Build RAG Chatbot with LangChain, OpenSearch, Google Vertex AI Gemini 2.0 Flash Thinking, and IBM slate-125m-english-rtrvr

Introduction to RAG

Retrieval-Augmented Generation (RAG) is a game-changer for GenAI applications, especially in conversational AI. It combines the power of pre-trained large language models (LLMs) like OpenAI’s GPT with external knowledge sources stored in vector databases such as Milvus and Zilliz Cloud, allowing for more accurate, contextually relevant, and up-to-date response generation. A RAG pipeline usually consists of four basic components: a vector database, an embedding model, an LLM, and a framework.

Key Components We'll Use for This RAG Chatbot

This tutorial shows you how to build a simple RAG chatbot in Python using the following components:

LangChain: An open-source framework that helps you orchestrate the interaction between LLMs, vector stores, embedding models, etc, making it easier to integrate a RAG pipeline.
OpenSearch: An open-source search and analytics suite derived from Elasticsearch. It offers robust full-text search and real-time analytics, with vector search available as an add-on for similarity-based queries, extending its capabilities to handle high-dimensional data. Since it is just a vector search add-on rather than a purpose-built vector database, it lacks scalability and availability and many other advanced features required by enterprise-level applications. Therefore, if you prefer a much more scalable solution or hate to manage your own infrastructure, we recommend using Zilliz Cloud, which is a fully managed vector database service built on the open-source Milvus and offers a free tier supporting up to 1 million vectors.)
Google Vertex AI Gemini 2.0 Flash Thinking: This advanced AI model is designed for rapid, high-quality cognitive analysis and decision-making. It leverages enhanced natural language understanding and generation, enabling seamless interactions. Ideal for real-time applications in customer service, content creation, and intelligent automation, it excels in scenarios that demand quick, insightful responses.
IBM slate-125m-english-rtrvr: This model is designed for fine-tuning English text retrieval tasks, leveraging a slim and efficient architecture. Its strength lies in fast processing and high accuracy, making it ideal for applications that require quick and relevant information retrieval from large text datasets. Use cases include document search engines, chatbots, and content recommendation systems.

By the end of this tutorial, you’ll have a functional chatbot capable of answering questions based on a custom knowledge base.

Note: Since we may use proprietary models in our tutorials, make sure you have the required API key beforehand.

Step 1: Install and Set Up LangChain

%pip install --quiet --upgrade langchain-text-splitters langchain-community langgraph

Step 2: Install and Set Up Google Vertex AI Gemini 2.0 Flash Thinking

pip install -qU "langchain[google-vertexai]"

# Ensure your VertexAI credentials are configured

from langchain.chat_models import init_chat_model

llm = init_chat_model("gemini-2.0-flash-thinking-exp-01-21", model_provider="google_vertexai")

Step 3: Install and Set Up IBM slate-125m-english-rtrvr

pip install -qU langchain-ibm

import getpass
import os

if not os.environ.get("WATSONX_APIKEY"):
  os.environ["WATSONX_APIKEY"] = getpass.getpass("Enter API key for IBM watsonx: ")

from langchain_ibm import WatsonxEmbeddings

embeddings = WatsonxEmbeddings(
    model_id="ibm/slate-125m-english-rtrvr",
    url="https://us-south.ml.cloud.ibm.com",
    project_id="<WATSONX PROJECT_ID>",
)

Step 4: Install and Set Up OpenSearch

pip install --upgrade --quiet  opensearch-py langchain-community

from langchain_community.vectorstores import OpenSearchVectorSearch
opensearch_vector_search = OpenSearchVectorSearch(
    "http://localhost:9200",
    "embeddings",
    embedding_function
)

Step 5: Build a RAG Chatbot

Now that you’ve set up all components, let’s start to build a simple chatbot. We’ll use the Milvus introduction doc as a private knowledge base. You can replace it with your own dataset to customize your RAG chatbot.

import bs4
from langchain import hub
from langchain_community.document_loaders import WebBaseLoader
from langchain_core.documents import Document
from langchain_text_splitters import RecursiveCharacterTextSplitter
from langgraph.graph import START, StateGraph
from typing_extensions import List, TypedDict

# Load and chunk contents of the blog
loader = WebBaseLoader(
    web_paths=("https://milvus.io/docs/overview.md",),
    bs_kwargs=dict(
        parse_only=bs4.SoupStrainer(
            class_=("doc-style doc-post-content")
        )
    ),
)

docs = loader.load()

text_splitter = RecursiveCharacterTextSplitter(chunk_size=1000, chunk_overlap=200)
all_splits = text_splitter.split_documents(docs)

# Index chunks
_ = vector_store.add_documents(documents=all_splits)

# Define prompt for question-answering
prompt = hub.pull("rlm/rag-prompt")


# Define state for application
class State(TypedDict):
    question: str
    context: List[Document]
    answer: str


# Define application steps
def retrieve(state: State):
    retrieved_docs = vector_store.similarity_search(state["question"])
    return {"context": retrieved_docs}


def generate(state: State):
    docs_content = "\n\n".join(doc.page_content for doc in state["context"])
    messages = prompt.invoke({"question": state["question"], "context": docs_content})
    response = llm.invoke(messages)
    return {"answer": response.content}


# Compile application and test
graph_builder = StateGraph(State).add_sequence([retrieve, generate])
graph_builder.add_edge(START, "retrieve")
graph = graph_builder.compile()

Test the Chatbot

Yeah! You've built your own chatbot. Let's ask the chatbot a question.

response = graph.invoke({"question": "What data types does Milvus support?"})
print(response["answer"])

Example Output

Milvus supports various data types including sparse vectors, binary vectors, JSON, and arrays. Additionally, it handles common numerical and character types, making it versatile for different data modeling needs. This allows users to manage unstructured or multi-modal data efficiently.

