When the catalog entity couldn't be found the /sync endpoint would return with a 404 and a JSON response which was not expected by the event-stream fetch on the frontend. This causes the client to continuously make requests to the /sync endpoint.

Signed-off-by: Alex Lorenzi <alorenzi@spotify.com>

.changeset/good-flowers-promise.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-techdocs-backend': patch
+---
+
+Modified response when catalog entity isn't found to resolve issue where `/sync` endpoint was continuously called

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

@@ -242,14 +242,14 @@ export async function createRouter(
       targetPluginId: 'catalog',
     });
 
-    const entity = await entityLoader.load({ kind, namespace, name }, token);
-
-    if (!entity?.metadata?.uid) {
-      throw new NotFoundError('Entity metadata UID missing');
-    }
-
     const responseHandler: DocsSynchronizerSyncOpts = createEventStream(res);
 
+    const entity = await entityLoader.load({ kind, namespace, name }, token);
+    if (!entity?.metadata?.uid) {
+      responseHandler.error(new NotFoundError('Entity metadata UID missing'));
+      return;
+    }
+
     // By default, techdocs-backend will only try to build documentation for an entity if techdocs.builder is set to
     // 'local'. If set to 'external', it will assume that an external process (e.g. CI/CD pipeline
     // of the repository) is responsible for building and publishing documentation to the storage provider.