[Bugfix] Set `KVTransferConfig.engine_id` in post_init (#18576)

Signed-off-by: Linkun Chen <github@lkchen.net>

tests/v1/kv_connector/unit/test_multi_connector.py

@@ -239,3 +239,11 @@ def get_connector_events() -> dict[str, list[str]]:
             print(f"[ERROR] Could not read connector events for {name}: {e}")
 
     return connector_events
+
+
+def test_engine_id_conflict():
+    configs = [KVTransferConfig() for _ in range(2)]
+    ids = [config.engine_id for config in configs]
+    assert ids[0] != ids[1], (
+        "Engine IDs should be different for different configs. "
+        f"Got {ids}")

vllm/config.py

@@ -3495,7 +3495,7 @@ class KVTransferConfig:
     """The KV connector for vLLM to transmit KV caches between vLLM instances.
     """
 
-    engine_id: str = str(uuid.uuid4())
+    engine_id: Optional[str] = None
     """The engine id for KV transfers."""
 
     kv_buffer_device: Optional[str] = "cuda"
@@ -3552,6 +3552,9 @@ class KVTransferConfig:
         return hash_str
 
     def __post_init__(self) -> None:
+        if self.engine_id is None:
+            self.engine_id = str(uuid.uuid4())
+
         if self.kv_role is not None and self.kv_role not in get_args(KVRole):
             raise ValueError(f"Unsupported kv_role: {self.kv_role}. "
                              f"Supported roles are {get_args(KVRole)}")

vllm/distributed/kv_transfer/kv_connector/v1/nixl_connector.py

@@ -537,6 +537,7 @@ class NixlConnectorWorker:
 
     def add_remote_agent(self, nixl_agent_meta: NixlAgentMetadata):
         engine_id = nixl_agent_meta.engine_id
+        assert engine_id != self.engine_id, "Conflict engine id found!"
         if engine_id in self._remote_agents:
             return