Creating and integrating a Backstage Frontend plugin with a Backend plugin

As of July 1, 2024, all Janus IDP blogs have been archived and will no longer be updated. Some information in these posts may be outdated and may not work as described.

Introduction

This blog will provide information on how we can create a Backstage Frontend plugin as well integrating it with an existing Backstage Backend plugin. The Backend plugin we will use in this article will be the Local System Information plugin mentioned in another blog.

We will make some modifications to the backstage backend to wire the backend plugin into the Backstage app and then move on to create a new frontend plugin. Once everything is in place and we have verified the frontend plugin integration with the backend plugin, we will then analyze the code that makes it possible.

Prerequisites

To start, please make sure that the following tasks have already been performed:

• Run Backstage Showcase locally
• Created the Local System Information backend plugin
  • We will refer to this plugin as backend plugin for the remainder of this article.

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Modifying the Backstage backend

The backend plugin exposes the /system-info endpoint that is only available using curl, and is not accessible through the Backstage app by any Frontend plugin. To expose and make use of this backend plugin in our app, we will need to wire the plugin's router into the Backstage backend router.

Exporting the backend plugin router

• Create a new file named packages/backend/src/plugins/local-system-info.ts with the following content:

  packages/backend/src/plugins/local-system-info.ts

  import { createRouter } from '@internal/plugin-local-system-info-backend';
  import { Router } from 'express';
  import { PluginEnvironment } from '../types';
  
  export default async function createPlugin(env: PluginEnvironment): Promise<Router> {
    return await createRouter({
      logger: env.logger,
    });
  }

• Wire the backend plugin router into the Backstage backend router by modifying packages/backend/src/index.ts:

  • Import the newly added file for our backend plugin into the packages/backend/src/index.ts.

  • Then add the plugin into the backend by adding the following line into the main function after the existing addPlugin calls.

    packages/backend/src/index.ts

      import ...
      ...
      import sysInfo from './plugins/local-system-info';
      ...
      ...
      async function main() {
        ...
        await addPlugin({ plugin: 'search', apiRouter, createEnv, router: search });
    
        await addPlugin({plugin: 'sys-info', apiRouter, createEnv, router: sysInfo,});
        ...
      }

Modifying the package.json to run the backend plugin

The command to start the Backstage (yarn start) starts both the app and backend as well as any other workspaces found in the plugins directory, which also includes our new backend plugin.

Ideally, one would want to publish the backend and frontend plugins and then simply install that plugin to use it. But since we are setting up both the backend and frontend plugins in our local development environment, the yarn start command will try to start the app and the backend plugin along with the Backstage backend. Both the backend plugin as well as Backstage backend processes listen on port 7007. This will cause a port conflict when the Backstage app starts.

To resolve this issue, we can either modify the package.json in the root directory to add a new script to only run the app and backend, or run two commands to start the app and backend separately.

Modifying the package.json

Modify the package.json in the root directory by adding the following content in the scripts section (just after the start script entry):

package.json

{
  "name": "root",
  ...
  "scripts": {
    ...
    "start": "turbo run start --parallel",
    "start-dev": "turbo run start --filter=app --filter=backend",
    ...
  },
  ...
}

Alternate method to start Backstage

• In case one does not want to modify the package.json, an alternative method to start backstage is to run the following two commands in the root directory of the backstage-showcase repository, in two separate terminals:

yarn workspace app start
yarn workspace backend start

Modifying the backend plugin response

In the plugins/local-system-info-backend/src/service/router.ts file, move all the elements except cpus to the data element so that it is easier to parse and display in the frontend plugin:

plugins/local-system-info-backend/src/service/router.ts

const systemInfo = {
  data: {
    hostname: os.hostname(),
    operatingSystem: os.type(),
    platform: os.platform(),
    release: os.release(),
    uptime: os.uptime(),
    loadavg: os.loadavg(),
    totalMem: os.totalmem(),
    freeMem: os.freemem(),
  },
  cpus: os.cpus(),
};

Verifying that the backend plugin is available through the Backstage app

To verify the changes done to the backend plugin, run the Backstage backend with yarn start-backend in the root directory of the backstage-showcase repository.

