Your First Federated Learning Project

This tutorial walks you through creating your first federated learning (FL) project using Syft-Flwr, from setting up the environment to running your first FL training session.

What You’ll Build

You’ll create a diabetes prediction model trained collaboratively across multiple data owners without centralizing their data. The complete project structure will look like:

fl-diabetes-prediction/
├── fl_diabetes_prediction/
│   ├── __init__.py
│   ├── client_app.py   # Defines your ClientApp
│   ├── server_app.py   # Defines your ServerApp
│   └── task.py         # Defines your model, training and data loading
├── pyproject.toml      # Project metadata and dependencies
└── README.md

Prerequisites

Python 3.12 or later
Basic understanding of PyTorch and machine learning
Access to at least 2 machines or environments (for data owners)

Install Syft-Flwr

Install the Syft-Flwr framework:

pip install syft-flwr

Or install from source:

pip install "git+https://github.com/OpenMined/syft-flwr.git@main"

Create Project Structure

Create your project directory and files:

mkdir -p fl-diabetes-prediction/fl_diabetes_prediction
cd fl-diabetes-prediction
touch fl_diabetes_prediction/__init__.py
touch fl_diabetes_prediction/client_app.py
touch fl_diabetes_prediction/server_app.py
touch fl_diabetes_prediction/task.py
touch pyproject.toml

Define the Model and Training Logic

Create your neural network model in task.py:

import torch
import torch.nn as nn
import torch.optim as optim
from torch.utils.data import DataLoader, TensorDataset
from collections import OrderedDict

class Net(nn.Module):
    def __init__(self, input_dim=6):
        super(Net, self).__init__()
        self.layer1 = nn.Sequential(
            nn.Linear(input_dim, 32),
            nn.BatchNorm1d(32),
            nn.LeakyReLU(0.1),
            nn.Dropout(0.2),
        )
        self.layer2 = nn.Sequential(
            nn.Linear(32, 24),
            nn.BatchNorm1d(24),
            nn.LeakyReLU(0.1),
            nn.Dropout(0.25),
        )
        self.layer3 = nn.Sequential(
            nn.Linear(24, 16),
            nn.BatchNorm1d(16),
            nn.LeakyReLU(0.1)
        )
        self.output_layer = nn.Sequential(
            nn.Linear(16, 1),
            nn.Sigmoid()
        )

    def forward(self, x):
        x = self.layer1(x)
        x = self.layer2(x)
        x = self.layer3(x)
        x = self.output_layer(x)
        return x

def train(model, train_loader, local_epochs=1):
    criterion = nn.BCELoss()
    optimizer = optim.Adam(model.parameters(), lr=0.001, weight_decay=0.0005)
    model.train()
    
    for epoch in range(local_epochs):
        for inputs, labels in train_loader:
            optimizer.zero_grad()
            outputs = model(inputs)
            loss = criterion(outputs, labels)
            loss.backward()
            optimizer.step()

def evaluate(model, data_loader):
    model.eval()
    criterion = nn.BCELoss()
    running_loss = 0.0
    correct = 0
    total = 0
    
    with torch.no_grad():
        for inputs, labels in data_loader:
            outputs = model(inputs)
            loss = criterion(outputs, labels)
            running_loss += loss.item() * inputs.size(0)
            predicted = (outputs > 0.5).float()
            total += labels.size(0)
            correct += (predicted == labels).sum().item()
    
    epoch_loss = running_loss / len(data_loader.dataset)
    epoch_acc = correct / total
    return epoch_loss, epoch_acc

def get_weights(model):
    return [val.cpu().numpy() for _, val in model.state_dict().items()]

def set_weights(model, parameters):
    params_dict = zip(model.state_dict().keys(), parameters)
    state_dict = OrderedDict({k: torch.tensor(v) for k, v in params_dict})
    model.load_state_dict(state_dict, strict=True)

Implement the Data Loading

Add the data loading function in task.py. This is the key difference from standard Flower—it loads data from SyftBox:

def load_syftbox_dataset():
    """Load dataset from SyftBox private data directory"""
    import pandas as pd
    from syft_flwr.utils import get_syftbox_dataset_path
    
    # Get the private dataset path set by SyftBox
    data_dir = get_syftbox_dataset_path()
    
    # Load train and test data
    train_df = pd.read_csv(data_dir / "train.csv")
    test_df = pd.read_csv(data_dir / "test.csv")
    
    # Process and return DataLoaders
    return dataset_processing(train_df, test_df)

The get_syftbox_dataset_path() function retrieves the path to private data that only the data owner can access. This ensures data never leaves the owner’s machine.

Create the Client Application

Define how clients participate in training in client_app.py:

from flwr.client import ClientApp, NumPyClient
from flwr.common import Context

from fl_diabetes_prediction.task import (
    Net,
    evaluate,
    get_weights,
    set_weights,
    train,
    load_syftbox_dataset,
)

class FlowerClient(NumPyClient):
    def __init__(self, net, trainloader, testloader):
        self.net = net
        self.trainloader = trainloader
        self.testloader = testloader

    def fit(self, parameters, config):
        set_weights(self.net, parameters)
        train(self.net, self.trainloader)
        return get_weights(self.net), len(self.trainloader), {}

    def evaluate(self, parameters, config):
        set_weights(self.net, parameters)
        loss, accuracy = evaluate(self.net, self.testloader)
        return loss, len(self.testloader), {"accuracy": accuracy}

def client_fn(context: Context):
    # Load the private dataset from SyftBox
    train_loader, test_loader = load_syftbox_dataset()
    net = Net()
    return FlowerClient(net, train_loader, test_loader).to_client()

app = ClientApp(client_fn=client_fn)

Create the Server Application

Define the aggregation strategy in server_app.py:

from flwr.common import Context, ndarrays_to_parameters
from flwr.server import ServerApp, ServerAppComponents, ServerConfig
from syft_flwr.strategy import FedAvgWithModelSaving
from pathlib import Path
import os

from fl_diabetes_prediction.task import Net, get_weights

def weighted_average(metrics):
    accuracies = [num_examples * m["accuracy"] for num_examples, m in metrics]
    examples = [num_examples for num_examples, _ in metrics]
    return {"accuracy": sum(accuracies) / sum(examples)}

def server_fn(context: Context):
    # Initialize the model
    net = Net()
    params = ndarrays_to_parameters(get_weights(net))
    
    # Set up model save path
    output_dir = os.getenv("OUTPUT_DIR", Path.home() / ".syftbox/rds/")
    save_path = Path(output_dir) / "weights"
    
    # Configure the aggregation strategy
    strategy = FedAvgWithModelSaving(
        save_path=save_path,
        fraction_fit=1.0,
        fraction_evaluate=1.0,
        min_available_clients=2,
        min_fit_clients=2,
        min_evaluate_clients=2,
        initial_parameters=params,
        evaluate_metrics_aggregation_fn=weighted_average,
    )
    
    num_rounds = context.run_config["num-server-rounds"]
    config = ServerConfig(num_rounds=num_rounds)
    
    return ServerAppComponents(config=config, strategy=strategy)

app = ServerApp(server_fn=server_fn)

FedAvgWithModelSaving is a custom strategy that saves the global model to disk after each training round, making it easy to track progress and recover from failures.

Configure the Project

Create pyproject.toml with project metadata and dependencies:

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

[project]
name = "fl-diabetes-prediction"
version = "1.0.0"
requires-python = ">=3.12"
description = "Federated Learning for Diabetes Prediction"
license = "Apache-2.0"
dependencies = [
    "flwr-datasets>=0.5.0",
    "torch>=2.8.0",
    "imblearn",
    "pandas",
    "scikit-learn==1.6.1",
    "loguru",
    "syft_flwr",
]

[tool.flwr.app]
publisher = "YourName"

[tool.flwr.app.components]
serverapp = "fl_diabetes_prediction.server_app:app"
clientapp = "fl_diabetes_prediction.client_app:app"

[tool.flwr.app.config]
num-server-rounds = 3
min-available-clients = 2
min-fit-clients = 2
min-evaluate-clients = 2
fraction-fit = 1.0
fraction-evaluate = 1.0

Bootstrap the FL Project

Before running, bootstrap your project with Syft-Flwr metadata:

import syft_flwr
from pathlib import Path

project_path = Path("./fl-diabetes-prediction")
aggregator_email = "[email protected]"  # Data scientist email
datasite_emails = ["[email protected]", "[email protected]"]  # Data owner emails

syft_flwr.bootstrap(
    project_path,
    aggregator=aggregator_email,
    datasites=datasite_emails
)

This creates a main.py file and updates pyproject.toml with:

Unique app name for this FL run

List of participating data owners

Aggregator (data scientist) email

Test with Simulation (Optional)

Before running on real data, test locally with mock data:

flwr run ./fl-diabetes-prediction

Or test with Syft-Flwr simulation:

syft_flwr.run(
    project_path,
    mock_paths=["path/to/mock1", "path/to/mock2"]
)

Submit to Data Owners

Data scientists submit the FL project to data owners for approval:

import syft_rds as sy

# Connect to data owner's datasite
do1_client = sy.init_session(
    host="[email protected]",
    email="[email protected]"
)

# Submit the job
do1_client.job.submit(
    name="fl-diabetes-prediction",
    user_code_path=project_path,
    dataset_name="pima-indians-diabetes-database",
    entrypoint="main.py",
)

Run the FL Server

Once data owners approve and run the client code, start the aggregation server:

# Submit to yourself to run the server
ds_client = sy.init_session(
    host="[email protected]",
    email="[email protected]"
)

job = ds_client.job.submit(
    name="fl-diabetes-prediction-server",
    user_code_path=project_path,
    entrypoint="main.py",
)

# Approve and run
ds_client.job.approve(job)
ds_client.run_private(job, blocking=True)

Monitor Results

The aggregated model weights are saved after each round in the weights/ directory:

weights/
├── parameters_round_1.safetensors
├── parameters_round_2.safetensors
└── parameters_round_3.safetensors

View training logs:

ds_client.job.show_logs(job)

Key Differences from Standard Flower

Syft-Flwr requires only minimal changes to a standard Flower project:

Data Loading: Use load_syftbox_dataset() instead of loading from public datasets
Bootstrap Step: Run syft_flwr.bootstrap() to configure participants
Communication: Messages are exchanged via file sync instead of network connections

What’s Next?

Common Issues

FileNotFoundError: DATA_DIR does not exist

This means the DATA_DIR environment variable is not set. Make sure:

You’re running the code through SyftBox job execution
The dataset is properly registered with SyftBox
You’re using load_syftbox_dataset() in your client code

No clients connecting to server

Check that:

Data owners have approved the job requests
All participants are running their respective code
The app_name in pyproject.toml matches across all participants
SyftBox is running and syncing files properly

Model weights not saving

Verify:

The OUTPUT_DIR environment variable points to a writable location
You’re using FedAvgWithModelSaving strategy
The save path directory exists and has write permissions

Get Started

Core Concepts

Tutorials

Guides

Your First Federated Learning Project

What You’ll Build

Prerequisites

Key Differences from Standard Flower

What’s Next?

Common Issues

Build docs developers (and LLMs) love

Get Started

Core Concepts

Tutorials

Guides

​What You’ll Build

​Prerequisites

​Key Differences from Standard Flower

​What’s Next?

​Common Issues

Build docs developers (and LLMs) love

What You’ll Build

Prerequisites

Key Differences from Standard Flower

What’s Next?

Common Issues