I found this in the official ELB documentation
By default, a load balancer routes each request independently to the application instance with the smallest load.
but an article on Newvem says that ELB supports only Round Robin algorithm
Algorithms supported by Amazon ELB - Currently Amazon ELB only supports Round Robin (RR) and Session Sticky Algorithms.
So which one is it?
[1] http://docs.aws.amazon.com/ElasticLoadBalancing/latest/DeveloperGuide/US_StickySessions.html