launcher.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

import asyncio
import signal
import socket
from http import HTTPStatus
from typing import Any, Optional

import uvicorn
from fastapi import FastAPI, Request, Response

from vllm import envs
from vllm.engine.async_llm_engine import AsyncEngineDeadError
from vllm.engine.multiprocessing import MQEngineDeadError
from vllm.engine.protocol import EngineClient
from vllm.entrypoints.constants import (H11_MAX_HEADER_COUNT_DEFAULT,
                                        H11_MAX_INCOMPLETE_EVENT_SIZE_DEFAULT)
from vllm.entrypoints.ssl import SSLCertRefresher
from vllm.logger import init_logger
from vllm.utils import find_process_using_port
from vllm.v1.engine.exceptions import EngineDeadError, EngineGenerateError

logger = init_logger(__name__)


async def serve_http(app: FastAPI,
                     sock: Optional[socket.socket],
                     enable_ssl_refresh: bool = False,
                     **uvicorn_kwargs: Any):
    """
    Start a FastAPI app using Uvicorn, with support for custom Uvicorn config
    options.  Supports http header limits via h11_max_incomplete_event_size and
    h11_max_header_count.
    """
    logger.info("Available routes are:")
    for route in app.routes:
        methods = getattr(route, "methods", None)
        path = getattr(route, "path", None)

        if methods is None or path is None:
            continue

        logger.info("Route: %s, Methods: %s", path, ', '.join(methods))

    # Extract header limit options if present
    h11_max_incomplete_event_size = uvicorn_kwargs.pop(
        "h11_max_incomplete_event_size", None)
    h11_max_header_count = uvicorn_kwargs.pop("h11_max_header_count", None)

    # Set safe defaults if not provided
    if h11_max_incomplete_event_size is None:
        h11_max_incomplete_event_size = H11_MAX_INCOMPLETE_EVENT_SIZE_DEFAULT
    if h11_max_header_count is None:
        h11_max_header_count = H11_MAX_HEADER_COUNT_DEFAULT

    config = uvicorn.Config(app, **uvicorn_kwargs)
    # Set header limits
    config.h11_max_incomplete_event_size = h11_max_incomplete_event_size
    config.h11_max_header_count = h11_max_header_count
    config.load()
    server = uvicorn.Server(config)
    _add_shutdown_handlers(app, server)

    loop = asyncio.get_running_loop()

    watchdog_task = loop.create_task(
        watchdog_loop(server, app.state.engine_client))
    server_task = loop.create_task(
        server.serve(sockets=[sock] if sock else None))

    ssl_cert_refresher = None if not enable_ssl_refresh else SSLCertRefresher(
        ssl_context=config.ssl,
        key_path=config.ssl_keyfile,
        cert_path=config.ssl_certfile,
        ca_path=config.ssl_ca_certs)

    def signal_handler() -> None:
        # prevents the uvicorn signal handler to exit early
        server_task.cancel()
        watchdog_task.cancel()
        if ssl_cert_refresher:
            ssl_cert_refresher.stop()

    async def dummy_shutdown() -> None:
        pass

    loop.add_signal_handler(signal.SIGINT, signal_handler)
    loop.add_signal_handler(signal.SIGTERM, signal_handler)

    try:
        await server_task
        return dummy_shutdown()
    except asyncio.CancelledError:
        port = uvicorn_kwargs["port"]
        process = find_process_using_port(port)
        if process is not None:
            logger.debug(
                "port %s is used by process %s launched with command:\n%s",
                port, process, " ".join(process.cmdline()))
        logger.info("Shutting down FastAPI HTTP server.")
        return server.shutdown()
    finally:
        watchdog_task.cancel()


async def watchdog_loop(server: uvicorn.Server, engine: EngineClient):
    """
    # Watchdog task that runs in the background, checking
    # for error state in the engine. Needed to trigger shutdown
    # if an exception arises is StreamingResponse() generator.
    """
    VLLM_WATCHDOG_TIME_S = 5.0
    while True:
        await asyncio.sleep(VLLM_WATCHDOG_TIME_S)
        terminate_if_errored(server, engine)


def terminate_if_errored(server: uvicorn.Server, engine: EngineClient):
    """
    See discussions here on shutting down a uvicorn server
    https://github.com/encode/uvicorn/discussions/1103
    In this case we cannot await the server shutdown here
    because handler must first return to close the connection
    for this request.
    """
    engine_errored = engine.errored and not engine.is_running
    if not envs.VLLM_KEEP_ALIVE_ON_ENGINE_DEATH and engine_errored:
        server.should_exit = True


def _add_shutdown_handlers(app: FastAPI, server: uvicorn.Server) -> None:
    """
    VLLM V1 AsyncLLM catches exceptions and returns
    only two types: EngineGenerateError and EngineDeadError.
    
    EngineGenerateError is raised by the per request generate()
    method. This error could be request specific (and therefore
    recoverable - e.g. if there is an error in input processing).
    
    EngineDeadError is raised by the background output_handler
    method. This error is global and therefore not recoverable.
    
    We register these @app.exception_handlers to return nice
    responses to the end user if they occur and shut down if needed.
    See https://fastapi.tiangolo.com/tutorial/handling-errors/
    for more details on how exception handlers work.

    If an exception is encountered in a StreamingResponse
    generator, the exception is not raised, since we already sent
    a 200 status. Rather, we send an error message as the next chunk.
    Since the exception is not raised, this means that the server
    will not automatically shut down. Instead, we use the watchdog
    background task for check for errored state.
    """

    @app.exception_handler(RuntimeError)
    @app.exception_handler(AsyncEngineDeadError)
    @app.exception_handler(MQEngineDeadError)
    @app.exception_handler(EngineDeadError)
    @app.exception_handler(EngineGenerateError)
    async def runtime_exception_handler(request: Request, __):
        terminate_if_errored(
            server=server,
            engine=request.app.state.engine_client,
        )

        return Response(status_code=HTTPStatus.INTERNAL_SERVER_ERROR)