[BugFix]: Properly set engine_id when using multi connector (#19487)

Signed-off-by: Nick Hill <nhill@redhat.com>
Co-authored-by: leiyiming <leiyiming@kingsoft.com>
Co-authored-by: Nick Hill <nhill@redhat.com>

tests/v1/kv_connector/unit/test_multi_connector.py

@@ -76,6 +76,9 @@ class TestSharedStorageConnector(SharedStorageConnector):
         return attr
 
 
+# This relies on "fork" multiprocessing method being used.
+# It's the default but vLLM may fall back to spawn if for example CUDA
+# is already initialized.
 KVConnectorFactory.register_connector("TestSharedStorageConnector",
                                       TestSharedStorageConnector.__module__,
                                       TestSharedStorageConnector.__name__)

tests/v1/kv_connector/unit/test_nixl_connector.py

@@ -166,8 +166,8 @@ class FakeNixlConnectorWorker(NixlConnectorWorker):
         super().__init__(*args, **kwargs)
         self._hand_shake_latency = hand_shake_latency
 
-    def _nixl_handshake(self, host: str, port: int,
-                        remote_tp_size: int) -> dict[int, str]:
+    def _nixl_handshake(self, host: str, port: int, remote_tp_size: int,
+                        expected_engine_id: str) -> dict[int, str]:
         # Mimic slow _nixl_handshake, as well as bypass zmq communication.
         time.sleep(self._hand_shake_latency)
         # These should've been done in register_kv_caches(), called by
@@ -177,6 +177,8 @@ class FakeNixlConnectorWorker(NixlConnectorWorker):
         self.num_blocks = 1
         self.dst_num_blocks[self.engine_id] = self.num_blocks
 
+        assert expected_engine_id == self.REMOTE_ENGINE_ID
+
         remote_agent_name = self.add_remote_agent(
             NixlAgentMetadata(
                 engine_id=self.REMOTE_ENGINE_ID,

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

@@ -47,7 +47,10 @@ class MultiConnector(KVConnectorBase_V1):
         assert ktcs is not None
         for ktc in ktcs:
             temp_config = copy.copy(vllm_config)
-            temp_config.kv_transfer_config = KVTransferConfig(**ktc)
+            engine_id = ktc.get("engine_id",
+                                vllm_config.kv_transfer_config.engine_id)
+            temp_config.kv_transfer_config = KVTransferConfig(
+                **ktc, engine_id=engine_id)
             self._connectors.append(
                 KVConnectorFactory.create_connector_v1(temp_config, role))
 
@@ -187,7 +190,7 @@ class MultiConnector(KVConnectorBase_V1):
                 async_saves += 1
             if txfer_params is not None:
                 if kv_txfer_params is not None:
-                    #TODO we can probably change this to merge the dicts here,
+                    # TODO we can probably change this to merge the dicts here,
                     # checking for key clashes.
                     raise RuntimeError(
                         "Only one connector can produce KV transfer params")

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

@@ -488,8 +488,13 @@ class NixlConnectorWorker:
                         "Connection listener got unexpected message %s", msg)
                 sock.send_multipart((identity, b"", encoded_data))
 
-    def _nixl_handshake(self, host: str, port: int,
-                        remote_tp_size: int) -> dict[int, str]:
+    def _nixl_handshake(
+        self,
+        host: str,
+        port: int,
+        remote_tp_size: int,
+        expected_engine_id: str,
+    ) -> dict[int, str]:
         """Do a NIXL handshake with a remote instance."""
 
         start_time = time.perf_counter()
@@ -498,26 +503,6 @@ class NixlConnectorWorker:
         # a hack to keep us moving. We will switch when moving to etcd
         # or where we have a single ZMQ socket in the scheduler.
 
-        def handshake(path: str, rank: int) -> str:
-            # Send query for the request.
-            with zmq_ctx(zmq.REQ, path) as sock:
-                sock.send(GET_META_MSG)
-                metadata_bytes = sock.recv()
-                decoder = msgspec.msgpack.Decoder(NixlAgentMetadata)
-                metadata = decoder.decode(metadata_bytes)
-                got_metadata_time = time.perf_counter()
-
-                # Register Remote agent.
-                remote_agent_name = self.add_remote_agent(
-                    metadata, rank, remote_tp_size)
-                setup_agent_time = time.perf_counter()
-
-                logger.debug("NIXL handshake: get metadata took: %s",
-                             got_metadata_time - start_time)
-                logger.debug("NIXL handshake: add agent took: %s",
-                             setup_agent_time - got_metadata_time)
-                return remote_agent_name
-
         # Handshake only with the remote TP rank that current local rank will
         # pull from. With homogeneous TP it happens to be the same rank_i.
         tp_ratio = self._tp_size[self.engine_id] // remote_tp_size
@@ -525,8 +510,32 @@ class NixlConnectorWorker:
         path = make_zmq_path("tcp", host, port + p_remote_rank)
         logger.debug("Querying metadata on path: %s at remote rank %s", path,
                      p_remote_rank)
+
+        # Send query for the request.
+        with zmq_ctx(zmq.REQ, path) as sock:
+            sock.send(GET_META_MSG)
+            metadata_bytes = sock.recv()
+            decoder = msgspec.msgpack.Decoder(NixlAgentMetadata)
+            metadata = decoder.decode(metadata_bytes)
+            got_metadata_time = time.perf_counter()
+            logger.debug("NIXL handshake: get metadata took: %s",
+                         got_metadata_time - start_time)
+
+            # Ensure engine id matches.
+            if metadata.engine_id != expected_engine_id:
+                raise RuntimeError(f"Remote NIXL agent engine ID mismatch. "
+                                   f"Expected {expected_engine_id},"
+                                   f"received {metadata.engine_id}.")
+
+            # Register Remote agent.
+            remote_agent_name = self.add_remote_agent(metadata, p_remote_rank,
+                                                      remote_tp_size)
+            setup_agent_time = time.perf_counter()
+            logger.debug("NIXL handshake: add agent took: %s",
+                         setup_agent_time - got_metadata_time)
+
         # Remote rank -> agent name.
-        return {p_remote_rank: handshake(path, p_remote_rank)}
+        return {p_remote_rank: remote_agent_name}
 
     def _background_nixl_handshake(self, req_id: str,
                                    remote_engine_id: EngineId, meta: ReqMeta):
@@ -535,7 +544,7 @@ class NixlConnectorWorker:
         if fut is None:
             fut = self._handshake_initiation_executor.submit(
                 self._nixl_handshake, meta.remote_host, meta.remote_port,
-                meta.tp_size)
+                meta.tp_size, remote_engine_id)
             self._handshake_futures[remote_engine_id] = fut
 
             def done_callback(f: Future[dict[int, str]], eid=remote_engine_id):
@@ -738,10 +747,10 @@ class NixlConnectorWorker:
         if remote_tp_rank in self._remote_agents.get(engine_id, {}):
             return self._remote_agents[engine_id][remote_tp_rank]
 
-        if engine_id in self._tp_size:
-            assert self._tp_size[engine_id] == remote_tp_size
-        else:
+        if engine_id not in self._tp_size:
             self._tp_size[engine_id] = remote_tp_size
+        else:
+            assert self._tp_size[engine_id] == remote_tp_size
         # We may eventually enable this after asserting equality in cache
         # layout and close outputs.
         assert nixl_agent_meta.attn_backend_name == self.backend_name