Since we have yet to create a frontend plugin, we will still need to use a curl command to invoke the backend plugin. However, we will access the endpoint provided by the backstage backend router similar to how it would be accessed by a frontend plugin:

curl localhost:7007/api/sys-info/system-info | jq

• When running in the Backstage backend, it is accessed with a prefix of /api (from the cli or app)
• The backend plugin is exposed on the /sys-info main route (which matches the plugin name when we registered the plugin in the packages/backend/src/index.ts file)
• The API endpoint for providing system information is /system-info

After verifying the endpoint, you can now stop the backend by killing the yarn process.

---

Creating the Frontend plugin

To create a new frontend plugin, please execute the following command in the root directory of the backstage-showcase repository in a terminal:

yarn new --select plugin

When prompted to enter the ID of the plugin, please provide system-info. Here's the output from running this command in my terminal:

Verifying the new Frontend plugin

The above command will create a new Backstage frontend plugin and will also add it to the Backstage app. To verify the new plugin, run the app with yarn start-dev in the root directory of the backstage-showcase repository, or by following these steps. Once the app starts up, the new plugin can be verified by navigating to http://localhost:3000/system-info

Integrating the frontend plugin with backend plugin

The newly generated frontend plugin contains some static data that is displayed when navigating to http://localhost:3000/system-info. In this section, we will modify the frontend plugin to invoke the backend plugin API and display the data returned by that API.

Please follow the steps given below to achieve this integration:

• Delete the following directories:

  plugins/system-info/src/components/ExampleComponent
  plugins/system-info/src/components/ExampleFetchComponent

• Create a new directory named plugins/system-info/src/components/SystemInfoPage

• Create a new file named plugins/system-info/src/components/SystemInfoPage/types.ts with the following content:

  plugins/system-info/src/components/SystemInfoPage/types.ts

  import { TableColumn } from '@backstage/core-components';
  
  export const sysInfoCpuColumns: TableColumn[] = [
    {
      title: 'CPU Model',
      field: 'model',
    },
    {
      title: 'CPU Speed',
      field: 'speed',
    },
    {
      title: 'Times Idle',
      field: 'times.user',
    },
    {
      title: 'Times IRQ',
      field: 'times.irq',
    },
    {
      title: 'Times Nice',
      field: 'times.nice',
    },
    {
      title: 'Times Sys',
      field: 'times.sys',
    },
    {
      title: 'Times User',
      field: 'times.user',
    },
  ];
  
  export const sysInfoMainDataColumns: TableColumn[] = [
    { title: 'Hostname', field: 'hostname', highlight: true },
    { title: 'OS', field: 'operatingSystem', width: '10%' },
    { title: 'Platform', field: 'platform', width: '10%' },
    { title: 'CPU Model', field: 'cpuModel', width: '10%' },
    { title: 'CPU Speed', field: 'cpuSpeed', width: '10%' },
    { title: 'Total Memory', field: 'totalMem', width: '20%' },
    { title: 'Free Memory', field: 'freeMem', width: '10%' },
    { title: 'Release', field: 'release', width: '10%' },
    { title: 'Uptime', field: 'uptime', width: '10%' },
  ];
  
  type CpuData = {
    model: string;
    speed: number;
    times: CpuTimeData;
  };
  
  type CpuTimeData = {
    idle: number;
    irq: number;
    nice: number;
    sys: number;
    user: number;
  };
  
  type SysInfoMainData = {
    cpuModel: string;
    cpuSpeed: number;
    freeMem: number;
    hostname: string;
    loadavg: Array<number>;
    operatingSystem: string;
    platform: string;
    release: string;
    totalMem: number;
    uptime: number;
  };
  
  export type SysInfoData = {
    cpus: Array<CpuData>;
    data: SysInfoMainData;
    mainDataAsArray: SysInfoMainData[];
  };

