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docs/source/serving/distributed_serving.rst

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+.. _distributed_serving:
+
+Distributed Inference and Serving
+=================================
+
+vLLM supports distributed tensor-parallel inference and serving. Currently, we support `Megatron-LM's tensor parallel algorithm <https://arxiv.org/pdf/1909.08053.pdf>`_. We manage the distributed runtime with `Ray <https://github.com/ray-project/ray>`_. To run distributed inference, install Ray with:
+
+.. code-block:: console
+
+    $ pip install ray
+
+To run multi-GPU inference with the :code:`LLM` class, set the :code:`tensor_parallel_size` argument to the number of GPUs you want to use. For example, to run inference on 4 GPUs:
+
+.. code-block:: python
+
+    from vllm import LLM
+    llm = LLM("facebook/opt-13b", tensor_parallel_size=4)
+    output = llm.generate("San Franciso is a")
+
+To run multi-GPU serving, pass in the :code:`--tensor-parallel-size` argument when starting the server. For example, to run API server on 4 GPUs:
+
+.. code-block:: console
+
+    $ python -m vllm.entrypoints.api_server \
+    $     --model facebook/opt-13b \
+    $     --tensor-parallel-size 4
+
+To scale vLLM beyond a single machine, start a `Ray runtime <https://docs.ray.io/en/latest/ray-core/starting-ray.html>`_ via CLI before running vLLM:
+
+.. code-block:: console
+
+    $ # On head node
+    $ ray start --head
+
+    $ # On worker nodes
+    $ ray start --address=<ray-head-address>
+
+After that, you can run inference and serving on multiple machines by launching the vLLM process on the head node by setting :code:`tensor_parallel_size` to the number of GPUs to be the total number of GPUs across all machines.