[Feature] publisher default set zmq in kv_event config (#26915)

Signed-off-by: rongfu.leng <rongfu.leng@daocloud.io>
Co-authored-by: Cyrus Leung <tlleungac@connect.ust.hk>

Author: lengrongfu

vllm/config/kv_events.py

@@ -2,6 +2,9 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
 
+from typing import Literal
+
+from pydantic import Field
 from pydantic.dataclasses import dataclass
 
 from vllm.config.utils import config
@@ -17,7 +20,7 @@ class KVEventsConfig:
     Events can be published externally by zmq using the event publisher config.
     """
 
-    publisher: str = "null"
+    publisher: Literal["null", "zmq"] = Field(default=None)
     """The publisher to use for publishing kv events. Can be "null", "zmq".
     """
 
@@ -47,3 +50,7 @@ class KVEventsConfig:
     """The topic to use for the event publisher. Consumers can subscribe to
     this topic to receive events.
     """
+
+    def __post_init__(self):
+        if self.publisher is None:
+            self.publisher = "zmq" if self.enable_kv_cache_events else "null"

vllm/distributed/kv_events.py

@@ -353,12 +353,12 @@ def create(
         cls, config: KVEventsConfig | None, data_parallel_rank: int = 0
     ) -> EventPublisher:
         """Create publisher from a config mapping."""
-        if not config:
+        if config is None or config.publisher == "null":
             return NullEventPublisher()
 
         config_dict = asdict(config)
 
-        kind = config_dict.pop("publisher", "null")
+        kind = config_dict.pop("publisher")
         config_dict.pop("enable_kv_cache_events")
         try:
             constructor = cls._registry[kind]