Implement least connection load balancing algorithm

[Kevin301099]

[beamandala]

Hi, is this issue available to work on?

[eaufavor]

Our load balancing traits are public https://docs.rs/pingora-load-balancing/latest/pingora_load_balancing/selection/trait.BackendSelection.html.

@beamandala if you like to implement it, go for it. The code doesn't have to be in our libraries for people to use. Still, PRs are always welcomed.

[beamandala]

Thanks! Correct me if I'm wrong but if I wanted to make a pull request adding the least connection load balancing algorithm to pingora, I'm assuming I would have to follow a pattern similar to the weighted selection algorithm where I would add a connections field to the Backend struct and place the actual algorithm implementation in its own file?

[eaufavor]

add a connections field to the Backend struct

I imagine you will track the connection info in your own struct. like ketama.

I don't think the Backend itself needs to be changed.