fyntr 0.3.1

About

Fyntr (/ˈfɪn.tər/) is a minimal forward proxy that smooths bursts of outbound TLS traffic, stabilizing connections on constrained networks. No server-side changes required, no auth, no inspection.

Fyntr starts with a small memory profile right after startup (~1-2MB peak memory footprint on macOS via /usr/bin/time -l, and ~1MB private memory on Windows) and uses an actor-driven scheduler to relay traffic transparently, making bursty workloads more stable and reliable without terminating TLS.

Internals

• Traffic shaping: Prevents burst congestion by interleaving packets via Deficit Round-Robin (DRR) scheduling.
• Adaptive quantum tuning: Optimizes quantum size via packet size statistics to reduce latency spikes and improve throughput.
• FD limit guard: Validates file descriptor limits against max connection settings.
• DoS guardrails: Caps request line/header sizes and per-flow queue buffering to suppress memory growth.

Quick Start

1. Install and run Fyntr:

   Install the crates.io release and run it locally (defaults to port 9999).

   cargo install fyntr
   fyntr
   

   Or build from source:

   cargo run --release
   

   Override defaults via CLI flags or env vars:

   cargo run --release -- --port 8080 --max-connections 512
   
   # Or use environment variables
   FYNTR_PORT=8080 FYNTR_MAX_CONNECTIONS=512 cargo run --release
   

   By default, Fyntr caps concurrent connections at 1000 (set 0 for unlimited).

2. Configure Your Environment:

   Export the following environment variables in a separate terminal.

   export HTTPS_PROXY=http://127.0.0.1:9999 
   

   This configuration affects not only aws-cli but also various tools that use libcurl, including git, brew, wget, and more.

3. Verify It Works:

   You can test the connection with a simple curl command.

   curl https://ifconfig.me
   

Library Usage

Requires actix-rt and anyhow in your application's dependencies. For logging, add env_logger (optional but recommended).

use fyntr::run;

#[actix_rt::main]
async fn main() -> anyhow::Result<()> {
    // Optional: enables logs via RUST_LOG (e.g., RUST_LOG=info).
    env_logger::init();

    let handle = run::server()
        .bind("127.0.0.1")
        .port(0) // 0 lets the OS pick an available port
        .max_connections(512)
        .background()
        .await?;

    println!("Fyntr listening on {}", handle.listen_addr());

    // ... run your app ...

    handle.shutdown().await?;
    Ok(())
}

CLI Options

Server

CONNECT Policy

Why Fyntr?

Cloud automation tools such as Terraform spawn bursts of TCP connections that rapidly open and close.

When many flows send data simultaneously, they can create short traffic spikes that overwhelm low-capacity routers, especially consumer NAT devices. This can cause CPU interrupts to be too high and make the network feel unresponsive.

Rather than relying on connection pooling, Fyntr regulates the traffic itself. Its scheduler uses DRR to distribute sending opportunities across active flows fairly, so packet bursts from many parallel flows get interleaved instead of letting them fire all at once.

This smoothing reduces CPU pressure on routers during connection storms. This effect is most critical when scheduling overhead, rather than bandwidth, is the primary bottleneck.

Limitations

In certain environments, upload throughput can be reduced due to DRR scheduling, depending on network conditions.

Usage with Terraform

Example: AWS Provider

# Set environment variables
export HTTPS_PROXY=http://127.0.0.1:9999

# Standard usage
terraform apply

# Or use aws-vault wrapper
aws-vault exec my-profile -- terraform apply