HA LAMP

[Thomas Champagne]

On 4/10/07, Joseph Mack NA3T <jmack at wm7d.net> wrote:
> On Tue, 10 Apr 2007, Thomas Champagne wrote:
>
> > Hi
> > I would like to create a high availability LAMP. But I have only two
> > machines.
>
> that's plenty
>
> > There are two services on each servers : Apache and Mysql.
> > Each service have its IP and have a VIP address :
>
> > The problem : Accessing services from a remote client
> > (outside the cluster) to the VIP is ok. But when the
> > client is the cluster, it always connects on the local
> > machine.
> >
> > For example, when Apache connects to the VIP Mysql with
> > PHP script, it always connect to the local Mysql. So if
> > Mysql is down on the local but up on the other, Apache
> > can't connect to Mysql.
>
> people coming to this mailing list are always trying to
> balance the 3rd-tier (in your case, mysql). If this was easy
> to do, that would be one thing, but with the current design
> of LVS, it's next to impossible.
>
> I continue to point out (to no avail apparently) that the
> first connection (here to apache) is balanced, so that the
> connection to the 3rd-tier (here to mysql) will be (at least
> reasonably) balanced. So you have the balanced apache on
> your realserver connect to the local mysql.
>
> To have a valid realserver, both apache and mysql have to be
> up. Maybe people think then that there's twice the chance of
> the realserver going down and for the same hardware their
> 99% uptime realserver is now a 98% uptime realserver. So
> they have to be prepared for apache_1 to connect to mysql_2.
> That would be true if the only failures on the machine were
> the demons dying and that they died independantly. I don't
> run a production internet site, so I don't have any numbers
> on failures in those situations, but it's not often that
> demons for no reason at all just die or stop answering. Most
> failures seem to be disks and fans dying, memory chips going
> bad resulting in corrupt files being written, loss of
> network connectivity to the outside world (the backhoe
> problem) and surprisingly routers dying. Rarely does the
> demon die. In which case requiring two demons to have a
> functioning realserver may not change the downtime a whole
> lot. There's many other demons running on the realserver
> which are part of unix, and which are required for a running
> machine, so you actually need maybe 10-20 demons for a
> functioning realserver, in which case an extra one (mysql)
> isn't going to make a whole lot of difference.
>
> But let's say a functional realserver will have twice the
> downtime because it requires two functioning realservsers.
> Well that's high availability life when you have a service
> that requires multiple demons. You have to fail out the
> realserver when either service goes down. That's all.
>
> Last exchange I had on this subject, the person didn't have
> any technical reason why they needed to balance the
> 3rd-tier. They just wanted it. So I haven't been convinced
> that you must have a balanced 3rd tier.
>
Ok, I agree.

> > This command returns nothing :
> > ls /lib/modules/2.6.18-4-686/kernel/net/ipv4/netfilter/ | grep ROUTE
> >
> > So, I can't use the target ROUTE.
>
> sure you can. Just use google to find it.
>
I have googled before posting but I didn't find anything. I'm not very
good with iptables and iproute2.
I'd just like to know, for my personnal knowledge.
Thanks

> Joe
>
> --
> Joseph Mack NA3T EME(B,D), FM05lw North Carolina
> jmack (at) wm7d (dot) net - azimuthal equidistant map
> generator at http://www.wm7d.net/azproj.shtml
> Homepage http://www.austintek.com/ It's GNU/Linux!
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