Fix Vast.ai offer order in dstack offer --fleet

Order by score rather than by price, the same way
offers are already ordered in apply plans and
`dstack offer` without `--fleet`.

Author: jvstme

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

@@ -1,5 +1,4 @@
 import asyncio
-import heapq
 import json
 import time
 from collections.abc import Iterable, Iterator
@@ -43,6 +42,7 @@
 from dstack._internal.core.models.runs import Requirements
 from dstack._internal.server import settings
 from dstack._internal.server.models import BackendModel, DecryptedString, ProjectModel
+from dstack._internal.server.services.offers import merge_offer_iterables
 from dstack._internal.settings import LOCAL_BACKEND_ENABLED
 from dstack._internal.utils.common import run_async
 from dstack._internal.utils.logging import get_logger
@@ -459,7 +459,7 @@ async def get_backend_offers(
     backends: List[Backend],
     requirements: Requirements,
     exclude_not_available: bool = False,
-) -> Iterator[Tuple[Backend, InstanceOfferWithAvailability]]:
+) -> Iterable[Tuple[Backend, InstanceOfferWithAvailability]]:
     """
     Yields backend offers satisfying `requirements` sorted by price.
     """
@@ -474,7 +474,7 @@ def get_filtered_offers_with_backends(
 
     logger.debug("Requesting instance offers from backends: %s", [b.TYPE.value for b in backends])
     tasks = [run_async(get_offers_tracked, backend, requirements) for backend in backends]
-    offers_by_backend = []
+    offers_by_backend: list[Iterable[tuple[Backend, InstanceOfferWithAvailability]]] = []
     for backend, result in zip(backends, await asyncio.gather(*tasks, return_exceptions=True)):
         if isinstance(result, BackendError):
             logger.warning(
@@ -491,9 +491,7 @@ def get_filtered_offers_with_backends(
             )
             continue
         offers_by_backend.append(get_filtered_offers_with_backends(backend, result))
-    # Merge preserving order for every backend.
-    offers = heapq.merge(*offers_by_backend, key=lambda i: i[1].price)
-    return offers
+    return merge_offer_iterables(*offers_by_backend)
 
 
 def check_backend_type_available(backend_type: BackendType):

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

@@ -1,6 +1,7 @@
+import heapq
 import itertools
 from collections.abc import Container, Iterable, Iterator
-from typing import List, Literal, Optional, Tuple, Union
+from typing import List, Literal, Optional, Tuple, TypeVar, Union
 
 import gpuhunt
 
@@ -116,6 +117,21 @@ async def get_offers_by_requirements(
     return sorted(offers, key=lambda i: not i[1].availability.is_available())
 
 
+T = TypeVar("T")
+
+
+def merge_offer_iterables(
+    *iterables: Iterable[tuple[T, InstanceOfferWithAvailability]],
+) -> Iterable[tuple[T, InstanceOfferWithAvailability]]:
+    """
+    Merge offers from different sources (e.g., different backends, different fleets).
+
+    Some backends produce offers that are not sorted by price (e.g., `vastai` sorts by pod score).
+    That backend-specific order is preserved.
+    """
+    return heapq.merge(*iterables, key=lambda i: i[1].price)
+
+
 def is_divisible_into_blocks(
     cpu_count: int, gpu_count: int, blocks: Union[int, Literal["auto"]]
 ) -> tuple[bool, int]:

