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On Mon, Nov 24, 2003 at 04:29:54PM +0100,
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Date: Mon, 24 Nov 2003 10:29:50 -0500
From: "Ben M. Wall" <bmwall@xxxxxxxxxxxxx>
To: lvs-users@xxxxxxxxxxxxxxxxxxxxxx
Subject: Re: lvs-users Digest, Vol 10, Issue 35
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> Benjamin Wall wrote:
>
> > The loadbalancing is working on the 2 webservers, I have not set it up
> > on the database servers yet because of concerns about database
> > connection state and how LVS handles that (or doesn't).
>
> The single writer, many reader problem has not been solved in
> the general sense for distributed computing. It's difficult.
> LVS can't do it, databases (unless you're willing to shell
> out lots of money) don't do it easily. In these situations,
> something has to pass the write to all machines.
I am not trying to loadbalance across the databases. I just want failover
from one database to the other if the first database fails. My databases
(MySQL) are set up to replicate one another so that in the failover situation
the backup database will be mostly up to date.
>
> > What I want:
> >
> > Two Virtual servers (Direct Routing):
> > - 1 for http/apache (loadbalanced) (2 machines, more later)
> > - 1 for MySQL (simple failover) (2 machines)
> > Automatic addition/removal from LVS when failure detected
> > Director Failover (I have two machines for director duty)
> >
> > What I am confused about:
>
> To a newbie it is confusing. I've been on this project for 5yrs or so
> now, and I have a hard time keeping track of LVS and everything
> that hangs off it.
Well, that makes me feel better, for a moment there I though that I was the
only one who found this confusing! :)
>
> there are several software packages with similar functionality.
> Any of them will do the job. Mon was used initially, but
> no-one seems to be using it now. The maintainers of the other
> packages are all on this mailing list and can answer questions.
> You're going to have to figure out which one you want to use
> and then start installing. I know figuring it out is a bit
> of work, but that's what we have.
>
> > Director failover:
> > - I am planning on setting up heartbeat via serial cable.
> > - Which tool should I use for the takeover? vrrpd, Fake
> > - ldirectord, keepalived ??? or just mon, hearbeat, fake?
> > - Do I need connection table synchronization?
> > http://marc.theaimsgroup.com/?l=linux-virtual-server&m=105459391703228&w=2
>
> we didn't have the sync demon till relatively recently. If you don't mind
> users
> loosing connection on a failure, you don't need any of this.
> If you're providing state of the art service, then you need everything.
> I would get things going in stages, not to overwhelm yourself.
>
> Are the databases contacted via the webservers, or is the user's
> connection to the databases separate to the webservers? You
> will have to figure out the single writer, many reader
> problem for the databases first, then figure out failover
> for the realservers, then failover for the directors.
>
The databases are accessed only by the webservers. Again I dont think I need
to figure that one out. I only need to write to one database and the others
replicate that information.
> > - iproute2's advantage over eth0:10 style (is it just an iptables
> > issue?) ( I know next to nothing about iproute2 )
>
> as of 2.4 kernels, any new networking functionality requires the
> iproute2 style of setting up nics. iptables knows nothing about eth0:10
> style aliases. As long as you only have one IP on a NIC you don't need
> iproute2.
Wow I have been using 2.4 kernels for a while now, its a wonder that I never
ran into this before. So it seems like this is really a firewalling issue. It
seems to me like I would want to be able to use netfilter for each virtual
server seperately, and not just for the whole machine. Is iproute2 as easy to
set up as the eth0:185 syntax?
Thanks for everythng.
Ben Wall
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