[Bug]: Request Cancelation w/ Scheduler Steps Set Causes K8s Pod Restart

[sam-h-bean]

Your current environment

I am running K8s vLLM OpenAI compatible server on version 0.5.5. The client was a locust load test.

🐛 Describe the bug

INFO:     10.65.62.6:37396 - "POST /v1/chat/completions HTTP/1.1" 500 Internal Server Error
ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "/usr/local/lib/python3.10/dist-packages/uvicorn/protocols/http/httptools_impl.py", line 401, in run_asgi
    result = await app(  # type: ignore[func-returns-value]
  File "/usr/local/lib/python3.10/dist-packages/uvicorn/middleware/proxy_headers.py", line 70, in __call__
    return await self.app(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/fastapi/applications.py", line 1054, in __call__
    await super().__call__(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/applications.py", line 123, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/middleware/errors.py", line 186, in __call__
    raise exc
  File "/usr/local/lib/python3.10/dist-packages/starlette/middleware/errors.py", line 164, in __call__
    await self.app(scope, receive, _send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/middleware/cors.py", line 85, in __call__
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/middleware/exceptions.py", line 65, in __call__
    await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/_exception_handler.py", line 64, in wrapped_app
    raise exc
  File "/usr/local/lib/python3.10/dist-packages/starlette/_exception_handler.py", line 53, in wrapped_app
    await app(scope, receive, sender)
  File "/usr/local/lib/python3.10/dist-packages/starlette/routing.py", line 754, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/routing.py", line 774, in app
    await route.handle(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/routing.py", line 295, in handle
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/routing.py", line 77, in app
    await wrap_app_handling_exceptions(app, request)(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/_exception_handler.py", line 64, in wrapped_app
    raise exc
  File "/usr/local/lib/python3.10/dist-packages/starlette/_exception_handler.py", line 53, in wrapped_app
    await app(scope, receive, sender)
  File "/usr/local/lib/python3.10/dist-packages/starlette/routing.py", line 74, in app
    response = await f(request)
  File "/usr/local/lib/python3.10/dist-packages/fastapi/routing.py", line 278, in app
    raw_response = await run_endpoint_function(
  File "/usr/local/lib/python3.10/dist-packages/fastapi/routing.py", line 191, in run_endpoint_function
    return await dependant.call(**values)
  File "/usr/local/lib/python3.10/dist-packages/vllm/entrypoints/openai/api_server.py", line 271, in create_chat_completion
    generator = await openai_serving_chat.create_chat_completion(
  File "/usr/local/lib/python3.10/dist-packages/vllm/entrypoints/openai/serving_chat.py", line 188, in create_chat_completion
    return await self.chat_completion_full_generator(
  File "/usr/local/lib/python3.10/dist-packages/vllm/entrypoints/openai/serving_chat.py", line 438, in chat_completion_full_generator
    async for res in result_generator:
  File "/usr/local/lib/python3.10/dist-packages/vllm/utils.py", line 430, in iterate_with_cancellation
    item = await awaits[0]
  File "/usr/local/lib/python3.10/dist-packages/vllm/entrypoints/openai/rpc/client.py", line 416, in generate
    raise request_output
AssertionError: expected running sequences
CRITICAL 08-26 11:25:19 launcher.py:98] AsyncLLMEngine is already dead, terminating server process
INFO:     10.65.62.6:37412 - "POST /v1/chat/completions HTTP/1.1" 500 Internal Server Error
CRITICAL 08-26 11:25:19 launcher.py:98] AsyncLLMEngine is already dead, terminating server process
INFO:     10.65.62.6:37424 - "POST /v1/chat/completions HTTP/1.1" 500 Internal Server Error
INFO:     Shutting down
INFO:     Waiting for application shutdown.
INFO:     Application shutdown complete.
INFO:     Finished server process [1]

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[comaniac]

The assertion is in https://github.com/vllm-project/vllm/blob/main/vllm/engine/output_processor/multi_step.py#L73. I've added this to the multi-step issue tracker.

Also cc @SolitaryThinker @alexm-neuralmagic

[robertgshaw2-neuralmagic]

Fixed by: #8059