[OPEN-ILS-DEV] Clustering Mechanics

[Uhlman, Brandon EDUC:EX]

Hi, everyone.

British Columbia is well into the planning stages of a pilot Evergreen
implementation for some of our libraries. Right now, our goal is to
enter production with the first participating sites this fall. After a
meeting yesterday, one of the participants asked me about load balancing
and the brick structure (that PINES is using) that I couldn't answer
with complete confidence.

He asked: "...it seems there are two levels of load balancing. First,
LVM is used to load balance between identical units of brics. Second,
within a bric, balance is based on application. I wonder if a single
level of load/function balance can be used to reduce number of servers
and achieve similar levels of performance and redundancy."

My understanding, sketchy at best, is that the Jabber/OpenSRF router
machines on each of the bricks still have to do some (relatively)
processor-intensive work, making their max workload CPU-bound.

Therefore, using only OpenSRF/Jabber routing as sort of an ad hoc load
balancer between an arbitrary number of app servers - think of it as a
single brick, containing all the application machines - is limited by
how much processor work the routing box needs to do. I think this played
itself out Georgia's own implementation as well, when deciding how big
to make the individual bricks.

Another option, if I understand the process correctly, would be to run
an LVS-type load balancer that distributes incoming requests directly to
an arbitrary app server, based on whatever LVS algorithm is being used,
and that app server deals with all the requests thrown at it, bypassing
this Jabber/OpenSRF router idea. This feels like a Stephen Colbert
situation to me - I *feel* like this is a bad solution in my gut, but I
can't quite put my finger on why. :-)

If anyone who has looked at the codebase or considered the clustering
mechanics more than I has any thoughts on this, that'd be super.

Cheers,

Brandon

================================
Brandon W. Uhlman
Systems Consultant
Public Library Services Branch
British Columbia Ministry of Education

605 Robson Street,  5th Floor
Vancouver, British Columbia
V6B 5J3

Phone: (604) 660-2972
Toll-free: (800) 663-2165

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