takes 4 ENV variables to config:
CONSUL_URL=10.0.0.113:8500 - the ip and port of the consul server (or consul load balancer)
SERVICE=postfix-test - the service is the shortest possible version of the image of the containers that we want to grab ports for and load balance.
HA_MODE=tcp - see haproxy docs for node options... unless you are doing http.. you should stick to tcp
HA_PORT=25 - the port to listen on
you should also add an alias so you don't have to figure out what ip is the active server.
docker/mm/lb.docker-compose.yml for examples