feat(db-config): support a ensureExists config option

Signed-off-by: Phil Kuang <pkuang@factset.com>

.changeset/angry-ghosts-report.md

@@ -0,0 +1,16 @@
+---
+'@backstage/backend-common': patch
+---
+
+Support a `ensureExists` config option to skip ensuring a configured database exists. This allows deployment scenarios where
+limited permissions are given for provisioned databases without privileges to create new databases. If set to `false`, the
+database connection will not be validated prior to use which means the backend will not attempt to create the database if it
+doesn't exist. You can configure this in your app-config.yaml:
+
+```yaml
+backend:
+  database:
+    ensureExists: false
+```
+
+This defaults to `true` if unspecified. You can also configure this per plugin connection and will override the base option.

packages/backend-common/config.d.ts

@@ -64,6 +64,11 @@ export interface Config {
       connection: string | object;
       /** Database name prefix override */
       prefix?: string;
+      /**
+       * Whether to ensure the given database exists by creating it if it does not.
+       * Defaults to true if unspecified.
+       */
+      ensureExists?: boolean;
       /** Plugin specific database configuration and client override */
       plugin?: {
         [pluginId: string]: {
@@ -74,6 +79,11 @@ export interface Config {
            * @secret
            */
           connection?: string | object;
+          /**
+           * Whether to ensure the given database exists by creating it if it does not.
+           * Defaults to base config if unspecified.
+           */
+          ensureExists?: boolean;
         };
       };
     };

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

@@ -128,6 +128,14 @@ export class DatabaseManager {
     };
   }
 
+  private getEnsureExistsConfig(pluginId: string): boolean {
+    const baseConfig = this.config.getOptionalBoolean('ensureExists') ?? true;
+    return (
+      this.config.getOptionalBoolean(`${pluginPath(pluginId)}.ensureExists`) ??
+      baseConfig
+    );
+  }
+
   /**
    * Provides a Knex connection plugin config by combining base and plugin config.
    *
@@ -203,13 +211,15 @@ export class DatabaseManager {
       this.getConfigForPlugin(pluginId) as JsonObject,
     );
 
-    const databaseName = this.getDatabaseName(pluginId);
-    try {
-      await ensureDatabaseExists(pluginConfig, databaseName);
-    } catch (error) {
-      throw new Error(
-        `Failed to connect to the database to make sure that '${databaseName}' exists, ${error}`,
-      );
+    if (this.getEnsureExistsConfig(pluginId)) {
+      const databaseName = this.getDatabaseName(pluginId);
+      try {
+        await ensureDatabaseExists(pluginConfig, databaseName);
+      } catch (error) {
+        throw new Error(
+          `Failed to connect to the database to make sure that '${databaseName}' exists, ${error}`,
+        );
+      }
     }
 
     return createDatabaseClient(