Load balancing distributes traffic across multiple servers to improve reliability and performance.
Load balancing distributes incoming traffic across multiple servers to prevent any single server from becoming overwhelmed. Instead of all requests hitting one server, they spread evenly across many servers.
Think of it like multiple checkout counters at a store. Instead of one cashier handling all customers (slow, overwhelmed), you have several cashiers sharing the load (fast, efficient).
Single Server: Works fine for small traffic. But when traffic spikes - product launch, viral post, sale event - the server crashes. Users see error pages.
Load Balancer: Sits in front of multiple servers. Distributes traffic evenly. One server crashes? Load balancer routes traffic to healthy servers. Users never notice.
The user has no idea multiple servers exist - they just get a fast response.
Round Robin: Send requests to servers in order. Server 1, Server 2, Server 3, back to Server 1. Simple and fair.
Least Connections: Send to the server currently handling the fewest requests. Good when requests take different amounts of time.
IP Hash: Same user always goes to same server. Useful when sessions are stored on specific servers.
Learn how your application intelligently routes requests to the right database shard without users ever knowing.
Weighted: Send more traffic to powerful servers, less to weaker ones.
Amazon during Prime Day: Millions of people shopping simultaneously. Load balancers distribute traffic across thousands of servers worldwide. No single server crashes.
Netflix: Millions streaming video at night. Load balancers route requests to the nearest, least-busy servers. Everyone streams smoothly.
Banking Apps: Handle millions of transactions daily. Load balancers ensure no server becomes a bottleneck.
Hardware Load Balancers: Physical devices. Expensive but powerful. Used by large enterprises.
Software Load Balancers: Programs like Nginx, HAProxy. Flexible, cheaper, easier to scale.
Cloud Load Balancers: AWS ELB, Google Cloud Load Balancing. Managed services, pay for what you use.
High Availability: One server fails? Others keep running. Users never see downtime.
Scalability: Need more capacity? Add more servers behind the load balancer.
Performance: Distribute load means faster response times for everyone.
Maintenance: Take servers offline for updates without affecting users.
Small apps on a single server do not need load balancing. As traffic grows, load balancing becomes essential.
If your server CPU hits 100% during traffic spikes, you need load balancing. If downtime costs money or users, you need load balancing.
Many apps start with a load balancer (even with one server) for future-proofing. As traffic grows, they add servers behind it. The architecture is ready to scale.
Load balancing is fundamental to modern web infrastructure. Almost every major website uses it. Understanding how it works helps you build scalable, reliable applications.
