#12 Weighted Round Robin Load Balancing | System Design Crash Course

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Weighted Round Robin is a load balancing algorithm that builds upon the basic Round Robin algorithm by allowing for different weights to be assigned to each server in a server pool. These weights reflect the server's capacity, capability, or performance. Servers with higher weights receive a proportionally larger share of incoming requests. Here's how Weighted Round Robin works:

1. **Server List:** Like Round Robin, Weighted Round Robin maintains a list of available servers that can handle incoming requests. Each server in the list is assigned a weight value.

2. **Request Arrival:** When a new request arrives at the load balancer, it needs to be directed to one of the servers in the list.

3. **Server Selection:** The load balancer selects the next server from the list based on the Round Robin principle. However, unlike the basic Round Robin, Weighted Round Robin takes server weights into account.

4. **Weighted Distribution:** The selected server is determined based on its weight. Servers with higher weights are selected more frequently, while those with lower weights are chosen less often. This means that servers with higher capacity or performance receive a larger share of incoming requests.

5. **Rotation and Repetition:** After handling a request, the selected server moves to the end of the server list, and the process repeats. The cycle continues, with servers selected in proportion to their assigned weights.

Key characteristics and considerations of Weighted Round Robin:

- **Capacity Consideration:** Weighted Round Robin allows load balancers to consider the capacity or capability of each server when distributing traffic. Servers with higher weights can handle more requests.

- **Proportional Load Distribution:** The load balancer ensures that the distribution of requests is proportional to the server weights. For example, a server with twice the weight of another will receive approximately twice as many requests.

- **Flexibility:** Weighted Round Robin is particularly useful when servers have different hardware specifications, processing power, or available resources. It allows you to optimize resource utilization.

- **Simplicity:** Despite the introduction of weights, Weighted Round Robin remains a relatively simple and easy-to-understand load balancing algorithm.

- **Uniform Distribution:** Weighted Round Robin helps prevent overloading of individual servers and ensures that the load is distributed evenly, even when servers have varying capacities.

- **Configuration:** Configuring the weights correctly is essential. If weights are not assigned appropriately, the load distribution may not achieve the desired balance.

Weighted Round Robin load balancing is often used in scenarios where server capacities differ, and administrators want to allocate traffic in a way that reflects those differences. It's particularly valuable in environments where hardware upgrades or changes are common, as weights can be adjusted to accommodate these modifications without needing to change the entire load balancing strategy.