[TPU] Support tensor parallelism in async llm engine (#6891)

Dockerfile.tpu

@@ -12,6 +12,9 @@ RUN pip install "numpy<2"
 RUN pip install torch_xla[tpu] -f https://storage.googleapis.com/libtpu-releases/index.html
 RUN pip install torch_xla[pallas] -f https://storage.googleapis.com/jax-releases/jax_nightly_releases.html -f https://storage.googleapis.com/jax-releases/jaxlib_nightly_releases.html
 
+# Fix FastAPI dependence
+RUN pip install "starlette<0.38.0"
+
 # Build vLLM.
 COPY . /workspace/vllm
 ENV VLLM_TARGET_DEVICE="tpu"

vllm/engine/async_llm_engine.py

@@ -407,6 +407,12 @@ class AsyncLLMEngine:
             from vllm.executor.neuron_executor import NeuronExecutorAsync
             executor_class = NeuronExecutorAsync
         elif engine_config.device_config.device_type == "tpu":
+            if distributed_executor_backend == "ray":
+                initialize_ray_cluster(engine_config.parallel_config)
+                from vllm.executor.ray_tpu_executor import RayTPUExecutorAsync
+                executor_class = RayTPUExecutorAsync
+            else:
+                assert distributed_executor_backend is None
                 from vllm.executor.tpu_executor import TPUExecutorAsync
                 executor_class = TPUExecutorAsync
         elif engine_config.device_config.device_type == "cpu":