Comment by procaryote
5 hours ago
You hash the servers because then adding or removing a server doesn't directly affect other servers position on the ring; adding a server just takes some load from som servers.
This is useful because you want stickiness, so requests for the same key mostly go to the same server.
Sorting servers by weight means that removing or adding a server will shift a lot of traffic from the servers it used to go to. A flapping server early in the list will break stickiness for the whole set of servers.
The simplicity of stable hashing means you don't have to think about new sets, old sets, table rebuilds, synchronisation schemes etc, and that's useful because every such extra step adds bugs and corner cases
Ah, right. The joys of being a fool in public.
The part I missed is that the load balancers don't have a consistent view of the set of servers. There is no magical synchronization scheme that creates that consistent view. You want load balancers with slightly different ideas of what servers are available to mostly make the same choices for the servers they do agree on.
Doh! I should have been able to infer that from the original solution.