set spark driver host for user's spawner container

src/jupyterhub_config/custom_docker_spawner.py

@@ -86,12 +86,14 @@ def _configure_environment(self, user_dir: Path, user_env_dir: Path, username: s
         Configure the environment variables for the user's session, including
         the PATH and PYTHONPATH to use the virtual environment.
         """
-
         self.environment.update({key: value for key, value in os.environ.items() if key not in self.environment})
 
         self.environment['JUPYTER_MODE'] = 'jupyterhub-singleuser'
         self.environment['JUPYTERHUB_ADMIN'] = self.user.admin
 
+        self.log.info(f'Setting spark driver host to {self.container_name}')
+        self.environment['SPARK_DRIVER_HOST'] = self.container_name
+
         self.environment['HOME'] = str(user_dir)
         self.environment['PATH'] = f"{user_env_dir}/bin:{os.environ['PATH']}"
         self.environment['VIRTUAL_ENV'] = str(user_env_dir)