Load Balancing Algorithms

Round Robin (Default)

Requests are distributed equally among all servers:

upstream backend {
    server s1:8080;
    server s2:8080;
    server s3:8080;
}

Flow: S1 → S2 → S3 → S1 → S2 → ...

Best for: Servers with equal capacity

Least Connections

Route to the server with fewest active connections:

upstream backend {
    least_conn;
    server s1:8080;
    server s2:8080;
}

Best for: Long-lived connections (WebSocket, SSH)

IP Hash

Same client IP always routes to same server:

upstream backend {
    ip_hash;
    server s1:8080;
    server s2:8080;
}

Best for: Session persistence without shared storage

Hash on Variable

Hash based on any Nginx variable:

upstream backend {
    hash $cookie_userid;
    server s1:8080;
    server s2:8080;
}

Choose your method!