Root Config Service

This service allows you to read configuration values out of your app-config YAML files.

Using the service

The following example shows how you can use the default config service to be able to get a config value, and then log it to the console.

import {
  coreServices,
  createBackendPlugin,
} from '@backstage/backend-plugin-api';

createBackendPlugin({
  pluginId: 'example',
  register(env) {
    env.registerInit({
      deps: {
        log: coreServices.logger,
        config: coreServices.rootConfig,
      },
      async init({ log, config }) {
        const baseUrl = config.getString('backend.baseUrl');
        log.warn(`The backend is running at ${baseUrl}`);
      },
    });
  },
});

Configuring the service

There's additional configuration that you can optionally pass to setup the config core service.

• argv - Override the arguments that are passed to the config loader, instead of using process.argv
• remote - Configure remote configuration loading

You can configure these additional options by adding an override for the core service when calling createBackend like follows:

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

const backend = createBackend();

backend.add(
  rootConfigServiceFactory({
    argv: [
      '--config',
      '/backstage/app-config.development.yaml',
      '--config',
      '/backstage/app-config.yaml',
    ],
    remote: { reloadIntervalSeconds: 60 },
  }),
);

For more advanced customization, there are several APIs from the @backstage/config-loader package that allow you to customize the implementation of the config service. The default implementation uses the ConfigSources.default method, which has the same options as the rootConfigServiceFactory function. You can use these to create your own config service implementation:

import { ConfigSources } from '@backstage/config-loader';
import { createServiceFactory } from '@backstage/backend-plugin-api';

const backend = createBackend();

backend.add(
  createServiceFactory({
    service: coreServices.rootConfig,
    deps: {},
    async factory() {
      const source = ConfigSources.default({
        argv: [
          '--config',
          '/backstage/app-config.development.yaml',
          '--config',
          '/backstage/app-config.yaml',
        ],
        remote: { reloadIntervalSeconds: 60 },
      });
      console.log(`Loading config from ${source}`);
      return await ConfigSources.toConfig(source);
    },
  }),
);

You can also use other config source such as StaticConfigSource and combine them with other sources using ConfigSources.merge(...). You can also create your own config source by implementing the ConfigSource interface.