A load balancer acts as the "traffic cop" sitting in front of your servers and routing client requests across all servers capable of fulfilling those requests in a manner that maximizes speed and capacity utilization and ensures that no one server is overworked, which could degrade performance.
Load balancers are critical for high availability and horizontal scaling. They allow backend services to be added or removed dynamically without disrupting the client, and provide health checking to ensure traffic is never sent to a failed node.
Load balancing is the entry point of our reliability strategy. We privilege Layer 7 (Application) load balancing over simple Layer 4 (Transport) distribution, allowing us to make intelligent routing decisions based on content, cookies, or headers. This enables advanced deployment strategies like Canary and Blue/Green.