Round Robin: Requests go to servers in order. Server , , , , , . Simple but ignores server capacity.
Weighted Round Robin: Servers get requests proportional to their weight. A server with weight gets x the requests of weight .
Least Connections: Send to the server with fewest active connections. Good when request processing time varies.
IP Hash: Hash the client IP to pick a server. Same client always goes to same server. Useful for session affinity.
Random: Pick a server randomly. Surprisingly effective at scale.