src/dstack/_internal/server/services/runs/plan.py

@@ -52,7 +52,10 @@
     is_multinode_job,
     remove_job_spec_sensitive_info,
 )
-from dstack._internal.server.services.offers import get_offers_by_requirements
+from dstack._internal.server.services.offers import (
+    get_offers_by_requirements,
+    merge_offer_iterables,
+)
 from dstack._internal.server.services.requirements.combine import (
     combine_fleet_and_run_profiles,
     combine_fleet_and_run_requirements,
@@ -711,11 +714,10 @@ async def get_backend_offers_in_run_candidate_fleets(
         run_model=None,
         run_spec=run_spec,
     )
-    deduplicated_backend_offers: dict[
-        Hashable,
-        tuple[Backend, InstanceOfferWithAvailability],
-    ] = {}
+    seen_offer_identities = set()
+    offers: list[tuple[Backend, InstanceOfferWithAvailability]] = []
     for candidate_fleet_model in candidate_fleet_models:
+        offers_from_fleet = []
         for backend, offer in await _get_backend_offers_in_fleet(
             project=project,
             fleet_model=candidate_fleet_model,
@@ -724,13 +726,12 @@ async def get_backend_offers_in_run_candidate_fleets(
             volumes=volumes,
             max_offers=max_offers_per_fleet,
         ):
-            deduplicated_backend_offers.setdefault(
-                _get_backend_offer_identity(offer),
-                (backend, offer),
-            )
-    backend_offers = list(deduplicated_backend_offers.values())
-    backend_offers.sort(key=lambda offer: offer[1].price)
-    return backend_offers
+            offer_identity = _get_backend_offer_identity(offer)
+            if offer_identity not in seen_offer_identities:
+                offers_from_fleet.append((backend, offer))
+                seen_offer_identities.add(offer_identity)
+        offers = list(merge_offer_iterables(offers, offers_from_fleet))
+    return offers
 
 
 async def _get_offers_in_run_candidate_fleets(

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

@@ -751,11 +751,13 @@ def get_fleet_configuration(
     name: str = "test-fleet",
     nodes: FleetNodesSpec = FleetNodesSpec(min=1, target=1, max=1),
     placement: Optional[InstanceGroupPlacement] = None,
+    backends: Optional[list[BackendType]] = None,
 ) -> FleetConfiguration:
     return FleetConfiguration(
         name=name,
         nodes=nodes,
         placement=placement,
+        backends=backends,
     )
 
 

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

@@ -21,6 +21,7 @@
     ScalingSpec,
     ServiceConfiguration,
     TaskConfiguration,
+    parse_run_configuration,
 )
 from dstack._internal.core.models.fleets import FleetNodesSpec
 from dstack._internal.core.models.gateways import GatewayStatus
@@ -66,6 +67,7 @@
     create_run,
     create_user,
     get_auth_headers,
+    get_fleet_configuration,
     get_fleet_spec,
     get_instance_offer_with_availability,
     get_job_provisioning_data,
@@ -1916,6 +1918,152 @@ async def test_returns_no_offers_if_imported_fleet_specified_without_project_pre
         assert response_json["project_name"] == "importer"
         assert len(response_json["job_plans"][0]["offers"]) == 0
 
