Avoiding Sinkholing in Load Balancing with Prequal

In this article, we explore the challenges of load balancing in non-trivial systems and introduce a new technique called Prequal to address these issues. Load balancing is essential to ensure that no single component becomes overwhelmed with requests, but it can be difficult to achieve when dealing with complex, distributed systems.
To understand why, imagine you’re at a crowded restaurant and want to evenly distribute your food orders among the servers. If you simply divide the orders by the number of servers, some servers may end up with too many orders and others with too few. This is similar to what happens in load balancing, where some components may become overloaded while others sit idle.
Prequal addresses this problem by focusing on a different metric: service level objectives (SLOs). SLOs are the minimum performance levels that a system must achieve to meet its goals. By defining SLOs for each component, Prequal can ensure that each component is loaded appropriately based on its capacity and workload.
Think of it like a buffet with different food stations. Each station has a specific menu item with a certain amount of food available. If too many people gather at one station, the others may run low on food. Prequal would ensure that each station has an appropriate number of people to avoid overloading any one station.
Prequal also considers the timing of requests and how they affect load balancing. Imagine a river with different water levels throughout the day. If you only check the water level once a day, you may not see changes in the river’s flow. Prequal takes into account these changing conditions by probing the system frequently to better understand its current state.
In summary, Prequal is a new technique for load balancing that focuses on service level objectives and frequent probing to ensure that each component is loaded appropriately based on its capacity and workload. By avoiding sinkholing and overloading, Prequal can help maintain a stable and efficient system, even in complex, distributed environments.