({
  logger: env.logger,
  appPackageName: 'example-app',
});

And registering it like this:

createServiceBuilder(module)
  ...
  .addRouter('', router);

Be sure to register the app router last, as it serves content for HTML5-mode navigation, i.e. falling back to serving index.html for any route that can't be found.