docker-compose/ai/simple_vllm_server.py

#!/usr/bin/env python3
"""
Simple vLLM server using AsyncLLMEngine directly
Bypasses the multiprocessing issues we hit with the default vLLM API server
OpenAI-compatible endpoints: /v1/models and /v1/completions
"""

import asyncio
import json
import logging
import os
from typing import AsyncIterator, Dict, List, Optional

from fastapi import FastAPI, Request
from fastapi.responses import JSONResponse, StreamingResponse
from pydantic import BaseModel, Field
from vllm import AsyncLLMEngine, AsyncEngineArgs, SamplingParams
from vllm.utils import random_uuid

# Configure logging
logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s - %(name)s - %(levelname)s - %(message)s'
)
logger = logging.getLogger(__name__)

# FastAPI app
app = FastAPI(title="Simple vLLM Server", version="1.0.0")

# Global engine instance
engine: Optional[AsyncLLMEngine] = None
model_name: str = "Qwen/Qwen2.5-7B-Instruct"

# Request/Response models
class CompletionRequest(BaseModel):
    """OpenAI-compatible completion request"""
    model: str = Field(default="qwen-2.5-7b")
    prompt: str | List[str] = Field(..., description="Text prompt(s)")
    max_tokens: int = Field(default=512, ge=1, le=4096)
    temperature: float = Field(default=0.7, ge=0.0, le=2.0)
    top_p: float = Field(default=1.0, ge=0.0, le=1.0)
    n: int = Field(default=1, ge=1, le=10)
    stream: bool = Field(default=False)
    stop: Optional[str | List[str]] = None
    presence_penalty: float = Field(default=0.0, ge=-2.0, le=2.0)
    frequency_penalty: float = Field(default=0.0, ge=-2.0, le=2.0)

class ChatMessage(BaseModel):
    """Chat message format"""
    role: str = Field(..., description="Role: system, user, or assistant")
    content: str = Field(..., description="Message content")

class ChatCompletionRequest(BaseModel):
    """OpenAI-compatible chat completion request"""
    model: str = Field(default="qwen-2.5-7b")
    messages: List[ChatMessage] = Field(..., description="Chat messages")
    max_tokens: int = Field(default=512, ge=1, le=4096)
    temperature: float = Field(default=0.7, ge=0.0, le=2.0)
    top_p: float = Field(default=1.0, ge=0.0, le=1.0)
    n: int = Field(default=1, ge=1, le=10)
    stream: bool = Field(default=False)
    stop: Optional[str | List[str]] = None

@app.on_event("startup")
async def startup_event():
    """Initialize vLLM engine on startup"""
    global engine, model_name

    logger.info(f"Initializing vLLM AsyncLLMEngine with model: {model_name}")

    # Configure engine
    engine_args = AsyncEngineArgs(
        model=model_name,
        tensor_parallel_size=1,  # Single GPU
        gpu_memory_utilization=0.85,  # Use 85% of GPU memory
        max_model_len=4096,  # Context length
        dtype="auto",  # Auto-detect dtype
        download_dir="/workspace/huggingface_cache",  # Large disk
        trust_remote_code=True,  # Some models require this
        enforce_eager=False,  # Use CUDA graphs for better performance
    )

    # Create async engine
    engine = AsyncLLMEngine.from_engine_args(engine_args)

    logger.info("vLLM AsyncLLMEngine initialized successfully")

@app.get("/")
async def root():
    """Health check endpoint"""
    return {"status": "ok", "model": model_name}

@app.get("/health")
async def health():
    """Detailed health check"""
    return {
        "status": "healthy" if engine else "initializing",
        "model": model_name,
        "ready": engine is not None
    }

@app.get("/v1/models")
async def list_models():
    """OpenAI-compatible models endpoint"""
    return {
        "object": "list",
        "data": [
            {
                "id": "qwen-2.5-7b",
                "object": "model",
                "created": 1234567890,
                "owned_by": "pivoine-gpu",
                "permission": [],
                "root": model_name,
                "parent": None,
            }
        ]
    }

def messages_to_prompt(messages: List[ChatMessage]) -> str:
    """Convert chat messages to a single prompt string"""
    # Qwen 2.5 chat template format
    prompt_parts = []

    for msg in messages:
        role = msg.role
        content = msg.content

        if role == "system":
            prompt_parts.append(f"<|im_start|>system\n{content}<|im_end|>")
        elif role == "user":
            prompt_parts.append(f"<|im_start|>user\n{content}<|im_end|>")
        elif role == "assistant":
            prompt_parts.append(f"<|im_start|>assistant\n{content}<|im_end|>")

