LitServe: The Future of Scalable AI Model Serving

Introduction

While FastAPI is good for implementing RESTful APIs, it wasn’t specifically designed to handle the complex requirements of serving machine learning models. FastAPI’s support for asynchronous calls is primarily at the web level and doesn’t extend deeply into the model prediction layer. This limitation poses challenges because AI model predictions are resource-intensive operations that need to be configured to optimize performance, especially when dealing with modern large language models (LLMs).

Deploying and serving machine learning models at scale can be as challenging as even building the models themselves. This is where LitServe, an open-source, flexible serving engine built on top of FastAPI, comes into play. LitServe simplifies the process of serving AI models by providing powerful features like batching, streaming, GPU acceleration, and autoscaling. In this article, we will introduce LitServe, delve into its functionalities, and how it can be used to build scalable, high-performance AI servers.

Learning Objectives

• Understand how to easily set up and serve AI models using LitServe.
• Learn how to use batching, streaming, and GPU acceleration to better AI model performance.
• Gain hands-on experience with a toy example, building a simple server to serve AI models.
• Explore features to optimize model serving for high throughput and scalability.

This article was published as a part of the Data Science Blogathon.

What is Model Serving?

In machine learning, deploying and serving models effectively helps to make predictions in real-time applications when deployed to production. Model serving refers to the process of taking a trained machine-learning model and making it available for use in production environments. This can involve exposing the model through APIs so that users or applications can make inference and receive predictions.

The importance of model serving affects the responsiveness and scalability of machine learning applications. Several challenges arise during the deployment, like with large language models (LLMs) that demand high computational resources. These challenges include latency in response times, the need for efficient resource management, and ensuring that models can handle varying loads without degradation in performance. Developers need robust solutions that simplify the serving process while maximizing efficiency. This is where specialized tools like LitServe come in with features designed to streamline model serving and performance.

What is LitServe?

LitServe is an open-source model server designed to provide a fast, flexible, and scalable serving of AI models. By handling complex engineering tasks like scaling, batching, and streaming, eliminates the need to rebuild FastAPI servers for each model. You can use LitServe to deploy models on local machines, cloud environments, or high-performance computing with multiple GPUs.

Key Features of LitServe

Let us explore key features of LitServe:

Faster Model Serving: LitServe is optimized for performance, ensuring models serve better than traditional methods and even better.

Multi-GPU Support: In cases where the server has multiple GPUS, It leverages the power of multiple GPUs to parallelize model serving, reducing latency.

Batching and Streaming: LitServe can serve multiple calls simultaneously using batching techniques or streaming the response without overloading the server.

LitServe brags about multiple features from authentication to OpenAI specs with features to cater to complex AI workloads.

Getting Started with LitServe

To illustrate how LitServe works, we’ll begin with a simple example and then move on to deploying a more realistic AI server for image captioning using models from Hugging Face. The first step is to install LitServe:

pip install litserve

Defining a Simple API with LitServe

LitServe simplifies the process of defining how your model interacts with external calls. The LitAPI class handles incoming calls and returns model predictions. Here’s how you can set up a simple API:

import litserve as ls

class SimpleLitAPI(ls.LitAPI):
    def setup(self, device):
        self.model1 = lambda x: x**2
        self.model2 = lambda x: x**3

    def decode_request(self, request):
        return request["input"]

    def predict(self, x):
        squared = self.model1(x)
        cubed = self.model2(x)
        output = squared + cubed
        return {"output": output}

    def encode_response(self, output):
        return {"output": output}

Let’s break down the class:

• setup: Initializes the models or resources your server needs. In this example, we define two simple functions that simulate models.
• decode_request: Converts incoming calls into a format that the model can process. It extracts the input from the request payload.
• predict: Runs the model(s) to make predictions. Here, it calculates the square and cube of the input and sums them.
• encode_response: Converts the model’s output into a response format that can be sent back to the client.

After defining your API, you can run the server by instantiating your API class and passing it to LitServer:

if __name__ == "__main__":
    api = SimpleLitAPI()
    server = ls.LitServer(api, accelerator="gpu") # accelerator can also be 'auto'
    server.run(port=8000)

This command will launch the server to handle inferences with GPU acceleration.

Serving a Vision Model with LitServe

To showcase LitServe’s full potential, let’s deploy a realistic AI server that performs image captioning using a model from Hugging Face. This example will show the way LitServe handles more complex tasks and features like GPU acceleration.

