IP address affinity is another popular way to do load balancing. In this approach, the client IP address is associated with a server node. All requests from a client IP address are served by one server node.
This approach can be really easy to implement since the IP address is always available in an HTTP request header and no additional settings need to be performed.
This type of load balancing can be useful if your clients are likely to have disabled cookies.
However, there is a downside to this approach. If any of your users are behind a NATed IP address then all of them will end up using the same server node. This may cause an uneven load on your server nodes.
NATed IP address is really common, in fact, anytime you are browsing from an office network its likely that you and all your coworkers are using same NATed IP address