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David Carlson wrote:
We are putting a bid in on a fairly major web site. The client has asked
for 24/7/365 reliability.
We were initially going to bid a Linux virtual server direct routing
solution with main and backup Linux directors in a multihomed data
centre. http://www.linuxvirtualserver.org/VS-DRouting.html
We were proposing the following hardware:
Linux Director and Backup director to route the requests to Real servers
on the LAN
Real servers 1 & 2 to do the work and route data back to the user
DB server 1 to provide the data to the real servers.
However, our partner has come up with an interesting wrinkle. They have
a second data centre where they can host a mirror of our site. It uses a
different company for main internet service, so it is not only
geographically removed, but has different power and internet service
too.
We are now going back and revisiting out hardware configuration. It
would seem that with two physical locations, we should use IP tunneling.
http://www.linuxvirtualserver.org/VS-IPTunneling.html. In this case, our
hardware configuration would be
**At Main location**
Linux director
Real page server 1
DB Server 1
**At alternate location**
backup linux director?
Real page server 2
DB server 2?
We've never done this before. But if it works, it would sure increase
our claimed reliability as we can talk about multihomed, geographically
separate, entirely redundant systems.
My questions are - what do we do with the Linux Director at the main
site to have a failover solution. If the internet service to the main
site fails, how does the alternate site know to take over receiving
requests? Given that it is elsewhere on the WAN, how does the backup
site update local routers with the virtual IP? Do we need a backup Linux
director at the alternate site? What about if the main site Internet is
OK but the Main Linux director fails. Will a backup director at the
alternate site take over and still send requests to real server 1 at the
main site.
Anyone done anything like this before or have a better solution?
Thanks in advance.
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Not my area of expertise but wouldn't it be more logical to use the
second site as either complete failover using BGP routing (or possibly
active/active but then how the heck do you keep your databases partioned
/ in sync ?)
Why don't you make each site complete mirrors i.e.
Each site has :
Dual Internet Feeds
Dual Switch fabric (CISCO ?)
Dual Firewall (IPTABLES)
Dual Loadbalancer (LVS)
Dual Web Server (Preferably more than 2) (?)
Dual Database (1 for failover using log shipping) (?)
BGP routing at the ISP level will move your VIP to the other site as and
when required.
If you wanted to do active/active why would the other site need to know/
care whether the first site exists ?
Database sync would be your major obstacle..
This kind of thing always gets expensive... :-).
--
Regards,
Malcolm Turnbull.
Crocus.co.uk Ltd
01344 629629
http://www.crocus.co.uk/
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