upstream AAA
{
  server server1 fail=0;
  server server2 backup;
} 

www0 IN A 1.2.3.1 
www1 IN A 1.2.3.2 
www2 IN A 1.2.3.3 
www3 IN A 1.2.3.4 
www4 IN A 1.2.3.5 
www5 IN A 1.2.3.6 

www IN CNAME www0.domain.com. 
IN CNAME www1.domain.com. 
IN CNAME www2.domain.com. 
IN CNAME www3.domain.com. 
IN CNAME www4.domain.com. 
IN CNAME www5.domain.com. 
IN CNAME www6.domain.com. 

# dig mail.ru

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.30.rc1.el6_6.2 <<>> mail.ru
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34477
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 2, ADDITIONAL: 4

;; QUESTION SECTION:
;mail.ru.                       IN      A

;; ANSWER SECTION:
mail.ru.                60      IN      A       94.100.180.200
mail.ru.                60      IN      A       217.69.139.200
mail.ru.                60      IN      A       94.100.180.202
mail.ru.                60      IN      A       217.69.139.202

;; AUTHORITY SECTION:
mail.ru.                447     IN      NS      ns1.mail.ru.
mail.ru.                447     IN      NS      ns2.mail.ru.

;; ADDITIONAL SECTION:
ns2.mail.ru.            30      IN      A       94.100.180.138
ns2.mail.ru.            30      IN      AAAA    2a00:1148:db00::1
ns1.mail.ru.            30      IN      A       217.69.139.112
ns1.mail.ru.            30      IN      AAAA    2a00:1148:db00::2

;; Query time: 27 msec
;; SERVER: 78.108.87.253#53(78.108.87.253)
;; WHEN: Tue May 19 21:31:34 2015
;; MSG SIZE  rcvd: 213