Prevent dstack Sky gateway deletion

Author: r4victor

src/dstack/_internal/server/background/pipeline_tasks/gateways.py

@@ -9,6 +9,7 @@
 
 from dstack._internal.core.backends.base.compute import ComputeWithGatewaySupport
 from dstack._internal.core.errors import BackendError, BackendNotAvailable
+from dstack._internal.core.models.backends.base import BackendType
 from dstack._internal.core.models.gateways import GatewayStatus
 from dstack._internal.server.background.pipeline_tasks.base import (
     Fetcher,
@@ -512,6 +513,7 @@ class _DeletedResult:
 
 
 async def _process_to_be_deleted_gateway(gateway_model: GatewayModel) -> _DeletedResult:
+    assert gateway_model.backend.type != BackendType.DSTACK
     backend = await backends_services.get_project_backend_by_type_or_error(
         project=gateway_model.project, backend_type=gateway_model.backend.type
     )

src/dstack/_internal/server/services/gateways/__init__.py

@@ -10,7 +10,7 @@
 import httpx
 from sqlalchemy import func, select, update
 from sqlalchemy.ext.asyncio import AsyncSession
-from sqlalchemy.orm import selectinload
+from sqlalchemy.orm import joinedload, selectinload
 
 import dstack._internal.utils.random_names as random_names
 from dstack._internal.core.backends.base.compute import (
@@ -42,6 +42,7 @@
 from dstack._internal.server import settings
 from dstack._internal.server.db import get_db, is_db_postgres, is_db_sqlite
 from dstack._internal.server.models import (
+    BackendModel,
     GatewayComputeModel,
     GatewayModel,
     ProjectModel,
@@ -329,9 +330,10 @@ async def _delete_gateways_pipeline(
                 GatewayModel.project_id == project.id,
                 GatewayModel.lock_expires_at.is_(None),
             )
-            .execution_options(populate_existing=True)
+            .options(joinedload(GatewayModel.backend).load_only(BackendModel.type))
             .order_by(GatewayModel.id)  # take locks in order
-            .with_for_update(key_share=True, nowait=True)
+            .with_for_update(key_share=True, nowait=True, of=GatewayModel)
+            .execution_options(populate_existing=True)
         )
         gateway_models = res.scalars().all()
         if len(gateway_models) != len(gateways_ids):
@@ -340,6 +342,9 @@ async def _delete_gateways_pipeline(
             raise ServerClientError(
                 "Failed to delete gateways: gateways are being processed currently. Try again later."
             )
+        for gateway_model in gateway_models:
+            if gateway_model.backend.type == BackendType.DSTACK:
+                raise ServerClientError("Cannot delete dstack Sky gateway")
         for gateway_model in gateway_models:
             if not gateway_model.to_be_deleted:
                 gateway_model.to_be_deleted = True