What is a load balancer and why is it used in system design?

What is a load balancer and why is it used in system design?

• A. A load balancer distributes incoming traffic across multiple servers to improve availability, fault tolerance, and scalability.
• B. A load balancer caches data to speed up reads.
• C. A load balancer assigns IP addresses to new servers.
• D. A load balancer handles database sharding.

Answer: (D)

Distributing incoming requests across a pool of servers is the core idea. A load balancer sits in front of multiple servers and directs each new request to one of them. This spreads the workload so no single server becomes a bottleneck, and it provides fault tolerance because if one server fails, others continue handling traffic. It also makes scaling easier—you can add more servers to handle higher demand without downtime. Health checks keep the pool healthy by removing non-responsive servers from rotation, and routing decisions can use options like round-robin or least-loaded to optimize performance. Caching data to speed up reads, assigning IPs to new servers, and database sharding serve different purposes and aren’t the load balancer’s primary role. Caching speeds data access, IP assignment is handled by network/orchestration layers, and sharding partitions data across databases, often requiring a separate proxy or routing layer for database access.

Distributing incoming requests across a pool of servers is the core idea. A load balancer sits in front of multiple servers and directs each new request to one of them. This spreads the workload so no single server becomes a bottleneck, and it provides fault tolerance because if one server fails, others continue handling traffic. It also makes scaling easier—you can add more servers to handle higher demand without downtime. Health checks keep the pool healthy by removing non-responsive servers from rotation, and routing decisions can use options like round-robin or least-loaded to optimize performance.

Caching data to speed up reads, assigning IPs to new servers, and database sharding serve different purposes and aren’t the load balancer’s primary role. Caching speeds data access, IP assignment is handled by network/orchestration layers, and sharding partitions data across databases, often requiring a separate proxy or routing layer for database access.