• Create a new file named plugins/system-info/src/components/SystemInfoPage/SystemInfoPage.tsx with the following content:

  plugins/system-info/src/components/SystemInfoPage/SystemInfoPage.tsx

  import React from 'react';
  import useAsync from 'react-use/lib/useAsync';
  
  import { Table } from '@backstage/core-components';
  
  import { Box, Grid, Typography } from '@material-ui/core';
  
  import { configApiRef, useApi } from '@backstage/core-plugin-api';
  
  import { SysInfoData, sysInfoCpuColumns, sysInfoMainDataColumns } from './types';
  
  export const SystemInfoPage = () => {
    const config = useApi(configApiRef);
    const SYS_INFO_BACKEND_URL = 'backend.baseUrl';
  
    const { loading: isSysInfoLoading, value: sysInfoData } =
      useAsync(async (): Promise<SysInfoData> => {
        const backendUrl = config.getString(SYS_INFO_BACKEND_URL);
        const backendApiEndPoint = `${backendUrl}/api/sys-info/system-info`;
        const systemInfoData = await fetch(backendApiEndPoint)
          .then((res) => (res.ok ? res : Promise.reject(res)))
          .then((res) => res.json());
  
        // To display the main data in a table, prepare the array to contain the ONLY data we have
        systemInfoData.mainDataAsArray = [];
        systemInfoData.mainDataAsArray[0] = systemInfoData.data;
        systemInfoData.mainDataAsArray[0].cpuModel = systemInfoData.cpus[0].model;
        systemInfoData.mainDataAsArray[0].cpuSpeed = systemInfoData.cpus[0].speed;
  
        return systemInfoData;
      }, []);
  
    return (
      <>
        <Grid style={{ marginTop: '1rem' }} container spacing={2}>
          <Grid item xs={10}>
            <Table
              title="System Info Details"
              columns={sysInfoMainDataColumns}
              isLoading={isSysInfoLoading}
              data={sysInfoData?.mainDataAsArray || []}
              options={{
                padding: 'dense',
                pageSize: 1,
                emptyRowsWhenPaging: false,
                search: false,
              }}
              emptyContent={
                <Box style={{ textAlign: 'center', padding: '15px' }}>
                  <Typography variant="body1">Backend data NOT found</Typography>
                </Box>
              }
            />
          </Grid>
  
          <Grid item xs={10}>
            <Table
              title="System Info Details - CPUs"
              columns={sysInfoCpuColumns}
              isLoading={isSysInfoLoading}
              data={sysInfoData?.cpus || []}
              options={{
                padding: 'dense',
                pageSize: 10,
                emptyRowsWhenPaging: false,
                search: false,
              }}
              emptyContent={
                <Box style={{ textAlign: 'center', padding: '15px' }}>
                  <Typography variant="body1">Backend data NOT found</Typography>
                </Box>
              }
            />
          </Grid>
        </Grid>
      </>
    );
  };

• Create a new file named plugins/system-info/src/components/SystemInfoPage/index.ts with the following contents:

  plugins/system-info/src/components/SystemInfoPage/index.ts

  export { SystemInfoPage } from './SystemInfoPage';

• Modify plugins/system-info/src/plugin.ts by replacing the occurrences of ExampleComponent with SystemInfoPage (modified line is highlighted in the code block given below):

  plugins/system-info/src/plugin.ts

  import { createPlugin, createRoutableExtension } from '@backstage/core-plugin-api';
  
  import { rootRouteRef } from './routes';
  
  export const systemInfoPlugin = createPlugin({
    id: 'system-info',
    routes: {
      root: rootRouteRef,
    },
  });
  
  export const SystemInfoPage = systemInfoPlugin.provide(
    createRoutableExtension({
      name: 'SystemInfoPage',
      component: () => import('./components/SystemInfoPage').then((m) => m.SystemInfoPage),
      mountPoint: rootRouteRef,
    }),
  );
  • Before the change: import('./components/ExampleComponent').then(m => m.ExampleComponent),
  • After the change: import('./components/SystemInfoPage').then(m => m.SystemInfoPage),

Verifying the integration between the frontend plugin and backend plugin

Now that the plugin is all set, start the app if it is not already started. In case you see any errors, please restart the app with yarn start-dev in the root directory of the backstage-showcase repository, or by following these steps. Once the app starts up, navigate to http://localhost:3000/system-info. This page should provide the System Info Details as shown below:

---

Analyzing the code

With the frontend plugin integrated with the backend plugin and able to fetch the System information data from the backend and display it in the UI, let us go over the code that made it all possible.

