FreeBSD: Disaster-tolerant fallover(?) Server switching software for FreeBSD / Linux?

Sam Smith S at
Tue Oct 16 20:03:19 BST 2001

On Tue, 16 Oct 2001, L. Cranswick wrote:
> For getting a server system (Web, FTP and Rsync) going where there
> is a physically separate redundant "fallover" server -
>   Is there software available that will detect if the primary
>   server has gone down (or failing) and auto-switch the
>   secondary server to take over transparently.
>   I guess this would also involve software on the DNS server as well
>   to redefine IP addresses and aliases?
> Any clues or links to intelligent ways of doing this with FreeBSD/Linux.
> (network group here is primarily composed of Linux fans at the moment)

What you need is two machines with multiple network cards.

Boxes A (the main one) and B (the backup) have one network card with
the same IP address assigned (they have other interfaces for admin
purposes, but the IP for www and user swervices is the shared one) , one
of which is configured to be administratively down at any one point (box
B as it's the backup). Box B then keeps watching for Box A to go pear
shaped, at which point it turns off the power to box A, brings the
network card on the "shared" IP address administratively up, logs into
the router and gets it to flush it's arp cache.

How long it takes between box A facing plant and box B coming up depends
on how often you check the box is in fact up.

As for actually doing it, a simple perl script should suffice.

Changing DNS is not a good way to do this as you don't know where the
old DNS entries will be cached.


  Failure: When Your Best Just Isn't Good Enough

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