refactor due to reviewer's suggestions

sky/cli.py

@@ -4332,7 +4332,7 @@ def serve_status(all: bool, endpoint: bool, service_names: List[str]):
               required=False,
               help='Skip confirmation prompt.')
 @click.option('--replica-id',
-              '-r',
+              '-rid',
               default=None,
               type=int,
               help='Tear down a given replica')
@@ -4379,11 +4379,15 @@ def serve_down(service_names: List[str], all: bool, purge: bool, yes: bool,
         raise click.UsageError(
             'Can only specify one of SERVICE_NAMES or --all. '
             f'Provided {argument_str!r}.')
+
     replica_id_is_defined = replica_id is not None
-    if replica_id_is_defined and len(service_names) != 1:
-        raise click.UsageError(
-            'Must specify one and only one service when replica ID is '
-            'specified.')
+    if replica_id_is_defined:
+        if len(service_names) != 1:
+            raise click.UsageError('The --replica-id option can only be used '
+                                   'with a single service name.')
+        if all:
+            raise click.UsageError('The --replica-id option cannot be used '
+                                   'with the --all option.')
 
     backend_utils.is_controller_accessible(
         controller=controller_utils.Controllers.SKY_SERVE_CONTROLLER,

sky/serve/controller.py

@@ -180,38 +180,32 @@ async def terminate_replica(request: fastapi.Request):
             request_data = await request.json()
             try:
                 replica_id = request_data.get('replica_id')
-                if replica_id is None:
-                    return {
-                        'code': 400,
-                        'message': 'Error: replica ID is not specified.'
-                    }
+                assert isinstance(replica_id,
+                                  int), 'Error: replica ID is not specified.'
                 purge = request_data.get('purge')
-                if purge is None:
-                    return {
-                        'code': 400,
-                        'message': 'Error: purge is not specified.'
-                    }
+                assert isinstance(purge, bool), 'Error: purge is not specified.'
                 replica_info = serve_state.get_replica_info_from_id(
                     self._service_name, replica_id)
-                if replica_info is None:
-                    return {
-                        'code': 400,
-                        'message': f'Error: replica {replica_id} '
-                                   f'does not exist.'
-                    }
+                assert replica_info is not None, f'Error: replica ' \
+                                                 f'{replica_id} does not exist.'
 
                 if purge:
                     return self._purge_replica(replica_info)
 
                 logger.info(f'Terminating replica {replica_id}...')
                 self._replica_manager.scale_down(replica_id)
-                return {'message': f'Success terminating replica {replica_id}.'}
+                return fastapi.Response(
+                    status_code=200,
+                    content={
+                        'message': f'Success terminating replica {replica_id}.'
+                    })
 
             except Exception as e:  # pylint: disable=broad-except
                 error_message = (f'Error in terminate_replica: '
                                  f'{common_utils.format_exception(e)}')
                 logger.error(error_message)
-                return {'code': 500, 'message': error_message}
+                return fastapi.Response(status_code=500,
+                                        content={'message': error_message})
 
         @self._app.on_event('startup')
         def configure_logger():

sky/serve/core.py

@@ -328,7 +328,8 @@ def update(
         'Service controller is stopped. There is no service to update. '
         f'To spin up a new service, use {backend_utils.BOLD}'
         f'sky serve up{backend_utils.RESET_BOLD}',
-        non_existent_message='To spin up a new service, '
+        non_existent_message='Service does not exist. '
+        'To spin up a new service, '
         f'use {backend_utils.BOLD}sky serve up{backend_utils.RESET_BOLD}',
     )
 
@@ -521,8 +522,8 @@ def terminate_replica(service_name: str, replica_id: int, purge: bool) -> None:
         controller=controller_utils.Controllers.SKY_SERVE_CONTROLLER,
         stopped_message=
         'No service is running now. Please spin up a service first.',
-        non_existent_message='To spin up a new service, '
-        f'use {backend_utils.BOLD}sky serve up{backend_utils.RESET_BOLD}',
+        non_existent_message='No service is running now. '
+        'Please spin up a service first.',
     )
 
     backend = backend_utils.get_backend_from_handle(handle)

sky/serve/serve_utils.py

@@ -313,8 +313,12 @@ def terminate_replica(service_name: str, replica_id: int, purge: bool) -> str:
     service_status = _get_service_status(service_name)
     if service_status is None:
         raise ValueError(f'Service {service_name!r} does not exist.')
-    controller_port = service_status['controller_port']
+    replica_info = serve_state.get_replica_info_from_id(service_name,
+                                                        replica_id)
+    if replica_info is None:
+        raise ValueError(f'Replica {replica_id} does not exist.')
 
+    controller_port = service_status['controller_port']
     resp = requests.post(
         _CONTROLLER_URL.format(CONTROLLER_PORT=controller_port) +
         '/controller/terminate_replica',