One Server, two IPs, DNS setup

[Joseph S D Yao]

On Mon, Sep 25, 2006 at 07:11:53PM -0700, Tomas Narvaez wrote:
> Joe:
> 
> Thank you for your answer. 
> What solution do you propose for high availability?
> 
> Regards,
> 
> Tomas


It depends on how much money you have.  One answer is something like
F5 Network's BigIP/3DNS solution.  If you don't have lots of money, it
still depends on how you're configured.  Here are some possibilities:

- Two Web servers with different IP addresses.  Each one, when booted,
  uses some mechanism to try to claim a shared virtual IP address.  Use
  'wget' or the like to synchronise the content.  Use only the virtual
  IP address as the Web site's IP address.

- Two synchronised Web servers with different IP addresses.  One is
  entered into DNS as the Web site's IP address, with a low TTL (if you
  think failure likely).  An out-of-band mechanism monitors the Web
  site's availability.  If it goes down, the OOB mechanism changes the
  DNS to use the other IP address.  And back.

- Two synchronised Web servers with different IP addresses and a shared
  virtual IP address, on different networks with different AS numbers.
  As long as one remains up, that one's AS advertises the virtual IP
  address/network.  When it fails, the other AS advertises it.

- Two synchronised Web servers with different IP addresses.  Each has a
  link to the other, saying: "This is a redundant mirror of this site.
  Please bookmark it in case this one goes down."

You trade off money with SOMEBODY's extra effort.  ;-)


[NOTE: 3DNS is now called Global Traffic Manager (GTM), but I still need
to look that up.]


-- 
Joe Yao
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