BalanGOl — Go Load Balancer

A production-style HTTP load balancer built in Go with Round Robin algorithm, real-time health checks, REST API for managing backends, and a live dashboard.

Architecture

                    ┌─────────────────────────────────┐
  Clients ─────────▶│  Load Balancer  :8080           │
                    │  (reverse proxy + round robin)  │
                    └────────────┬────────────────────┘
                                 │ forwards to healthy backend
                    ┌────────────▼──────────────────────┐
                    │  Backend 1   Backend 2   Backend N│
                    └───────────────────────────────────┘

                    ┌─────────────────────────────────┐
  Browser ─────────▶│  Admin API + Dashboard  :9090   │
                    │  REST API + WebSocket            │
                    └─────────────────────────────────┘

Features

• Round Robin load balancing across N backend servers
• Health checks every 10 seconds — unhealthy backends are skipped automatically
• REST API to add/remove backends at runtime (no restart needed)
• WebSocket dashboard — live status, request counts, health updates
• Atomic counters for per-backend request/error tracking
• Interface-driven balancer — swap RoundRobin for LeastConnections easily

Project Structure

loadbalancer/
├── cmd/server/main.go              # Entry point — two HTTP servers
├── internal/
│   ├── models/backend.go           # Backend model with atomic counters
│   ├── balancer/
│   │   ├── balancer.go             # Balancer interface + Registry
│   │   └── roundrobin.go           # Round Robin algorithm
│   ├── proxy/proxy.go              # httputil.ReverseProxy wrapper
│   ├── health/checker.go           # Goroutine-based health checker
│   └── server/
│       ├── api.go                  # REST API handlers
│       ├── hub.go                  # WebSocket broadcast hub
│       └── ws.go                   # WebSocket upgrade handler
└── web/index.html                  # Live dashboard

Quick Start

go mod tidy
go run ./cmd/server

Two servers start:

• :8080 — the actual load balancer (send your traffic here)
• :9090 — admin dashboard (open in browser)

API

Add a backend

curl -X POST http://localhost:9090/api/backends \
  -H "Content-Type: application/json" \
  -d '{"url": "http://localhost:3001"}'

List backends

curl http://localhost:9090/api/backends

Remove a backend

curl -X DELETE http://localhost:9090/api/backends/{id}

Stats

curl http://localhost:9090/api/stats

Testing with dummy backends

Start a few simple servers in separate terminals:

# Terminal 1
python3 -m http.server 3001

# Terminal 2
python3 -m http.server 3002

# Terminal 3
python3 -m http.server 3003

Then add them via the dashboard or API and watch requests get distributed.

Go Concepts Demonstrated

Concept	Where
httputil.ReverseProxy	proxy/proxy.go — core forwarding
Goroutines	health checker, WebSocket pumps, hub
sync/atomic	per-backend request/error counters
sync.RWMutex	backend registry, round robin list
Interfaces	Balancer interface — swappable algorithms
Channels	WebSocket hub fan-out
http.ServeMux	Go 1.22 method+path routing