[Pacemaker] Help with N+1 configuration

[Cal Heldenbrand]

Thanks for the info Phil!  I'm going to play around with my configs with
what you've recommended... but a few questions below:

can be started in any order. You don't need to specify any location
> constraints to say where memcache can run, or to keep the memcache
> instances from running multiple times on one node. The clone handles all of
> that.
>

That seems very handy -- and I don't need to specify 3 clones?   Once my
memcached OCF script reports a downed service, one of them will
automatically transition to the current failover node?



>
> 2) have ip1 on a node with a working memcache
>
> primitive ip1 ...
> colocation ip1_on_memcache inf: ip1 memcache_clone
>

Is there any reason you specified just a single memcache_clone, instead of
both the memcache primitive and memcached_clone?  I might not be
understanding exactly how a clone works.  Is it like... maybe a "symbolic
link" to a primitive, with the ability to specify different metadata and
parameters?


>
> I've chosen a score of -10000 for ip2_not_on_ip1 because I assume you
> could, if you had no other choice, run both IPs on one node.


Yes, that's a super awesome functionality.  Despite the advertisement of
consistent hashing with memcache clients, I've found that they still have
long timeouts waiting on connecting to an IP.  So, keeping the clustered
IPs up at all times is more important than having a seasoned cache behind
them.


>
> 4) you have some preferences about which servers are active in a
> non-failure situation
>
> location ip1_on_mem1 ip1 mem1: 100
> location ip2_on_mem2 ip2 mem2: 100
>

I think I've had the wrong mentality with trying to *force* a mem1 and mem2
to their corresponding clustered IP addresses.  The reality is, all I need
are two IP addresses, with (hopefully) two separate instances of memcached
running on them.  In the future I might expand to more servers, but for now
I think your proposed method will work great.

Thanks again for your advice!  I'll probably ping back with more annoying
questions if that's okay.  :-)

--Cal
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