exo-explore/exo · error · HTTPException

Expected exactly one new instance from placement

Error message

Expected exactly one new instance from placement

What it means

Error "Expected exactly one new instance from placement" thrown in exo-explore/exo.

Source

Thrown at src/exo/api/main.py:502

                    min_nodes=min_nodes,
                ),
                node_memory=self.state.node_memory,
                node_network=self.state.node_network,
                node_backends=self.state.node_backends,
                topology=self.state.topology,
                current_instances=self.state.instances,
                download_status=self.state.downloads,
                node_rdma_ctl=self.state.node_rdma_ctl,
            )
        except ValueError as exc:
            raise HTTPException(status_code=400, detail=str(exc)) from exc

        current_ids = set(self.state.instances.keys())
        new_ids = [
            instance_id for instance_id in placements if instance_id not in current_ids
        ]
        if len(new_ids) != 1:
            raise HTTPException(
                status_code=500,
                detail="Expected exactly one new instance from placement",
            )

        return placements[new_ids[0]]

    async def get_placement_previews(
        self,
        model_id: ModelId,
        node_ids: Annotated[list[NodeId] | None, Query()] = None,
    ) -> PlacementPreviewResponse:
        seen: set[tuple[ModelId, Sharding, InstanceMeta, int]] = set()
        previews: list[PlacementPreview] = []
        required_nodes = set(node_ids) if node_ids else None

        if len(list(self.state.topology.list_nodes())) == 0:
            return PlacementPreviewResponse(previews=[])

View on GitHub (pinned to 21a54c5ea0)

When it happens

Trigger: Thrown at src/exo/api/main.py:502 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of exo-explore/exo@21a54c5ea0 (2026-08-26). Data as JSON: /api/errors/85c1775ccbe70bf9. Report an issue: GitHub.