Re: [cobalt-users] Setting a Seconday DNS Server - Help Please

["Hostmaster : Beyond2K" <Hostmaster@xxxxxxxxxxxxxx>]

> > Original query from Multivex:
> >
> > I want to prevent downtime in the case of a hard disk failure in my RAQ or
> > in case DNS problems arise.<<
> >
> > I have two RAQs, each on a different location. I would like to use the
> > second to mirror the first, having both >actualized content. So in case one
>>  fails, being the other the secondary DNS for the domain, it could take over
> > and continue serving.<<

> We have been doing this for around 3 years, more recently with 3 x RAQ's..
> will ask our webmaster if we can post the technical info Monday next week.

I can only continue and give the details of how the servers are setup.

I will warn you that this solution is far from orthodox and involves using a complete set of DNS records and websites per box. I
would not recommend our identical setup to anyone hosting third part websites.

1) Make sure you have the 2 nameservers authoritive for your domains, the IP's are correct and on seperate boxes.

2) DNS - Allocate primary/master nameserver to your most stable server in all SOA records and network settings on both boxes. Set
the TTL in all SOA records to a low timeframe (we use 3600 - 1 hour - this will increase your DNS traffic). Setup complete DNS
records on both boxes - pointing to IP's on the same box only.

3) Setup websites etc on each box as per the IP's used for your DNS records.

What we see:

A split of traffic between the servers depending on which nameserver is used by the users ISP for the domain lookup. This is a
downside as all traffic (web, email, ftp, etc) is split between boxes. Changes made to any sites or settings have to be down on both
boxes individually. Email has to be picked up from both boxes. You could in DNS setup records which point to just one email server
to prevent this but would have to wait for the server to come back up before email could be retrieved.

What happens when things go wrong:

a) Upon server failure: the ISP cannot query a particular nameserver and sends traffic to the other.

b) Upon bind / named / DNS failure: the ISP cannot locate a particular nameserver and sends traffic to the other.

c) Upon apache, sendmail, pop, imap failure but bind still working: Shutoff DNS as soon as paged with the failure then ISP's cannot
locate a particular nameserver and sends traffic to the other. I am working on a script which checks service availability and shuts
down bind automatically upon service failure to save me getting out of bed :)

Conclusion:

You basically have 2 boxes setup identically except for the DNS records which differ between each box as they point to local box
IP's only. You can use rsync or similar to duplicate website content from one box to another. We actually run 3 servers with the
third setup uniquely as above and listed as an additional nameserver. This system "does" work as long as you can make the nameserver
running (bind) on the failing box unavailable. A complicated, unorthodox and far from elegant system I'm sure you'd all agree but a
working one.

If you need any further help with this please contact me on or off list.

Brett
Beyond2K - Webmaster / Hostmaster
---------------------------------------------
The World's premier mobile phone boutique
With free SMS & free personal No's
www.b2kcomms.co.uk