[plug] IP Alias/Arp dilemma...

[Trevor Phillips]

Mike Holland wrote:
> 
> Sorry I cant answer your question, but am curious why you took this
> approach. Wouldnt it be easier to use DNS name aliases for this? That
> seems to be the normal way. You could set a short time for caching.

We used to do it via DNS, but that's pretty useless in a Disaster Recovery
scenario, where you instantly want one machine to stop being The One, and
another machine to start being it, due to the delay in DNS changes percolating
out. And since this is primarily a public Webserver, it's pretty important that
it's accessible from the whole world.

The IP Alias solution is a lot nicer, as well as giving us, the server admins,
control over it. It means a swapover involves just downing one Net Interface,
and upping another (with some possible service restarts). It also means that it
can be done automagically by Watchdog scripts if need be.

DNS change, as well as the delay, involves negotiating with the Comms guys to
change DNS entries, which itself involves a delay.

This Arp Cache issue is the first hurdle we've hit. And as I mentioned, the old
Solaris boxes didn't have it, as they had outgoing traffic on the new Alias,
which updated the Arp entries.

-- 
. Trevor Phillips             -           http://jurai.murdoch.edu.au/ . 
: CWIS Systems Administrator     -           T.Phillips at murdoch.edu.au : 
| IT Services                       -               Murdoch University | 
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