Load Balancer

A TCP load balancer written in Go as a system design learning project.

Architecture

The project is composed of four layered packages:

Listener → Proxy → Router → Backend

• listener — accepts incoming TCP connections and dispatches each to the proxy in a goroutine
• proxy — forwards traffic between the client and the selected backend using bidirectional byte copying
• router — maps a local address to a backend; the extension point for load balancing strategies
• backend — represents a single upstream server

Getting Started

Prerequisites

• Go 1.24+

Run

go run main.go

The load balancer listens on port 8080 by default and forwards traffic to localhost:80.

Build

go build -o load-balancer .
./load-balancer

Project Structure

.
├── main.go          # entry point — wires all components together
├── backend/
│   └── backend.go   # upstream server representation
├── router/
│   └── router.go    # routing logic (address → backend)
├── proxy/
│   └── proxy.go     # TCP proxy (bidirectional copy)
└── listener/
    └── listener.go  # TCP listener

Extending

To add a load balancing algorithm (round-robin, least-connections, etc.), update router/router.go — it implements the RouterIO interface consumed by the proxy:

type RouterIO interface {
    Route(address string) BackendIO
}

Multiple backends can be registered and the Route method can select among them using any strategy.