[ILUG] DNS based failover for ftp servers?

[Jeroen Massar]

Conor Daly wrote:
> Hi all,
> 
> This is an area where I basically have no clue.  I have an RHEL box that
> runs an ftp server to receive incoming files.  I don't necessarily have
> control of the upstream suppliers so I need to have something there at all
> times to catch incoming files.
> 
> A recent failure hung the machine to the point where an ftp connection
> would hang waiting for a response.  The machine would respond to pings.  I
> took the machine down for repairs and booted another to receive the
> incoming ftp files.  I just gave it the primary machine's ip address.

Instead of thinking about abusing DNS for this, I propose that you use
VRRP: http://en.wikipedia.org/wiki/VRRP

Which nicely links to http://sourceforge.net/projects/vrrpd/

VRRP in short handles the case where one machine doesn't respond to an
IP address, then the one of the others machines takes over. When it is
back it takes back over.

VRRP though requires support from your upstream.

If that is not available, you can always go to: http://www.linux-ha.org/
which uses a heartbeat tool (not the SixXS one ;) to signal "hi I am
still here" every n microseconds. When one of the pair notices that this
signal is not sent anymore, the other takes over the IP.


For an FTP setup, you can best use one of the above and then in addition
simply configure 2 IP addresses in DNS. Then when one of the boxes goes
down the other takes over the other boxes IP, but both IP addresses
remain available, resulting in no connect timeouts for the clients.
Users can still connect separately to both IP's. Of course if you have 3
addresses available. This 'shares' the load over both addresses but
still allows for high availability.

In DNS this officially could be accomplished with SRV records, that act
as a generic MX-alike record for everything, unfortunately there are
very few FTP implementations that actually use it, thus it is of no use
for your purposes.

Greets,
 Jeroen