spinifex/docs/coverage/elbv2/intro.md

Two data planes

The data plane is a system-managed load balancer VM, launched automatically during CreateLoadBalancer. Application Load Balancers run HAProxy for the L7 surface — rules, fixed responses and redirects over HTTP and HTTPS. Network Load Balancers run nginx stream for the L4 surface — TCP, UDP, TLS and TCP_UDP — because HAProxy cannot load-balance UDP. The agent selects the engine from the configuration the control plane delivers, so the choice follows the load balancer type and is not separately configurable.