Optimization Tips

As you build your RAG system, optimization is key to ensuring peak performance and efficiency. While setting up the components is an essential first step, fine-tuning each one will help you create a solution that works even better and scales seamlessly. In this section, we’ll share some practical tips for optimizing all these components, giving you the edge to build smarter, faster, and more responsive RAG applications.

LangChain optimization tips

To optimize LangChain, focus on minimizing redundant operations in your workflow by structuring your chains and agents efficiently. Use caching to avoid repeated computations, speeding up your system, and experiment with modular design to ensure that components like models or databases can be easily swapped out. This will provide both flexibility and efficiency, allowing you to quickly scale your system without unnecessary delays or complications.

OpenSearch optimization tips

To optimize OpenSearch in a Retrieval-Augmented Generation (RAG) setup, fine-tune indexing by enabling efficient mappings and reducing unnecessary stored fields. Use HNSW for vector search to speed up similarity queries while balancing recall and latency with appropriate ef_search and ef_construction values. Leverage shard and replica settings to distribute load effectively, and enable caching for frequent queries. Optimize text-based retrieval with BM25 tuning and custom analyzers for better relevance. Regularly monitor cluster health, index size, and query performance using OpenSearch Dashboards and adjust configurations accordingly.

Google Vertex AI Gemini 2.0 Flash Thinking optimization tips

Gemini 2.0 Flash Thinking is designed for rapid yet thoughtful responses in RAG systems. Optimize retrieval by focusing on high-confidence document matching, reducing unnecessary data processing. Keep prompts structured, providing key details upfront while avoiding excessive context. Adjust temperature settings (0.1–0.3) to fine-tune response diversity. Use caching to reduce API overhead for repeated queries. Take advantage of Google Cloud’s GPU-accelerated processing to improve throughput. If using Flash Thinking alongside larger models, assign it to medium-complexity reasoning tasks that require faster turnaround than Pro models but more depth than standard Flash.

IBM slate-125m-english-rtrvr optimization tips

To optimize the IBM slate-125m-english-rtrvr for Retrieval-Augmented Generation (RAG), ensure that your document retrieval system is fine-tuned with domain-specific data to improve relevance. Utilize embeddings effectively by implementing cosine similarity for efficient nearest neighbor searches, and consider applying caching mechanisms to store frequently accessed documents. Additionally, experiment with various query augmentation techniques, like rephrasing or adding related keywords, to enhance retrieval performance. Monitor and analyze retrieval metrics (such as precision and recall) to iteratively refine your setup, and if possible, implement an ensemble approach by integrating multiple retrieval models to boost diversity in retrieved content. Finally, regularly update your corpus to reflect current knowledge and trends.

By implementing these tips across your components, you'll be able to enhance the performance and functionality of your RAG system, ensuring it’s optimized for both speed and accuracy. Keep testing, iterating, and refining your setup to stay ahead in the ever-evolving world of AI development.

RAG Cost Calculator: A Free Tool to Calculate Your Cost in Seconds

Estimating the cost of a Retrieval-Augmented Generation (RAG) pipeline involves analyzing expenses across vector storage, compute resources, and API usage. Key cost drivers include vector database queries, embedding generation, and LLM inference.

RAG Cost Calculator is a free tool that quickly estimates the cost of building a RAG pipeline, including chunking, embedding, vector storage/search, and LLM generation. It also helps you identify cost-saving opportunities and achieve up to 10x cost reduction on vector databases with the serverless option.

Calculate your RAG cost now.

Calculate your RAG cost

What Have You Learned?

By diving into this tutorial, you’ve unlocked the magic of building a RAG system from the ground up! You learned how LangChain acts as the glue, seamlessly connecting your workflow by orchestrating interactions between OpenSearch (your powerful vector database), Google Vertex AI’s Gemini 2.0 Flash (the lightning-fast LLM), and IBM’s slate-125m-english-rtrvr (the embedding model that transforms text into searchable vectors). Together, these tools form a dynamic pipeline: LangChain manages the flow, OpenSearch stores and retrieves context-rich data at scale, Gemini generates human-like responses, and IBM’s model ensures your queries and documents are embedded with precision. You saw firsthand how these components collaborate to turn raw data into actionable insights, whether you’re building a chatbot, a research assistant, or a knowledge hub. Plus, you picked up pro tips like optimizing chunk sizes for embeddings and balancing speed with accuracy—skills that’ll save you time and resources!

But wait, there’s more! You also discovered how to estimate costs upfront using the free RAG cost calculator, empowering you to plan smarter and scale confidently. Now that you’ve seen the pieces in action, it’s your turn to experiment. Tweak parameters, explore hybrid search strategies in OpenSearch, or swap models to match your use case. The possibilities are endless, and every iteration brings you closer to building something truly unique. So fire up your IDE, embrace the trial-and-error process, and let your creativity run wild. You’ve got the tools, the know-how, and the momentum—go build the future of intelligent applications, one RAG-powered solution at a time! 🚀

Further Resources

🌟 In addition to this RAG tutorial, unleash your full potential with these incredible resources to level up your RAG skills.

How to Build a Multimodal RAG | Documentation
How to Enhance the Performance of Your RAG Pipeline
Graph RAG with Milvus | Documentation
How to Evaluate RAG Applications - Zilliz Learn
Generative AI Resource Hub | Zilliz

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