Hi Dmitri, Kyle provides an excellent answer to your question (thanks Kyle!), but I will add just a bit more color as well. The ELB system has dependencies on AWS services (most notably EBS as Kyle mentions and as is described here in the post-mortem of one AWS' "cascading" outages: https://aws.amazon.com/message/680342/ ). If you use a vendor-neutral, instance-based load balancer (like HAProxy, Nginx, etc.) an outage of the EBS service will not affect your load balancing capabilities. And if you ever decide that you want to move your infrastructure to another provider, a software load balancer can move with you, while an ELB cannot.