Respect top-level blocks in SSH fleet configuration

Fixes: #3278

Author: un-def

src/dstack/_internal/core/models/fleets.py

@@ -78,17 +78,17 @@ class SSHHostParams(CoreModel):
     ssh_key: Optional[SSHKey] = None
 
     blocks: Annotated[
-        Union[Literal["auto"], int],
+        Optional[Union[Literal["auto"], int]],
         Field(
             description=(
                 "The amount of blocks to split the instance into, a number or `auto`."
                 " `auto` means as many as possible."
                 " The number of GPUs and CPUs must be divisible by the number of blocks."
-                " Defaults to `1`, i.e. do not split"
+                " Defaults to the top-level `blocks` value."
             ),
             ge=1,
         ),
-    ] = 1
+    ] = None
 
     @validator("internal_ip")
     def validate_internal_ip(cls, value):

src/dstack/_internal/server/services/fleets.py

@@ -674,6 +674,7 @@ async def create_fleet_ssh_instance_model(
     spec: FleetSpec,
     ssh_params: SSHParams,
     env: Env,
+    blocks: Union[int, Literal["auto"]],
     instance_num: int,
     host: Union[SSHHostParams, str],
 ) -> InstanceModel:
@@ -684,15 +685,15 @@ async def create_fleet_ssh_instance_model(
         port = ssh_params.port
         proxy_jump = ssh_params.proxy_jump
         internal_ip = None
-        blocks = 1
     else:
         hostname = host.hostname
         ssh_user = host.user or ssh_params.user
         ssh_key = host.ssh_key or ssh_params.ssh_key
         port = host.port or ssh_params.port
         proxy_jump = host.proxy_jump or ssh_params.proxy_jump
         internal_ip = host.internal_ip
-        blocks = host.blocks
+        if host.blocks is not None:
+            blocks = host.blocks
 
     if ssh_user is None or ssh_key is None:
         # This should not be reachable but checked by fleet spec validation
@@ -1042,6 +1043,7 @@ async def _create_fleet(
                     spec=spec,
                     ssh_params=spec.configuration.ssh_config,
                     env=spec.configuration.env,
+                    blocks=spec.configuration.blocks,
                     instance_num=i,
                     host=host,
                 )
@@ -1152,6 +1154,7 @@ async def _update_fleet(
                     spec=spec,
                     ssh_params=spec.configuration.ssh_config,
                     env=spec.configuration.env,
+                    blocks=spec.configuration.blocks,
                     instance_num=instance_num,
                     host=host,
                 )

src/dstack/_internal/server/testing/common.py

@@ -3,7 +3,7 @@
 from collections.abc import Callable
 from contextlib import contextmanager
 from datetime import datetime, timezone
-from typing import Dict, List, Literal, Optional, Union
+from typing import Any, Dict, List, Literal, Optional, Union
 from uuid import UUID
 
 import gpuhunt
@@ -703,6 +703,7 @@ def get_ssh_fleet_configuration(
     hosts: Optional[list[Union[SSHHostParams, str]]] = None,
     network: Optional[str] = None,
     placement: Optional[InstanceGroupPlacement] = None,
+    blocks: Optional[Union[int, Literal["auto"]]] = None,
 ) -> FleetConfiguration:
     if ssh_key is None:
         ssh_key = SSHKey(public="", private=get_private_key_string())
@@ -714,10 +715,14 @@ def get_ssh_fleet_configuration(
         hosts=hosts,
         network=network,
     )
+    optional_properties: dict[str, Any] = {}
+    if blocks is not None:
+        optional_properties["blocks"] = blocks
     return FleetConfiguration(
         name=name,
         ssh_config=ssh_config,
         placement=placement,
+        **optional_properties,
     )
 
 

src/tests/_internal/server/routers/test_fleets.py

@@ -1,6 +1,6 @@
 import json
 from datetime import datetime, timezone
-from typing import Optional, Union
+from typing import Literal, Optional, Union
 from unittest.mock import Mock, patch
 from uuid import uuid4
 
@@ -16,6 +16,7 @@
     FleetConfiguration,
     FleetStatus,
     InstanceGroupPlacement,
+    SSHHostParams,
     SSHParams,
 )
 from dstack._internal.core.models.instances import (
@@ -1178,6 +1179,56 @@ async def test_creates_ssh_fleet(self, test_db, session: AsyncSession, client: A
         instance = res.unique().scalar_one()
         assert instance.remote_connection_info is not None
 
+    @pytest.mark.parametrize(
+        ["top_level_blocks", "host_blocks", "host_type", "expected_blocks"],
+        [
+            pytest.param(None, None, str, 1, id="global-default-string"),
+            pytest.param(None, None, SSHHostParams, 1, id="global-default-object"),
+            pytest.param(4, None, str, 4, id="top-level-int-string"),
+            pytest.param(4, None, SSHHostParams, 4, id="top-level-int-object"),
+            pytest.param("auto", None, str, None, id="top-level-auto-string"),
+            pytest.param("auto", None, SSHHostParams, None, id="top-level-auto-object"),
+            pytest.param("auto", 4, SSHHostParams, 4, id="host-level-int"),
+            pytest.param(4, "auto", SSHHostParams, None, id="host-level-auto"),
+        ],
+    )
+    @pytest.mark.asyncio
+    @pytest.mark.parametrize("test_db", ["sqlite", "postgres"], indirect=True)
+    async def test_creates_ssh_fleet_with_blocks(
+        self,
+        test_db,
+        session: AsyncSession,
+        client: AsyncClient,
+        top_level_blocks: Optional[Union[int, Literal["auto"]]],
+        host_blocks: Optional[Union[int, Literal["auto"]]],
+        host_type: Union[type[str], type[SSHHostParams]],
+        expected_blocks: Optional[int],
+    ):
+        user = await create_user(session, global_role=GlobalRole.USER)
+        project = await create_project(session)
+        await add_project_member(
+            session=session, project=project, user=user, project_role=ProjectRole.USER
+        )
+        if host_type is str:
+            host = "1.1.1.1"
+        elif host_blocks is None:
+            host = SSHHostParams(hostname="1.1.1.1")
+        else:
+            host = SSHHostParams(hostname="1.1.1.1", blocks=host_blocks)
+        conf = get_ssh_fleet_configuration(blocks=top_level_blocks, hosts=[host])
+        spec = get_fleet_spec(conf=conf)
+        response = await client.post(
+            f"/api/project/{project.name}/fleets/apply",
+            headers=get_auth_headers(user.token),
+            json={"plan": {"spec": spec.dict()}, "force": False},
+        )
+        assert response.status_code == 200, response.json()
+        res = await session.execute(select(FleetModel))
+        assert len(res.scalars().all()) == 1
+        res = await session.execute(select(InstanceModel))
+        instance = res.scalar_one()
+        assert instance.total_blocks == expected_blocks
+
     @pytest.mark.asyncio
     @pytest.mark.parametrize("test_db", ["sqlite", "postgres"], indirect=True)
     @freeze_time(datetime(2023, 1, 2, 3, 4, tzinfo=timezone.utc), real_asyncio=True)