[Misc] KV cache transfer connector registry (#11481)

Signed-off-by: KuntaiDu <kuntai@uchicago.edu>

vllm/config.py

@@ -2559,14 +2559,6 @@ class KVTransferConfig(BaseModel):
         return KVTransferConfig.model_validate_json(cli_value)
 
     def model_post_init(self, __context: Any) -> None:
-        supported_kv_connector = ["PyNcclConnector", "MooncakeConnector"]
-        if all([
-                self.kv_connector is not None, self.kv_connector
-                not in supported_kv_connector
-        ]):
-            raise ValueError(f"Unsupported kv_connector: {self.kv_connector}. "
-                             f"Supported connectors are "
-                             f"{supported_kv_connector}.")
 
         if self.kv_role is not None and self.kv_role not in [
                 "kv_producer", "kv_consumer", "kv_both"

vllm/distributed/kv_transfer/kv_connector/factory.py

-from typing import TYPE_CHECKING
+import importlib
+from typing import TYPE_CHECKING, Callable, Dict, Type
 
 from .base import KVConnectorBase
 
@@ -7,14 +8,41 @@ if TYPE_CHECKING:
 
 
 class KVConnectorFactory:
+    _registry: Dict[str, Callable[[], Type[KVConnectorBase]]] = {}
 
-    @staticmethod
-    def create_connector(rank: int, local_rank: int,
+    @classmethod
+    def register_connector(cls, name: str, module_path: str,
+                           class_name: str) -> None:
+        """Register a connector with a lazy-loading module and class name."""
+        if name in cls._registry:
+            raise ValueError(f"Connector '{name}' is already registered.")
+
+        def loader() -> Type[KVConnectorBase]:
+            module = importlib.import_module(module_path)
+            return getattr(module, class_name)
+
+        cls._registry[name] = loader
+
+    @classmethod
+    def create_connector(cls, rank: int, local_rank: int,
                          config: "VllmConfig") -> KVConnectorBase:
-        supported_kv_connector = ["PyNcclConnector", "MooncakeConnector"]
-        if config.kv_transfer_config.kv_connector in supported_kv_connector:
-            from .simple_connector import SimpleConnector
-            return SimpleConnector(rank, local_rank, config)
-        else:
-            raise ValueError(f"Unsupported connector type: "
-                             f"{config.kv_connector}")
+        connector_name = config.kv_transfer_config.kv_connector
+        if connector_name not in cls._registry:
+            raise ValueError(f"Unsupported connector type: {connector_name}")
+
+        connector_cls = cls._registry[connector_name]()
+        return connector_cls(rank, local_rank, config)
+
+
+# Register various connectors here.
+# The registration should not be done in each individual file, as we want to
+# only load the files corresponding to the current connector.
+KVConnectorFactory.register_connector(
+    "PyNcclConnector",
+    "vllm.distributed.kv_transfer.kv_connector.simple_connector",
+    "SimpleConnector")
+
+KVConnectorFactory.register_connector(
+    "MooncakeConnector",
+    "vllm.distributed.kv_transfer.kv_connector.simple_connector",
+    "SimpleConnector")