Merge pull request #4458 from backstage/rugvip/appconfigdisable

app-backend: added disableConfigInjection option + docs

.changeset/empty-cooks-laugh.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-app-backend': patch
+---
+
+Added a new `disableConfigInjection` option, which can be used to disable the configuration injection in environments where it can't be used.

plugins/app-backend/src/service/router.ts

@@ -26,8 +26,34 @@ import fs from 'fs-extra';
 export interface RouterOptions {
   config: Config;
   logger: Logger;
+
+  /**
+   * The name of the app package that content should be served from. The same app package should be
+   * added as a dependency to the backend package in order for it to be accessible at runtime.
+   *
+   * In a typical setup with a single app package this would be set to 'app'.
+   */
   appPackageName: string;
+
+  /**
+   * A request handler to handle requests for static content that are not present in the app bundle.
+   *
+   * This can be used to avoid issues with clients on older deployment versions trying to access lazy
+   * loaded content that is no longer present. Typically the requests would fall back to a long-term
+   * object store where all recently deployed versions of the app are present.
+   */
   staticFallbackHandler?: express.Handler;
+
+  /**
+   * Disables the configuration injection. This can be useful if you're running in an environment
+   * with a read-only filesystem, or for some other reason don't want configuration to be injected.
+   *
+   * Note that this will cause the configuration used when building the app bundle to be used, unless
+   * a separate configuration loading strategy is set up.
+   *
+   * This also disables configuration injection though `APP_CONFIG_` environment variables.
+   */
+  disableConfigInjection?: boolean;
 }
 
 export async function createRouter(
@@ -48,13 +74,15 @@ export async function createRouter(
 
   logger.info(`Serving static app content from ${appDistDir}`);
 
-  const appConfigs = await readConfigs({
-    config,
-    appDistDir,
-    env: process.env,
-  });
+  if (!options.disableConfigInjection) {
+    const appConfigs = await readConfigs({
+      config,
+      appDistDir,
+      env: process.env,
+    });
 
-  await injectConfig({ appConfigs, logger, staticDir });
+    await injectConfig({ appConfigs, logger, staticDir });
+  }
 
   const router = Router();