mini-balancer

A toy and mini load-balancer.

Disclaimer

This is just a toy project of mine, only meant to serve as something fun for me to build with Rust. I do not intend to maintain nor make it production-ready at all.

Description

mini-balancer is a simple connection-based, transport-level, TCP-only, mini load-balancer, where a frontend listens for TCP connections and then forwards them to one of the backends.

As an example, one may have more than one instance of a given application offering a TCP server to many clients and wants to distribute connections among such instances.

Balancing Algorithms

The only balancing algorithm implemented thus far is a simplified round-robin, where a frontend receives incoming connection and then forwards them to a given sequence of n backends (b_1, ..., b_n) in a cyclical manner, such that:

• the first connection c_1 goes to b_1,
• ...
• the nth connection c_n goes to b_n,
• the (n+1)th connection c_n+1 goes again to b_1 and so the process forever repeats.

Configuration Schema

An informal description of the TOML configuration schema is as follows:

[frontend]
bind_on = "<IP:PORT>"

[[frontend.backend]]
forward_to = "<IP:PORT>"

Examples

Balancing Connections Between Two Backends

Let's consider we have two instances of an application listening for connections on 127.0.0.1:8080 and 127.0.0.1:9090, and we want to have a single end-point on 127.0.0.1:7070 where all connections will be received and then distributed among our instances.

For simplicity, let's simulate our instances as echo servers with socat:

λ socat -v tcp-l:8080,fork exec:'/bin/cat'

λ socat -v tcp-l:9090,fork exec:'/bin/cat'

Assuming we have saved the following configuration file as mini-balancer.local.toml:

[frontend]
bind_on = "127.0.0.1:7070"

[[frontend.backend]]
forward_to = "127.0.0.1:8080"

[[frontend.backend]]
forward_to = "127.0.0.1:9090"

We can then start mini-balancer as:

λ mini-balancer -v -c mini-balancer.local.toml

To simulate a client, we once again rely on socat to send a message as:

λ echo "first connection" | socat tcp:127.0.0.1:7070 -

λ echo "second connection" | socat tcp:127.0.0.1:7070 -

The first connection should go to the first backend, whereas the second connection should go to the second backend. The logs should look like as follows:

May 08 14:18:45.305  INFO frontend{local_address=127.0.0.1:7070}: mini_balancer::balancing::frontend: listening for connections
May 08 14:19:01.488  INFO handle_connection{peer_address=127.0.0.1:49438}: mini_balancer::balancing::frontend: serving connection
May 08 14:19:01.488  INFO handle_connection{peer_address=127.0.0.1:49438}:through{target_address=127.0.0.1:8080}: mini_balancer::balancing::middleware::client: opened client connection
May 08 14:19:01.490  INFO handle_connection{peer_address=127.0.0.1:49438}: mini_balancer::balancing::frontend: served connection
May 08 14:19:13.622  INFO handle_connection{peer_address=127.0.0.1:49444}: mini_balancer::balancing::frontend: serving connection
May 08 14:19:13.623  INFO handle_connection{peer_address=127.0.0.1:49444}:through{target_address=127.0.0.3:9090}: mini_balancer::balancing::middleware::client: opened client connection
May 08 14:19:13.627  INFO handle_connection{peer_address=127.0.0.1:49444}: mini_balancer::balancing::frontend: served connection

Lastly, if we open a third connection, it should again go to the first backend.

Instructions

• Minimum Supported Rust Version (MSRV): 1.51.0.

Linting

cargo clippy

Building

cargo build

Testing

cargo test