[CentOS] Question about clustering

Thu Jun 19 00:12:30 UTC 2014
SilverTip257 <silvertip257 at gmail.com>

On Wed, Jun 18, 2014 at 2:46 PM, <m.roth at 5-cent.us> wrote:

> Digimer wrote:
> > On 18/06/14 12:32 PM, Alessandro Baggi wrote:
> >> Ok, fencing is a requirement for a cluster for hardware failure.
> >> I've  another question about this arg, but for software failure.
> >> Supposing to have a cluster of httpd installation on 6 virtualized
> >> hosts, each one on a different server. Suppose also that a guest (named
> >> host6) has a problem and can't start apache. With this scenario, the
> >> ipmi, ups are unnecessary. How to work fencing in this way? How to make
> >> fencing node?
> >>
> > I'm not sure I understand properly... You mean that you have 6 VMs which
> > are nodes in a cluster, or 6 nodes, each hosting a VM you want to make
> HA?
> <snip>
> I'm not clear on what you mean, either. Is this supposed to be a
> load-balancing cluster? If so, and you expect that kind of load, I,

My interpretation mirrors Mark's ... sounds like you want to load balance
between the six servers.
If so, you might create a proxy with haproxy [0] [1] that will relegate
connections to each of your six nodes.

[0] http://haproxy.1wt.eu/download/1.4/doc/configuration.txt
[1] http://www.rackspace.com/knowledge_center/article/setting-up-haproxy

> personally, would *never* put a VM on them - I'd want the full resources
> of the o/s brought to bear on that load, and use multiple real hardware

Makes sense in the terms of hardware redundancy, but if it's OS level
redundancy then this could fly.  _BUT_ it isn't as ideal as having separate
hardware.  If Alessandro's VMs are clustered between a pair of nodes with
shared/replicated storage, then I'd say it is a realistic scenario.
 Layered redundancy for the win!  (akin to layered security)

Rackspace has haproxy as part of their cloud offerings [2].
Albeit likely resources not on the same single piece of hardware!

> for the other members. Doing this with VMs is only multi-threading the
> load, and adding more, with all the context switches.
>      mark
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//  SilverTip257  //