    # Add final assistant prompt
    prompt_parts.append("<|im_start|>assistant\n")

    return "\n".join(prompt_parts)

@app.post("/v1/completions")
async def create_completion(request: CompletionRequest):
    """OpenAI-compatible completion endpoint"""
    if not engine:
        return JSONResponse(
            status_code=503,
            content={"error": "Engine not initialized"}
        )

    # Handle both single prompt and batch prompts
    prompts = [request.prompt] if isinstance(request.prompt, str) else request.prompt

    # Configure sampling parameters
    sampling_params = SamplingParams(
        temperature=request.temperature,
        top_p=request.top_p,
        max_tokens=request.max_tokens,
        n=request.n,
        stop=request.stop if request.stop else [],
        presence_penalty=request.presence_penalty,
        frequency_penalty=request.frequency_penalty,
    )

    # Generate completions
    results = []
    for prompt in prompts:
        request_id = random_uuid()

        if request.stream:
            # Streaming response
            async def generate_stream():
                async for output in engine.generate(prompt, sampling_params, request_id):
                    chunk = {
                        "id": request_id,
                        "object": "text_completion",
                        "created": 1234567890,
                        "model": request.model,
                        "choices": [
                            {
                                "text": output.outputs[0].text,
                                "index": 0,
                                "logprobs": None,
                                "finish_reason": output.outputs[0].finish_reason,
                            }
                        ]
                    }
                    yield f"data: {json.dumps(chunk)}\n\n"
                yield "data: [DONE]\n\n"

            return StreamingResponse(generate_stream(), media_type="text/event-stream")
        else:
            # Non-streaming response
            async for output in engine.generate(prompt, sampling_params, request_id):
                final_output = output

            results.append({
                "text": final_output.outputs[0].text,
                "index": len(results),
                "logprobs": None,
                "finish_reason": final_output.outputs[0].finish_reason,
            })

    return {
        "id": random_uuid(),
        "object": "text_completion",
        "created": 1234567890,
        "model": request.model,
        "choices": results,
        "usage": {
            "prompt_tokens": 0,  # vLLM doesn't expose this easily
            "completion_tokens": 0,
            "total_tokens": 0,
        }
    }

@app.post("/v1/chat/completions")
async def create_chat_completion(request: ChatCompletionRequest):
    """OpenAI-compatible chat completion endpoint"""
    if not engine:
        return JSONResponse(
            status_code=503,
            content={"error": "Engine not initialized"}
        )

    # Convert messages to prompt
    prompt = messages_to_prompt(request.messages)

    # Configure sampling parameters
    sampling_params = SamplingParams(
        temperature=request.temperature,
        top_p=request.top_p,
        max_tokens=request.max_tokens,
        n=request.n,
        stop=request.stop if request.stop else ["<|im_end|>"],
    )

    request_id = random_uuid()

    if request.stream:
        # Streaming response
        async def generate_stream():
            async for output in engine.generate(prompt, sampling_params, request_id):
                chunk = {
                    "id": request_id,
                    "object": "chat.completion.chunk",
                    "created": 1234567890,
                    "model": request.model,
                    "choices": [
                        {
                            "index": 0,
                            "delta": {"content": output.outputs[0].text},
                            "finish_reason": output.outputs[0].finish_reason,
                        }
                    ]
                }
                yield f"data: {json.dumps(chunk)}\n\n"
            yield "data: [DONE]\n\n"

        return StreamingResponse(generate_stream(), media_type="text/event-stream")
    else:
        # Non-streaming response
        async for output in engine.generate(prompt, sampling_params, request_id):
            final_output = output

        return {
            "id": request_id,
            "object": "chat.completion",
            "created": 1234567890,
            "model": request.model,
            "choices": [
                {
                    "index": 0,
                    "message": {
                        "role": "assistant",
                        "content": final_output.outputs[0].text,
                    },
                    "finish_reason": final_output.outputs[0].finish_reason,
                }
            ],
            "usage": {
                "prompt_tokens": 0,
                "completion_tokens": 0,
                "total_tokens": 0,
            }
        }

if __name__ == "__main__":
    import uvicorn

    # Get configuration from environment
    host = os.getenv("VLLM_HOST", "0.0.0.0")
    port = int(os.getenv("VLLM_PORT", "8000"))

    logger.info(f"Starting vLLM server on {host}:{port}")

    uvicorn.run(
        app,
        host=host,
        port=port,
        log_level="info",
        access_log=True,
    )