Apex TCP Proxy

A lightweight, high-performance TCP reverse proxy in Rust with dynamic backend health checks and round-robin load balancing. Apex ensures requests are forwarded only to healthy backends.

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Features

• TCP Proxy: Forward TCP traffic from a listening port to multiple backend servers.
• Round-Robin Load Balancing: Requests are distributed evenly across all healthy backends.
• Dynamic Health Checks: Periodically checks backend availability and updates routing automatically.
• Hot Config Reloading: Detects changes to config.toml and updates backends and load balancing in real-time.
• Async and High Performance: Built with Tokio, fully asynchronous for low-latency forwarding.

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Architecture

Client → [Apex TCP Proxy] → [Healthy Backend(s)]

• The proxy listens on a port (default 8081) and forwards traffic to healthy backend servers.
• Backend health is checked periodically (default every 5 seconds).
• Only healthy backends are used for request forwarding.
• Supports hot config reload: changes in config.toml automatically update backend addresses and the load balancer.
• Load balancing is implemented as round-robin: requests cycle through available healthy backends.

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Configuration

Create a config.toml file:

backend_addrs = ["127.0.0.1:9000", "127.0.0.1:9001"]

• Add or remove backend addresses as needed.
• The proxy automatically reloads this file when modified.

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Running Apex

# Run your backend(s) first, e.g.:
python3 -m http.server 9000
python3 -m http.server 9001

# Run the proxy
cargo run

• The proxy listens on 127.0.0.1:8081 by default.
• Open another terminal to test:

curl http://127.0.0.1:8081

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Logs & Output

Example Log Snippet

2025-10-03T05:49:40 INFO apex: Loaded backend addresses: ["127.0.0.1:9000", "127.0.0.1:9001"]
2025-10-03T05:49:40 INFO apex: Proxy listening on 127.0.0.1:8081
2025-10-03T05:50:05 INFO apex::proxy_utils: Health check 127.0.0.1:9000 => alive: true
2025-10-03T05:50:05 INFO apex::proxy_utils: Health check 127.0.0.1:9001 => alive: false
2025-10-03T05:50:43 INFO apex: Accepted connection from 127.0.0.1:45688
2025-10-03T05:50:43 INFO apex: Connected to backend: 127.0.0.1:9000
2025-10-03T05:50:43 INFO apex: Forwarding data between 127.0.0.1:45688 and 127.0.0.1:9000

Load Balancing Behavior

• Round-robin ensures even distribution across healthy backends.
• Backends marked unhealthy by health checks are skipped automatically.
• When backends recover, they are re-added to the rotation automatically.

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Notes & Tips

• Ensure backends are running before sending requests to the proxy.
• For debugging, check logs for alive: true/false to see which backends are used.
• Config reload works in real-time, so you can add/remove backends on the fly.

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Dependencies

• Rust 1.80+
• Tokio (async runtime)
• tracing & tracing-subscriber (logging)
• notify (config file watching)

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License

MIT License