feat: added disable config watching flag

Signed-off-by: Antonio Musolino <antoniomusolino007@gmail.com>

.changeset/stale-eagles-reply.md

@@ -0,0 +1,6 @@
+---
+'@backstage/config-loader': patch
+'@backstage/backend-app-api': patch
+---
+
+Added `watch` option to configuration loaders that can be used to disable file watching by setting it to `false`.

packages/backend-app-api/api-report.md

@@ -190,6 +190,7 @@ export function loadBackendConfig(options: {
   remote?: LoadConfigOptionsRemote;
   argv: string[];
   additionalConfigs?: AppConfig[];
+  watch?: boolean;
 }): Promise<{
   config: Config;
 }>;

packages/backend-app-api/src/config/config.ts

@@ -72,6 +72,7 @@ export async function loadBackendConfig(options: {
   remote?: LoadConfigOptionsRemote;
   argv: string[];
   additionalConfigs?: AppConfig[];
+  watch?: boolean;
 }): Promise<{ config: Config }> {
   const args = parseArgs(options.argv);
 
@@ -89,30 +90,35 @@ export async function loadBackendConfig(options: {
     configRoot: paths.targetRoot,
     configTargets: configTargets,
     remote: options.remote,
-    watch: {
-      onChange(newConfigs) {
-        console.info(
-          `Reloaded config from ${newConfigs.map(c => c.context).join(', ')}`,
-        );
-        const configsToMerge = [...newConfigs];
-        if (options.additionalConfigs) {
-          configsToMerge.push(...options.additionalConfigs);
-        }
-        config.setConfig(ConfigReader.fromConfigs(configsToMerge));
-      },
-      stopSignal: new Promise(resolve => {
-        if (currentCancelFunc) {
-          currentCancelFunc();
-        }
-        currentCancelFunc = resolve;
+    watch:
+      options.watch ?? true
+        ? {
+            onChange(newConfigs) {
+              console.info(
+                `Reloaded config from ${newConfigs
+                  .map(c => c.context)
+                  .join(', ')}`,
+              );
+              const configsToMerge = [...newConfigs];
+              if (options.additionalConfigs) {
+                configsToMerge.push(...options.additionalConfigs);
+              }
+              config.setConfig(ConfigReader.fromConfigs(configsToMerge));
+            },
+            stopSignal: new Promise(resolve => {
+              if (currentCancelFunc) {
+                currentCancelFunc();
+              }
+              currentCancelFunc = resolve;
 
-        // TODO(Rugvip): We keep this here for now to avoid breaking the old system
-        //               since this is re-used in backend-common
-        if (module.hot) {
-          module.hot.addDisposeHandler(resolve);
-        }
-      }),
-    },
+              // TODO(Rugvip): We keep this here for now to avoid breaking the old system
+              //               since this is re-used in backend-common
+              if (module.hot) {
+                module.hot.addDisposeHandler(resolve);
+              }
+            }),
+          }
+        : undefined,
   });
   console.info(
     `Loaded config from ${appConfigs.map(c => c.context).join(', ')}`,

packages/backend-common/api-report.md

@@ -552,6 +552,7 @@ export function loadBackendConfig(options: {
   remote?: LoadConfigOptionsRemote;
   additionalConfigs?: AppConfig[];
   argv: string[];
+  watch?: boolean;
 }): Promise<Config>;
 
 // @public (undocumented)

packages/backend-common/src/config.ts

@@ -36,6 +36,7 @@ export async function loadBackendConfig(options: {
   remote?: LoadConfigOptionsRemote;
   additionalConfigs?: AppConfig[];
   argv: string[];
+  watch?: boolean;
 }): Promise<Config> {
   const secretEnumerator = await createConfigSecretEnumerator({
     logger: options.logger,

packages/config-loader/api-report.md

@@ -27,6 +27,8 @@ export interface BaseConfigSourcesOptions {
   rootDir?: string;
   // (undocumented)
   substitutionFunc?: EnvFunc;
+  // (undocumented)
+  watch?: boolean;
 }
 
 // @public
@@ -142,6 +144,7 @@ export class FileConfigSource implements ConfigSource {
 export interface FileConfigSourceOptions {
   path: string;
   substitutionFunc?: EnvFunc;
+  watch?: boolean;
 }
 
