RE: Re: O2 Hoster down ?

["Ian Willoughby" <ian@xxxxxxx>]

Having TTL's set low is a bit hacky (but not too much). Surely an
independent load balanced DNS is better way of doing this with bias
towards the primary. Load balanced DNS solutions usually (but not
always) have the ability to detect host availability when deciding which
host to route traffic to.

My 2p's worth :-)

R's
Ian


-----Original Message-----
From: Tony Lucas [mailto:tony@xxxxxxx]
Sent: 09 May 2003 10:26
To: 'ukha_d@xxxxxxx'
Subject: RE: [ukha_d] Re: O2 Hoster down ?

> -----Original Message-----
> From: Gerard McGovern [mailto:stuff@xxxxxxx]
> Sent: 09 May 2003 09:33
> To: ukha_d@xxxxxxx
> Subject: RE: [ukha_d] Re: O2 Hoster down ?
>
>
> > Unless you're a Tier1 ISP then you'll still be suscpetible to
> > backbone problems from your provider. If you can *guarantee*
> > 100% uptime for $200 a month backed up by SLAs ;) - I think
> > you could sell to a fair few corporates who currently pay
> > more for less.
>
> Well the company used for hosting is http://www.communitech.net/, who
> are now part of Interland (who are god damn huge). From memory their
> network has connections out via multiple Tier1 ISPs, hence the reason
> for the high availability.
>
> If you had a server from Communitech and another one from
> let's say One
> and One in the UK, I think it would be possible, with a budget of less
> than $250 per month, to ensure total 100% availability.
>

Hi Gerard,

With all due respect, its not that simple.

Having 2 servers in independant data centres is a long way towards
getting a great deal of redundancy, (especially with e-mail and dns),
but it wont give you 100%, for example:

Server 1 (At Communitech for example): Primary Mail Server, Also Handles
POP3 accounts for people, hosts some websites and does secondary dns

Server 2 (At OneandOne for example): Secondary Mail Server, works as a
backup for Server 1, doesnt handle pop3 accounts though, it also hosts
some websites, and does primary dns for the domains.


If Server 1 goes down:

The DNS would still work (it would run soley from Server 2 for that
time)
The e-mail would be held on Server 2, but not delivered until Server 1
came back online, nor could pop3 accounts be picked up from.
The websites on Server 1 wouldnt work.

If Server 2 goes down:

E-mail and pop3 etc would all still work correctly, as they would be
unaffected, and dns would continue to run but from one server, again
though, the websites would be offline on Server 2.

You could potentially avoid this by using very low TTL's on the zone
files for the domains and switching them when one machine falls offline,
and duplicating the files across the servers, but its a bit of a hacky
solution.

We tend to provide solutions like that for customers, who will mirror a
site across 2 machines, with dns etc running independantly (by us), so
worst case scenario things can be brought online much easier.

Also, as long as you have a reasonably reliable network (eg a BGP4
multihomed one with no single points of failure), any downtime should be
relatively insignificant, so in some cases having the machines together
could be benefical (Eg, one machine could take over the other's ip and
thus avoid website downtime, plus which synchronising sites could be a
lot easier over a LAN)

I know I've whittered on a bit here, but just thought I'd put my point
of view across, it's not a flame or anything remotely hostile towards
your opinions :o)

Regards,

Tony Lucas
Chief Executive Officer
XCalibre Communications Ltd
<http://www.xcalibre.co.uk>


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