[joosters]

It's surprising that "least requests" is still so less commonly used than random or round-robin. It's a simple metric and yet it handles work-sharing remarkably well, without any need for servers to communicate their load back to the LB. (As you correctly say, the LB needs to be aware of idle/keep-alive connections in order to balance properly)

[Also, to be pedantic, it should really be called "fewest requests" - but I've never seen a product call it that!]