Hi just like to share, I have some issue before that when I shutdown master or slave dns server all my site is no longer accessible, So I try to read the options for resolv.conf and found this options "options attempts:1 timeout:1 rotate"
search yourdomainname or subdomainname
nameserver xxx.xxx.xxx.xxx # ip addrress of your ns1
nameserver xxx.xxx.xxx.xxx # ip address of your ns2
options attempts:1 timeout:1 rotate # add this at the end of the line
Add options to all your server (www, images... etc) What does this do? If master dns shutdown it will used your ns2 as your name service. So you'll prevent server un accessable. Same with slave shutdown it will used ns1 for name service of all your server.
I hope this help... cause it take me time to resolve my issue on this.