How to use DNS name backends in haproxy

haproxy_resolvers.cfg

global
    log 127.0.0.1 local2
    pidfile /var/run/haproxy.pid
    user haproxy
    group haproxy
    maxconn 1000

defaults
    log global
    mode http
    option httplog
    option dontlognull
    timeout connect 50000ms
    timeout client  50000ms
    timeout server  50000ms


resolvers dns
 nameserver dns-0 10.255.255.131:53
 nameserver dns-1 10.255.255.132:53


frontend api
 bind *:9000
 bind *:443
 mode tcp
 option tcplog
 default_backend api-backend

backend api-backend
 balance roundrobin
 mode tcp
 server site-1 api1.com.au:443 resolvers dns check verify none inter 1000
 server site-2 api2.com.au:443 resolvers dns check verify none inter 1000