alt Hacker NewsBecause unless your TTL is exceptionally long you will almost always have a sufficient supply of new users to balance. Basically you almost never need to move old users to a new target for balancing reasons. The natural churn of users over time is sufficient to deal with that.
Failover is different and more of a concern, especially if the client doesn't respect multiple returned IPs.
I'm assuming OP means cloud-based load balancers (listening on public ips). Some providers scale load balancers pretty often depending on traffic which can result in a set of new IPs.