Strowger is the Flynn HTTP/TCP cluster router. It relies on service discovery to keep track of what backends are up and acts as a standard reverse proxy with random load balancing. HTTP domains and TCP ports are provisioned via RPC. Only two pieces of data are required: the domain name and the service name. etcd is used for persistence so that all instances of strowger get the same configuration.
The primary benefits are that it uses service discovery natively and supports dynamic configuration. Both HAProxy and nginx require a new process to be spawned to change the majority of their configuration.
Since this is very much an alpha prototype, a service discovery shim for HAProxy would make more sense for production currently.