+    @pytest.mark.asyncio
+    @pytest.mark.parametrize("test_db", ["sqlite", "postgres"], indirect=True)
+    @pytest.mark.parametrize(
+        "configuration",
+        [
+            pytest.param({"type": "dev-environment"}, id="regular-configuration"),
+            pytest.param(
+                {"type": "task", "commands": [":"], "image": "scratch"},
+                id="special-configuration-used-by-dstack-offer-cli-command",
+            ),
+            pytest.param(
+                {"type": "task", "commands": [":"], "image": "scratch", "fleets": ["test-fleet"]},
+                id="special-configuration-used-by-dstack-offer-cli-command-with-fleets",  # --fleet
+            ),
+        ],
+    )
+    async def test_preserves_backend_specific_offer_order(
+        self,
+        test_db,
+        session: AsyncSession,
+        client: AsyncClient,
+        configuration: dict,
+    ) -> None:
+        user = await create_user(session=session, global_role=GlobalRole.USER)
+        project = await create_project(session=session, owner=user)
+        await add_project_member(
+            session=session,
+            project=project,
+            user=user,
+            project_role=ProjectRole.USER,
+        )
+        repo = await create_repo(session=session, project_id=project.id)
+        await create_fleet(
+            session=session,
+            project=project,
+            spec=get_fleet_spec(conf=get_fleet_configuration(name="test-fleet")),
+        )
+
+        run_spec = get_run_spec(
+            repo_id=repo.name, configuration=parse_run_configuration(configuration)
+        )
+        body = {"run_spec": run_spec.dict()}
+
+        backend_mock_aws = Mock()
+        backend_mock_aws.TYPE = BackendType.AWS
+        backend_mock_aws.compute.return_value.get_offers.return_value = [
+            get_instance_offer_with_availability(backend=BackendType.AWS, price=1.0),
+            get_instance_offer_with_availability(backend=BackendType.AWS, price=4.0),
+        ]
+        backend_mock_vastai = Mock()
+        backend_mock_vastai.TYPE = BackendType.VASTAI
+        backend_mock_vastai.compute.return_value.get_offers.return_value = [
+            # not ordered by price - custom order should be preserved
+            get_instance_offer_with_availability(backend=BackendType.VASTAI, price=3.0),
+            get_instance_offer_with_availability(backend=BackendType.VASTAI, price=2.0),
+        ]
+
+        with patch("dstack._internal.server.services.backends.get_project_backends") as m:
+            m.return_value = [backend_mock_aws, backend_mock_vastai]
+            response = await client.post(
+                f"/api/project/{project.name}/runs/get_plan",
+                headers=get_auth_headers(user.token),
+                json=body,
+            )
+
+        assert response.status_code == 200, response.json()
+        offers = [(o["backend"], o["price"]) for o in response.json()["job_plans"][0]["offers"]]
+        expected_offers = [
+            (BackendType.AWS.value, 1.0),
+            (BackendType.VASTAI.value, 3.0),
+            (BackendType.VASTAI.value, 2.0),
+            (BackendType.AWS.value, 4.0),
+        ]
+        assert offers == expected_offers
+
+    @pytest.mark.asyncio
+    @pytest.mark.parametrize("test_db", ["sqlite", "postgres"], indirect=True)
+    async def test_offer_cli_preserves_backend_specific_offer_order_across_fleets(
+        self, test_db, session: AsyncSession, client: AsyncClient
+    ) -> None:
+        user = await create_user(session=session, global_role=GlobalRole.USER)
+        project = await create_project(session=session, owner=user)
+        await add_project_member(
+            session=session,
+            project=project,
+            user=user,
+            project_role=ProjectRole.USER,
+        )
+        repo = await create_repo(session=session, project_id=project.id)
+        await create_fleet(
+            session=session,
+            project=project,
+            spec=get_fleet_spec(
+                conf=get_fleet_configuration(name="fleet-aws", backends=[BackendType.AWS])
+            ),
+        )
+        await create_fleet(
+            session=session,
+            project=project,
+            spec=get_fleet_spec(
+                conf=get_fleet_configuration(name="fleet-vastai", backends=[BackendType.VASTAI])
+            ),
+        )
+
+        run_spec = get_run_spec(
+            repo_id=repo.name,
+            configuration=TaskConfiguration(
+                commands=[":"],
+                image="scratch",
+                fleets=["fleet-aws", "fleet-vastai"],
+            ),
+        )
+        body = {"run_spec": run_spec.dict()}
+
+        backend_mock_aws = Mock()
+        backend_mock_aws.TYPE = BackendType.AWS
+        backend_mock_aws.compute.return_value.get_offers.return_value = [
+            get_instance_offer_with_availability(backend=BackendType.AWS, price=1.0),
+            get_instance_offer_with_availability(backend=BackendType.AWS, price=4.0),
+        ]
+        backend_mock_vastai = Mock()
+        backend_mock_vastai.TYPE = BackendType.VASTAI
+        backend_mock_vastai.compute.return_value.get_offers.return_value = [
+            # not ordered by price - custom order should be preserved
+            get_instance_offer_with_availability(backend=BackendType.VASTAI, price=3.0),
+            get_instance_offer_with_availability(backend=BackendType.VASTAI, price=2.0),
+        ]
+
+        with patch("dstack._internal.server.services.backends.get_project_backends") as m:
+            m.return_value = [backend_mock_aws, backend_mock_vastai]
+            response = await client.post(
+                f"/api/project/{project.name}/runs/get_plan",
+                headers=get_auth_headers(user.token),
+                json=body,
+            )
+
+        assert response.status_code == 200, response.json()
+        offers = [(o["backend"], o["price"]) for o in response.json()["job_plans"][0]["offers"]]
+        expected_offers = [
+            (BackendType.AWS.value, 1.0),
+            (BackendType.VASTAI.value, 3.0),
+            (BackendType.VASTAI.value, 2.0),
+            (BackendType.AWS.value, 4.0),
+        ]
+        assert offers == expected_offers
+
     @pytest.mark.asyncio
     @pytest.mark.parametrize("test_db", ["sqlite", "postgres"], indirect=True)
     async def test_offer_cli_returns_offers_from_all_specified_fleets(