load balanced configuration

[Matt Iavarone]

I think the original question was around stateless load balancing, not
clustering.  Cross DC clustering is a headache, but HA web sites aren't
exactly terchnical challenges these days.

On May 19, 2010 4:33 PM, "Alex Dean" <alex at crackpot.org> wrote:


On May 19, 2010, at 2:47 PM, keith smith wrote:

>
>
> Hi Plug,
>
> I am considering combining the ...
You're entering a world of pain. :)

HA is cool, but is no panacea.  If you haven't actually experienced downtime
due to your server crashing or your datacenter losing connectivity, I
recommend thinking long and hard about it.  Don't solve a problem you don't
have.  The downtime created from unneeded failovers will likely exceed the
actual/real downtime caused by either a server or datacenter being offline.
 Managing the cluster itself (as distinct from the services provided by the
cluster) needs to be accounted for as an expense/responsibility.

I don't want to sound overly pessimistic.  I've set up quite a few HA
clusters, and actually enjoy it most of the time.  But it WILL cause you
headaches in the middle of the night which you wouldn't have had if you only
had a single server.

Leave yourself lots of time to set up a development/test cluster, and abuse
it in many ways.  Pull out network cables, kill the switch, yank out power
cables, etc.  Do this with real hardware, not VMs.

When the cluster nodes lose contact with each other, both will decide to
become primary.  This is a split brain.  This can happen when the switch
in-between them gets busy and starts dropping pings.  Now, you can always
recover from such things.  I'm just recommending you become very familiar
with these issues before going live with this setup.

http://clusterlabs.org/wiki/Main_Page
http://people.linbit.com/~florian/heartbeat-users-guide/

Let me/us know if you have specific questions once you start setting things
up.  Good luck!

alex
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