do not create duplicate db connection pools in the old backend

Signed-off-by: Fredrik Adelöw <freben@gmail.com>

.changeset/angry-ghosts-brush.md

@@ -0,0 +1,13 @@
+---
+'@backstage/create-app': patch
+---
+
+Updated the backend template to no longer create duplicate connection pools to plugins that use the task scheduler.
+
+To apply this change in your own repository, perform the following small update:
+
+```diff
+// in packages/backend/src/index.ts
+-  const taskScheduler = TaskScheduler.fromConfig(config);
++  const taskScheduler = TaskScheduler.fromConfig(config, { databaseManager });
+```

.changeset/thin-ladybugs-lick.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-common': patch
+---
+
+Minor internal refactor

packages/backend-common/src/database/DatabaseManager.ts

@@ -56,13 +56,14 @@ export type DatabaseManagerOptions = {
 /**
  * Manages database connections for Backstage backend plugins.
  *
+ * @public
+ * @remarks
+ *
  * The database manager allows the user to set connection and client settings on
  * a per pluginId basis by defining a database config block under
  * `plugin.<pluginId>` in addition to top level defaults. Optionally, a user may
  * set `prefix` which is used to prefix generated database names if config is
  * not provided.
- *
- * @public
  */
 export class DatabaseManager {
   /**
@@ -105,17 +106,9 @@ export class DatabaseManager {
       pluginMetadata: PluginMetadataService;
     },
   ): PluginDatabaseManager {
-    const _this = this;
-
-    return {
-      getClient(): Promise<Knex> {
-        return _this.getDatabase(pluginId, deps);
-      },
-      migrations: {
-        skip: false,
-        ..._this.options?.migrations,
-      },
-    };
+    const getClient = () => this.getDatabase(pluginId, deps);
+    const migrations = { skip: false, ...this.options?.migrations };
+    return { getClient, migrations };
   }
 
   /**

packages/backend/src/index.ts

@@ -93,7 +93,7 @@ function makeCreateEnv(config: Config) {
   });
   const databaseManager = DatabaseManager.fromConfig(config, { logger: root });
   const cacheManager = CacheManager.fromConfig(config);
-  const taskScheduler = TaskScheduler.fromConfig(config);
+  const taskScheduler = TaskScheduler.fromConfig(config, { databaseManager });
   const identity = DefaultIdentityClient.create({
     discovery,
   });

packages/create-app/templates/default-app/packages/backend/src/index.ts

@@ -39,7 +39,7 @@ function makeCreateEnv(config: Config) {
   const cacheManager = CacheManager.fromConfig(config);
   const databaseManager = DatabaseManager.fromConfig(config, { logger: root });
   const tokenManager = ServerTokenManager.noop();
-  const taskScheduler = TaskScheduler.fromConfig(config);
+  const taskScheduler = TaskScheduler.fromConfig(config, { databaseManager });
 
   const identity = DefaultIdentityClient.create({
     discovery,