Haproxy

Load balancers are invisible until they break. Then they’re the only thing anyone talks about. Here’s how to get them right. Algorithms That Matter Round Robin Requests go to each server in sequence: A, B, C, A, B, C… 1 2 3 4 5 upstream backend { server 10.0.0.1:8080; server 10.0.0.2:8080; server 10.0.0.3:8080; } Good for: Homogeneous servers, stateless apps Bad for: Servers with different capacities, long-running requests Weighted Round Robin Some servers get more traffic: ...

Round robin is the default. It’s also often wrong. Here’s how to choose load balancing strategies that actually match your workload. The Strategies Round Robin Each request goes to the next server in rotation. 1 2 3 4 5 upstream backend { server 10.0.0.1; server 10.0.0.2; server 10.0.0.3; } Good for: Stateless services, similar server capacity Bad for: Long-running connections, mixed server specs, sticky sessions Weighted Round Robin Same rotation, but some servers get more traffic. ...

Not all load balancing algorithms are equal. The right choice depends on your traffic patterns, backend capabilities, and consistency requirements. Round Robin The default. Requests go to each server in turn. R R R R e e e e q q q q u u u u e e e e s s s s t t t t 1 2 3 4 → → → → S S S S e e e e r r r r v v v v e e e e r r r r A B C A Nginx: ...

Round robin is the default, but it’s rarely the best choice. Here’s when to use each algorithm and why. The Algorithms Round Robin 1 2 3 4 5 upstream backend { server 192.168.1.1:8080; server 192.168.1.2:8080; server 192.168.1.3:8080; } Requests go 1→2→3→1→2→3. Simple, fair, ignores server load. Use when: All servers are identical and requests are uniform. Problem: A slow server gets the same traffic as a fast one. Weighted Round Robin 1 2 3 4 5 upstream backend { server 192.168.1.1:8080 weight=5; server 192.168.1.2:8080 weight=3; server 192.168.1.3:8080 weight=2; } Server 1 gets 50%, server 2 gets 30%, server 3 gets 20%. ...