Zero-Copy TCP Load Balancer

Small TCP load balancer written in Go.

The proxy listens on :8123, forwards traffic to several backends, and exposes Prometheus metrics on :8081/metrics.

What it does

• Forwards TCP connections to backends with round-robin selection.
• Copies traffic in both directions with io.Copy
• Runs a background health check loop to keep only reachable backends.
• Exposes basic metrics:
  • proxy_requests_total
  • proxy_active_servers

Project layout

• main.go: starts the TCP listener and metrics endpoint.
• proxy/tcp.go: handles bidirectional proxying between client and backend.
• proxy/balancer.go: round-robin logic and backend health checks.
• docker-compose.yml: local test setup (3 Nginx backends + Prometheus + Grafana).

Run locally

1. Start the local stack:

docker compose up -d

2. Run the proxy:

go run main.go

3. Send traffic through the proxy:

curl http://localhost:8123

Metrics and dashboards

• App metrics: http://localhost:8081/metrics
• Prometheus: http://localhost:9090
• Grafana: http://localhost:3000 (default login: admin/admin)

Notes

• This project is Linux-oriented because the zero-copy behavior depends on kernel capabilities.
• If all backends are down, new client connections are rejected until a backend becomes healthy again.