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Haystack

Haystack is an end-to-end LLM framework that allows you to build applications powered by LLMs, Transformer models, vector search and more. Whether you want to perform retrieval-augmented generation (RAG), document search, question answering or answer generation, Haystack can orchestrate state-of-the-art embedding models and LLMs into pipelines to build end-to-end NLP applications and solve your use case.

It allows you to deploy a large language model (LLM) server with vLLM as the backend, which exposes OpenAI-compatible endpoints.

Prerequisites

  • Setup vLLM and Haystack environment
pip install vllm haystack-ai

Deploy

  • Start the vLLM server with the supported chat completion model, e.g.
vllm serve mistralai/Mistral-7B-Instruct-v0.1
  • Use the OpenAIGenerator and OpenAIChatGenerator components in Haystack to query the vLLM server.
Code 
from haystack.components.generators.chat import OpenAIChatGenerator
from haystack.dataclasses import ChatMessage
from haystack.utils import Secret

generator = OpenAIChatGenerator(
    # for compatibility with the OpenAI API, a placeholder api_key is needed
    api_key=Secret.from_token("VLLM-PLACEHOLDER-API-KEY"),
    model="mistralai/Mistral-7B-Instruct-v0.1",
    api_base_url="http://{your-vLLM-host-ip}:{your-vLLM-host-port}/v1",
    generation_kwargs = {"max_tokens": 512}
)

response = generator.run(
  messages=[ChatMessage.from_user("Hi. Can you help me plan my next trip to Italy?")]
)

print("-"*30)
print(response)
print("-"*30)

------------------------------
{'replies': [ChatMessage(_role=<ChatRole.ASSISTANT: 'assistant'>, _content=[TextContent(text=' Of course! Where in Italy would you like to go and what type of trip are you looking to plan?')], _name=None, _meta={'model': 'mistralai/Mistral-7B-Instruct-v0.1', 'index': 0, 'finish_reason': 'stop', 'usage': {'completion_tokens': 23, 'prompt_tokens': 21, 'total_tokens': 44, 'completion_tokens_details': None, 'prompt_tokens_details': None}})]}
------------------------------

For details, see the tutorial Using vLLM in Haystack.