Apache + MySQL solution for online tests!!

[Joseph Mack NA3T]

On Sat, 23 Dec 2006, Roshan Sumbaly wrote:

> Sir,
> I am new to this field of load balancing and would require some help. We
> have a PHP + MySQL based online exam software which conducts simple online
> exams (in the form of Multiple Choice Answers). The software uses MySQL
> backend and Apache web server. We had a mock test and realised that the
> minute the number of students logging in increased to beyond 30, the
> computer became slow and finally couldn't withstand it. Beyond 30 students
> sitting at once the PHP pages failed to load and students couldn't log in.
> Luckily this was the mock exam!!

I have not setup any software like this, but I'm suprised to 
hear of the poor response. I expect students are only 
clicking once a minute or so, requiring the computer to 
handle a click every 2 secs.

> We also heard about DNS Load Balancing. Will this help?*

One of the developers here proved this was worthless 10yrs 
(or more ago). Some commercial setups are using fast DNS, 
but then they control the DNS server.

> The issue* is we
> don't want a student's test answers to be stored in various computers. It
> should be that once a student connects to one server, he should be on that
> server itself.

yes. have a persistent https connection.

> (We don't mind replicating all the databases of
> Questions/Answers as well as students' info on all the server computers)
>
> If DNS load balancing is not the solution, then is LVS the right answer?

I don't know if it's the right answer, but it will do what 
you want.


> If
> yes, which LVS (we went through the site to find various versions of LVS
> (LVS- NAT or LVS-TUN or LVS-DR?).

It's like asking which is best, a Chevy or a Ford? They both 
get you to work and let you do your shopping. Set up a 
simple (2 realservers, 1 director) LVS-NAT, and an LVS-DR 
using the instructions in the mini-HOWTO and see which one 
you'd rather manage.

> We have Red Hat Linux 9 installed on the computers. Will LVS work with them?

yes. (LVS should work with any distribution of Linux).

> PS : I am a student in my 3rd year and have taken up an elective (in
> college) of implementing "New Load Balancing Algorithms". Could anyone
> please mention a framework/API on which I could implement these new "load
> balancing" algorithms written by my Sir?

In LVS the load balancing algorithm is in the scheduler. 
There's a section in the HOWO on writing your own scheduler. 
Also look at feedbackd for dynamically controlling the 
loadbalancing. For LVS a new scheduler comes about when 
someone sees that something isn't working. I thought that lc 
and rr were all we'd need until Thomas Proell realised that 
with squids you always wanted a client going to the squid 
that had the content you wanted. There's not much point in 
implementing a new algorithm, unless you have a need for it.

Joe
-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
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