 // @public @deprecated

packages/config-loader/src/loader.ts

@@ -107,6 +107,7 @@ export async function loadConfig(
     remote: options.remote && {
       reloadInterval: { seconds: options.remote.reloadIntervalSeconds },
     },
+    watch: Boolean(options.watch),
     rootDir: options.configRoot,
     argv: options.configTargets.flatMap(t => [
       '--config',

packages/config-loader/src/sources/ConfigSources.ts

@@ -71,6 +71,7 @@ export interface ClosableConfig extends Config {
  * @public
  */
 export interface BaseConfigSourcesOptions {
+  watch?: boolean;
   rootDir?: string;
   remote?: Pick<RemoteConfigSourceOptions, 'reloadInterval'>;
   substitutionFunc?: SubstitutionFunc;
@@ -159,6 +160,7 @@ export class ConfigSources {
         });
       }
       return FileConfigSource.create({
+        watch: options.watch,
         path: arg.target,
         substitutionFunc: options.substitutionFunc,
       });
@@ -170,6 +172,7 @@ export class ConfigSources {
 
       argSources.push(
         FileConfigSource.create({
+          watch: options.watch,
           path: defaultPath,
           substitutionFunc: options.substitutionFunc,
         }),
@@ -177,6 +180,7 @@ export class ConfigSources {
       if (fs.pathExistsSync(localPath)) {
         argSources.push(
           FileConfigSource.create({
+            watch: options.watch,
             path: localPath,
             substitutionFunc: options.substitutionFunc,
           }),

packages/config-loader/src/sources/FileConfigSource.ts

@@ -39,6 +39,11 @@ export interface FileConfigSourceOptions {
    */
   path: string;
 
+  /**
+   * Enable watching file
+   */
+  watch?: boolean;
+
   /**
    * A substitution function to use instead of the default environment substitution.
    */
@@ -89,10 +94,12 @@ export class FileConfigSource implements ConfigSource {
 
   readonly #path: string;
   readonly #substitutionFunc?: SubstitutionFunc;
+  readonly #watch?: boolean;
 
   private constructor(options: FileConfigSourceOptions) {
     this.#path = options.path;
     this.#substitutionFunc = options.substitutionFunc;
+    this.#watch = options.watch ?? true;
   }
 
   // Work is duplicated across each read, in practice that should not
@@ -104,20 +111,27 @@ export class FileConfigSource implements ConfigSource {
     const signal = options?.signal;
     const configFileName = basename(this.#path);
 
-    // Keep track of watched paths, since this is simpler than resetting the watcher
-    const watchedPaths = new Array<string>();
-    const watcher = chokidar.watch(this.#path, {
-      usePolling: process.env.NODE_ENV === 'test',
-    });
+    let watchedPaths: Array<string> | null = null;
+    let watcher: FSWatcher | null = null;
+
+    if (this.#watch) {
+      // Keep track of watched paths, since this is simpler than resetting the watcher
+      watchedPaths = new Array<string>();
+      watcher = chokidar.watch(this.#path, {
+        usePolling: process.env.NODE_ENV === 'test',
+      });
+    }
 
     const dir = dirname(this.#path);
     const transformer = createConfigTransformer({
       substitutionFunc: this.#substitutionFunc,
       readFile: async path => {
         const fullPath = resolvePath(dir, path);
-        // Any files discovered while reading this config should be watched too
-        watcher.add(fullPath);
-        watchedPaths.push(fullPath);
+        if (watcher && watchedPaths) {
+          // Any files discovered while reading this config should be watched too
+          watcher.add(fullPath);
+          watchedPaths.push(fullPath);
+        }
 
         const data = await readFile(fullPath);
         if (data === undefined) {
@@ -131,12 +145,15 @@ export class FileConfigSource implements ConfigSource {
 
     // This is the entry point for reading the file, called initially and on change
     const readConfigFile = async (): Promise<ConfigSourceData[]> => {
-      // We clear the watched files every time we initiate a new read
-      watcher.unwatch(watchedPaths);
-      watchedPaths.length = 0;
+      if (watcher && watchedPaths) {
+        // We clear the watched files every time we initiate a new read
+        watcher.unwatch(watchedPaths);
+        watchedPaths.length = 0;
+
+        watcher.add(this.#path);
+        watchedPaths.push(this.#path);
+      }
 
-      watcher.add(this.#path);
-      watchedPaths.push(this.#path);
       const content = await readFile(this.#path);
       if (content === undefined) {
         throw new NotFoundError(`Config file "${this.#path}" does not exist`);
@@ -157,18 +174,20 @@ export class FileConfigSource implements ConfigSource {
 
     const onAbort = () => {
       signal?.removeEventListener('abort', onAbort);
-      watcher.close();
+      if (watcher) watcher.close();
     };
     signal?.addEventListener('abort', onAbort);
 
     yield { configs: await readConfigFile() };
 
-    for (;;) {
-      const event = await this.#waitForEvent(watcher, signal);
-      if (event === 'abort') {
-        return;
+    if (watcher) {
+      for (;;) {
+        const event = await this.#waitForEvent(watcher, signal);
+        if (event === 'abort') {
+          return;
+        }
+        yield { configs: await readConfigFile() };
       }
-      yield { configs: await readConfigFile() };
     }
   }