The following files were created (or modified) to achieve this task:

• plugins/system-info/src/components/SystemInfoPage/types.ts: This file contains the following types that either handle the JSON response coming from the backend plugin or are used as table columns when displaying data:
  • CpuTimeData: Type to contain times attribute of CPU data from the backend plugin JSON response
  • CpuData: Type to contain CPU data from the backend plugin JSON response
  • SysInfoMainData: Type to contain data element from the backend plugin JSON response
  • SysInfoData: Type to contain SysInfoMainData and list (Array) of CpuData data
  • sysInfoCpuColumns: This is a list of fields that are of type TableColumn and are used to display the header for CPU columns.
  • sysInfoMainDataColumns: This is a list of fields that are of type TableColumn and are used to display the header for main data columns.
    • The field property for each element in the list maps to the field that is used to display data from the object containing data for the table.
• plugins/system-info/src/components/SystemInfoPage/SystemInfoPage.tsx: Main file to invoke the backend API and parse/display data on the UI with the main lines highlighted in the code block:
  • Gets the backend baseUrl (backend.baseUrl) from the config. This property is automatically configured and is available to the frontend plugin with the use of configApiRef
    plugins/system-info/src/components/SystemInfoPage/SystemInfoPage.tsx

        const config = useApi(configApiRef);
        ...
        const backendUrl = config.getString(SYS_INFO_BACKEND_URL);
  • Invokes the backend plugin API (${backendUrl}/api/sys-info/system-info) and extracts the JSON from the response as SysInfoData
    plugins/system-info/src/components/SystemInfoPage/SystemInfoPage.tsx

    const backendUrl = config.getString(SYS_INFO_BACKEND_URL);
    const backendApiEndPoint = `${backendUrl}/api/sys-info/system-info`;
    const systemInfoData = await fetch(backendApiEndPoint)
      .then((res) => (res.ok ? res : Promise.reject(res)))
      .then((res) => res.json());
  • To display the system information data, we are using the following two table components:
    • The first table uses sysInfoMainDataColumns for the columns and sysInfoData?.mainDataAsArray for the main data (mainDataAsArray is set after fetching the data from the backend API).
      plugins/system-info/src/components/SystemInfoPage/SystemInfoPage.tsx

          systemInfoData.mainDataAsArray = [];
          systemInfoData.mainDataAsArray[0] = systemInfoData.data;
          systemInfoData.mainDataAsArray[0].cpuModel = systemInfoData.cpus[0].model;
          systemInfoData.mainDataAsArray[0].cpuSpeed = systemInfoData.cpus[0].speed;
          ...
          <Table
            title="System Info Details"
            columns={sysInfoMainDataColumns}
            isLoading={isSysInfoLoading}
            data={sysInfoData?.mainDataAsArray || []}
          >
    • The second table uses sysInfoCpuColumns for the columns and sysInfoData?.cpus for the CPU data.
      plugins/system-info/src/components/SystemInfoPage/SystemInfoPage.tsx

          <Table
            title="System Info Details - CPUs"
            columns={sysInfoCpuColumns}
            isLoading={isSysInfoLoading}
            data={sysInfoData?.cpus || []}
          >
  • Exports the SystemInfoPage component, which contains the Grid containing the two table components defined above:
    plugins/system-info/src/components/SystemInfoPage/SystemInfoPage.tsx

        export const SystemInfoPage = () => {
          ...
        }
• plugins/system-info/src/components/SystemInfoPage/index.ts: exports the SystemInfoPage component.
• plugins/system-info/src/components/SystemInfoPage/plugin.ts: sets the component used by systemInfoPlugin to the SystemInfoPage component
  plugins/system-info/src/components/SystemInfoPage/plugin.ts

  export const SystemInfoPage = systemInfoPlugin.provide(
    createRoutableExtension({
      name: 'SystemInfoPage',
      component: () => import('./components/SystemInfoPage').then((m) => m.SystemInfoPage),
      mountPoint: rootRouteRef,
    }),
  );
  • This SystemInfoPage is used when we hit the route /system-info (set in packages/app/src/App.tsx)

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Conclusion

We have now created a new Backstage frontend plugin and integrated it with the backend plugin to display the data coming from the backend plugin. We used types to manage the JSON response and display the Table columns. This just scratches the surface of what can be done in a frontend plugin. As the backend plugin is exposing data through REST API, you can return pretty much whatever you need to process and display the result in your frontend plugin.

Hope you enjoyed this blog!!!

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Links

• Run Backstage Showcase locally
• Creating your first Backstage Backend plugin
• Creating a Frontend Plugin