[Misc] Introduce ec_both role EC (encoder cache) connector (#34182)

Signed-off-by: Qi Wang <qiwa@nvidia.com>

vllm/config/ec_transfer.py

@@ -7,8 +7,8 @@ from typing import Any, Literal, get_args
 
 from vllm.config.utils import config
 
-ECProducer = Literal["ec_producer"]
-ECConsumer = Literal["ec_consumer"]
+ECProducer = Literal["ec_producer", "ec_both"]
+ECConsumer = Literal["ec_consumer", "ec_both"]
 ECRole = Literal[ECProducer, ECConsumer]
 
 
@@ -33,7 +33,7 @@ class ECTransferConfig:
 
     ec_role: ECRole | None = None
     """Whether this vLLM instance produces, consumes EC cache, or both. Choices
-    are 'ec_producer', 'ec_consumer'."""
+    are 'ec_producer', 'ec_consumer', 'ec_both'."""
 
     ec_rank: int | None = None
     """The rank of this vLLM instance in the EC cache transfer. Typical value:

vllm/distributed/ec_transfer/ec_connector/base.py

@@ -63,6 +63,7 @@ class ECConnectorBase(ABC):
         self._role = role
         if vllm_config.ec_transfer_config is not None:
             self._is_producer = vllm_config.ec_transfer_config.is_ec_producer
+            self._is_consumer = vllm_config.ec_transfer_config.is_ec_consumer
         else:
             raise ValueError("ec_transfer_config must be set for ECConnectorBase")
 
@@ -74,6 +75,10 @@ class ECConnectorBase(ABC):
     def is_producer(self) -> bool:
         return self._is_producer
 
+    @property
+    def is_consumer(self) -> bool:
+        return self._is_consumer
+
     # ==============================
     # Worker-side methods
     # ==============================

vllm/v1/worker/ec_connector_model_runner_mixin.py

@@ -72,7 +72,8 @@ class ECConnectorModelRunnerMixin:
         assert scheduler_output.ec_connector_metadata is not None
         ec_connector.bind_connector_metadata(scheduler_output.ec_connector_metadata)
 
-        if not ec_connector.is_producer:
+        # Load caches for consumer or both roles
+        if ec_connector.is_consumer:
             ec_connector.start_load_caches(encoder_cache, **kwargs)
 
         try: