🛡️ FlowGuard: Next-Generation Adaptive Concurrency Control & Backpressure for Rust

🎯 About the Project

Created and developed by: Cleiton Augusto Correa Bezerra

FlowGuard is a next-generation load control library. Unlike static rate limiters, FlowGuard uses congestion control algorithms (TCP Vegas) to dynamically adjust load limits based on real latency and system health.

🚀 The Innovation: Why FlowGuard?

Setting a fixed limit (e.g., "maximum 100 connections") is a trap in modern systems:

• Limit too high: System crashes (Cascading Failure) before reaching the limit
• Limit too low: Wasted hardware and refusal of legitimate traffic

FlowGuard solves this with:

✅ Auto-tuning:

Observes RTT (Round Trip Time). If latency rises, it reduces concurrency. If the system is fast, it expands capacity.

✅ Native Resilience:

Protects databases and external services from overload.

✅ Zero-Cost Abstractions:

Built with atomic operations in Rust for extreme performance.

✅ Dynamic Semaphore Adjustment:

Unlike static implementations, FlowGuard's semaphore adjusts in real-time with the Vegas algorithm.

📦 Installation

Add this to your Cargo.toml:

toml [dependencies]

Core Version

flow-guard = "0.2.1"

With Axum 0.8 / Tower support

flow-guard = { version = "0.2.1", features = ["axum", "tower"] } 🚀 Quick Start Basic Usage rust use flow_guard::{FlowGuard, VegasStrategy}; use std::time::Duration; use tokio::time::sleep; use std::sync::Arc;

#[tokio::main] async fn main() { // Create Vegas strategy with initial limit of 10 let strategy = Arc::new(VegasStrategy::new(10)); let guard = FlowGuard::new(Arc::clone(&strategy));

println!("Initial limit: {}", guard.current_limit());
println!("Available permits: {}", guard.available_permits());

// Use FlowGuard to execute tasks with adaptive backpressure
let result = guard.run(async {
    sleep(Duration::from_millis(100)).await;
    Ok::<_, &str>("Task completed successfully!")
}).await;

match result {
    Ok(msg) => println!("✅ {}", msg),
    Err(err) => println!("❌ Error: {:?}", err),
}

println!("Final limit: {}", guard.current_limit()); // Adjusted dynamically!

} With Axum 0.8 rust use axum::{routing::get, Router, error_handling::HandleErrorLayer}; use flow_guard::{FlowGuardLayer, VegasStrategy, FlowError}; use tower::ServiceBuilder;

#[tokio::main] async fn main() { // Initialize with initial limit let strategy = VegasStrategy::new(10); let flow_layer = FlowGuardLayer::new(strategy);

let app = Router::new()
    .route("/api/data", get(|| async { "Hello from Protected API!" }))
    .layer(
        ServiceBuilder::new()
            .layer(HandleErrorLayer::new(|err: FlowError<std::convert::Infallible>| async move {
                // Automatically returns 503 Service Unavailable if overloaded
                err.into_response()
            }))
            .layer(flow_layer)
    );

let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
axum::serve(listener, app).await.unwrap();

} 📊 The Vegas Algorithm FlowGuard implements TCP Vegas congestion control algorithm that adjusts the concurrency limit based on the difference between expected and actual throughput:

Increases limit when system has spare capacity

Decreases limit when latency indicates congestion

Self-tuning based on real-time performance metrics

🔧 Features ✅ Dynamic Adaptation Real-time concurrency adjustment based on system health

Proactive congestion prevention

No manual tuning required

✅ Resilience Patterns Protects against cascading failures

Preserves system stability under load

Graceful degradation

✅ Production Ready Built with atomic operations for maximum performance

Zero-cost abstractions

Seamless integration with Axum/Tower ecosystem

✅ Observability Built-in metrics: current_limit() and available_permits()

Dynamic semaphore adjustment in real-time

📚 Documentation Full API documentation is available on docs.rs

🎯 Examples Check the examples/ directory:

basic_usage.rs - Basic FlowGuard usage

server_demo.rs - Axum web server example (requires axum feature)

Run examples with:

bash cargo run --example basic_usage cargo run --example server_demo --features axum,tower 📋 Changelog v0.2.1 (2024-12-27) Fixed Implement dynamic semaphore adjustment (was static in v0.2.0)

Replace tokio::sync::Semaphore with custom DynamicSemaphore

Fix Vegas strategy integration with semaphore limits

Add observability methods: current_limit() and available_permits()

Breaking Changes None (API compatible with v0.2.0)

v0.2.0 (2024-12-27) Initial public release

Vegas congestion control algorithm

Basic backpressure implementation

Axum/Tower middleware support

🤝 Contributing Contributions are the heart of the Rust community! Feel free to submit pull requests or open issues.

Please ensure:

Code follows Rust formatting standards (cargo fmt)

No clippy warnings (cargo clippy)

Tests pass (cargo test)

📄 License This project is licensed under the MIT License - see the LICENSE file for details.

Author: Cleiton Augusto Correa Bezerra Email: augusto.cleiton@gmail.com LinkedIn: cleiton-augusto-b619435b

Made with ❤️ and Rust