Implementing the Image Captioning Server

First, import the necessary libraries and define helper functions:

import requests
import torch
from PIL import Image
from transformers import VisionEncoderDecoderModel, ViTImageProcessor, GPT2TokenizerFast
from tqdm import tqdm
import urllib.parse as parse
import os

# LitServe API Integration
import litserve as ls


# Verify URL function
def check_url(string):
    try:
        result = parse.urlparse(string)
        return all([result.scheme, result.netloc, result.path])
    except:
        return False


# Load an image from a URL or local path
def load_image(image_path):
    if check_url(image_path):
        return Image.open(requests.get(image_path, stream=True).raw)
    elif os.path.exists(image_path):
        return Image.open(image_path)

Next, define the LitAPI class for image captioning:

# HuggingFace API class for image captioning
class ImageCaptioningLitAPI(ls.LitAPI):
    def setup(self, device):
        # Assign available GPU or CPU
        self.device = "cuda" if torch.cuda.is_available() else "cpu"

        # Load the ViT Encoder-Decoder Model
        model_name = "nlpconnect/vit-gpt2-image-captioning"
        self.model = VisionEncoderDecoderModel.from_pretrained(model_name).to(self.device)
        self.tokenizer = GPT2TokenizerFast.from_pretrained(model_name)
        self.image_processor = ViTImageProcessor.from_pretrained(model_name)

    # Decode payload to extract image URL or path
    def decode_request(self, request):
        return request["image_path"]

    # Generate image caption
    def predict(self, image_path):
        image = load_image(image_path)

        # Preprocessing the Image
        img = self.image_processor(image, return_tensors="pt").to(self.device)

        # Generating captions
        output = self.model.generate(**img)

        # Decode the output to generate the caption
        caption = self.tokenizer.batch_decode(output, skip_special_tokens=True)[0]

        return caption

    # Encode the response back to the client
    def encode_response(self, output):
        return {"caption": output}

For this very use case:

• setup: Loads the pre-trained image captioning model and associated tokenizer and processor, moving them to the device (CPU or GPU).
• decode_request: Extracts the image path from the incoming call.
• predict: Processes the image, generates a caption using the model, and decodes it.
• encode_response: Formats the caption into a JSON response.

# Running the LitServer
if __name__ == "__main__":
    api = ImageCaptioningLitAPI()
    server = ls.LitServer(api, accelerator="auto", devices=1, workers_per_device=1)
    server.run(port=8000)

This command will launch the server, automatically detecting available accelerators and configuring devices. Find the entire code here.

Testing the Server

With the server running, you can test it by sending POST requests with an image_path (either a URL or a local file path) in the payload. The server will return a generated caption for the image.

Example: 1

Image:

Generated Caption: “a view from a boat of a beach with a large body of water”

Example 2:

Image: 

Generated Caption: “a man in a suit and tie holding a red and white flag”

You can use the Colab notebook provided on GitHub to test the server directly. You can explore as the possibilities are endless.

Enhancing Performance with Advanced Features

LitServe allows you to optimize your server’s performance by utilizing its advanced features:

• Batching: Include max_batch_size=2 in LitServer to process multiple calls simultaneously, improving throughput.
• Streaming: Set stream as True to handle large inputs efficiently without overloading the server.
• Device Management: Specify GPU IDs in devices for control over hardware, especially useful in multi-GPU setups.

For a detailed list of features and configurations, check the official documentation: LitServe Features

Why Choose LitServe?

LitServe effectively tackles the unique challenges of deploying large language models. Unlike traditional model serving methods, it is built for high-performance inference, enabling developers to serve models with minimal latency and maximum throughput. Here’s why you should consider LitServe for your model serving needs:

• Scalability: LitServe is built to scale seamlessly with your application. It can handle multiple calls together, efficiently distributing computational resources based on demand.
• Optimized Performance: It offers features like batching, which allows for processing calls at the same time, reducing the average response time. This is beneficial when serving large language models that need resources.
• Ease of Use: LitServe simplifies the deployment of machine learning models with the setup. Developers can quickly transition from model training to production with faster iterations and deployments.
• Support for Advanced Features: LitServe includes support for GPU acceleration and streaming, allowing for efficient handling of real-time data and complex model architectures. This ensures that your applications can maintain high performance, even under heavy loads.

Conclusion

LitServe provides a powerful, flexible, and efficient way for serving AI models. By abstracting away the complexities of scaling, batching, and hardware, it allows developers to focus on building high-quality AI solutions without worrying about the intricacies of deployment. Whether you’re deploying simple models or complex, multimodal AI systems, LitServe’s robust features and ease of use make it a good choice for both beginners and experienced practitioners.

Key Takeaways

• LitServe streamlines the process of serving AI models, eliminating the need to rebuild servers for each model.
• Features like batching, streaming, and multi-GPU support enhances model serving performance.
• LitServe adapts to environments, from local machines to multi-GPU servers, making it suitable for projects of all sizes.
• LitServe handles complex AI workloads by supporting authentication, compliance standards, and more.

References and Links

• GitHub Link: Image Captioning-ViT
• GitHub: LitServe
• Overview: Serve Models
• Features: LitServe

Frequently Asked Questions

The media shown in this article is not owned by Analytics Vidhya and is used at the Author’s discretion.