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LangServe

LangServe is a popular runtime to execute LangChain applications.
LangStream natively integrates with LangServe and allows you to invoke services exposed by LangServe applications.
Use the built-in langserve-invoke agent to implement this integration.
This example invokes a LangServe application that exposes a service at http://localhost:8000/chain/stream.
topics:
- name: "input-topic"
creation-mode: create-if-not-exists
- name: "output-topic"
creation-mode: create-if-not-exists
- name: "streaming-answers-topic"
creation-mode: create-if-not-exists
pipeline:
- type: "langserve-invoke"
input: input-topic
output: output-topic
id: step1
configuration:
output-field: value.answer
stream-to-topic: streaming-answers-topic
stream-response-field: value
min-chunks-per-message: 10
debug: false
method: POST
allow-redirects: true
handle-cookies: false
url: "http://host.docker.internal:8000/chain/stream"
fields:
- name: topic
expression: "value"
When you run the LangStream application in docker the URL is http://host.docker.internal:8000/chain/stream due to how docker desktop works.
To allow your LangStream application to be accessible from a UI, you have to configure a gateway:
gateways:
- id: chat
type: chat
chat-options:
answers-topic: streaming-answers-topic
questions-topic: input-topic
headers:
- value-from-parameters: session-id

Starting the LangServe application locally

This is the sample code of the LangServe application:
from fastapi import FastAPI
from langchain.prompts import ChatPromptTemplate
from langchain.chat_models import ChatOpenAI
from langserve import add_routes
app = FastAPI(
title="LangChain Server",
version="1.0",
description="A simple api server using Langchain's Runnable interfaces",
)
model = ChatOpenAI()
prompt = ChatPromptTemplate.from_template("tell me a joke about {topic}")
add_routes(
app,
prompt | model,
path="/chain",
)
if __name__ == "__main__":
import uvicorn
uvicorn.run(app, host="localhost", port=8000)
Start the LangServe application with the following command:
export OPENAI_API_KEY=...
pip install fastapi langserve langchain openai sse_starlette uvicorn
python example.py

Starting the LangStream application locally

To run the LangStream application on docker locally:
langstream docker run -app /path/to/applicationn
The LangStream UI will be running at http://localhost:8092/
Last modified 3mo ago