ISD-1516 Remove is_leader check when running db migration

src/charm.py

@@ -534,20 +534,24 @@ def _execute_migrations(self) -> None:
         if not self._are_relations_ready() or not container.can_connect():
             logger.info("Not ready to execute migrations")
             return
-        if self.model.unit.is_leader():
-            env_settings = self._create_discourse_environment_settings()
-            self.model.unit.status = MaintenanceStatus("Executing migrations")
-            try:
-                migration_process: ExecProcess = container.exec(
-                    [f"{DISCOURSE_PATH}/bin/bundle", "exec", "rake", "--trace", "db:migrate"],
-                    environment=env_settings,
-                    working_dir=DISCOURSE_PATH,
-                    user=CONTAINER_APP_USERNAME,
-                )
-                migration_process.wait_output()
-            except ExecError as cmd_err:
-                logger.exception("Executing migrations failed with code %d.", cmd_err.exit_code)
-                raise
+        env_settings = self._create_discourse_environment_settings()
+        self.model.unit.status = MaintenanceStatus("Executing migrations")
+        # The rails migration task is idempotent and concurrent-safe, from
+        # https://stackoverflow.com/questions/17815769/are-rake-dbcreate-and-rake-dbmigrate-idempotent
+        # and https://github.com/rails/rails/pull/22122
+        # Thus it's safe to run this task on all units to
+        # avoid complications with how juju schedules charm upgrades
+        try:
+            migration_process: ExecProcess = container.exec(
+                [f"{DISCOURSE_PATH}/bin/bundle", "exec", "rake", "--trace", "db:migrate"],
+                environment=env_settings,
+                working_dir=DISCOURSE_PATH,
+                user=CONTAINER_APP_USERNAME,
+            )
+            migration_process.wait_output()
+        except ExecError as cmd_err:
+            logger.exception("Executing migrations failed with code %d.", cmd_err.exit_code)
+            raise
 
     def _compile_assets(self) -> None:
         container = self.unit.get_container(CONTAINER_NAME)