Load Balancing Algorithms

First of all, the load balancer has to keep track of which servers are healthy by routinely pinging them and recording if they respond. If a server fails a health check, it is removed from the viable server list, and will only be added again if it passes a later health check.

Algorithms

Least Connection Method

LB directs traffic to the server with the fewest active connections

Least Response Time Method

LB directs traffic to the server with the fewest active connections and the lowest average response time.

Least Bandwidth Method

LB directs traffic to the server currently serving the least amount of traffic, measured in Mbps (megabits per second).

Round Robin Method

LB cycles through a list of servers and sends each new request to the next server.

Weighted Round Robin Method

Weight servers based on their processing capacities. Higher weighted servers are attempted first.

IP Hash

LB calculates hash of the client IP address, and uses that hash to determine which server will receive the traffic.

Software

In addition to open source load balancers like HAProxy, there are costly hardware load balancers like NetScaler that are highly effective.