Forgive me if this has been discussed elsewhere (I know some of it has) but I was hoping for a bit of a steer on this one.
I work on a part time basis teaching Aeromedical retrieval for a University in Australasia and we are currently adding moodle to our portfolio of distance learning applications. Im actually based in the UK and am informally leading this project (due to some previous experience with LAMP).
I have a working moodle install on Cent on a UK VPS which I incredibly pleased with - so much so that I’m hoping to go live this semester and not next. One of my few issues surrounds Internet latency. Whilst most Universities need to service a relatively local population of students and faculty, our course members are literally spread out all across the world. Our tests have shown that connections from Europe are pretty quick, and make the system eminently usable, but from Aus and NZ to UK the latency makes the system a whole lot less attractive.
To get round this we would like to run mirror servers in the US, Middle East and Aus. So, to the crux of my question, and forgive me if it’s naive - WAN networking and replication is really not my thing. What is the best way of achieving this? My first idea was to run rsync on both the machines - each instance of rsync updating the files of the other servers overnight. Have not tried this yet but already I see storm clouds gathering if I do this with more than two servers.
Secondly, I read that keeping two or more mySQL servers in sync across a WAN can be a nightmare. Is this right or are there ways of replicating mySQL data across multiple servers a cross the WAN that live on geographically distanced VPS machines?
Although not great from a latency perspective, is it better to have a single mySQL server for all the instances but have the files on each machine? This means that the big bits of data that the students need to shunt around (assignments, essential readings etc) will be local to them and the other 'light' data will come from the mySQL server in London.
In short, it’s not the loading on the servers that will be the problem - I could comfortably manage all the students concurrently on the London server, nor is it the bandwidth out of London - it’s a good size pipe, it’s the Internet latency across the world that worries me.
Sorry for such a long post - any guidance or comment would be much appreciated.
What strikes me, is that this very Moodle site (moodle.org) with its huge number of users seems to work absolutely fine worldwidee - and it's (as far as I know) based in Perth, Australia.
While Moodle HQ is in Perth, the servers are hosted at theplanet.com Data Centre in Dallas .. ( ie big pipes )
Tracing route to moodle.org [188.8.131.52]
over a maximum of 30 hops:
1 <1 ms <1 ms <1 ms 192.168.2.254
2 <1 ms <1 ms <1 ms 192.168.9.1
3 * * * Request timed out.
4 239 ms 124 ms 158 ms 184.108.40.206
5 6 ms 27 ms 7 ms 220.127.116.11
6 45 ms 8 ms 6 ms 18.104.22.168
7 133 ms 159 ms 68 ms 22.214.171.124
8 127 ms * 68 ms 126.96.36.199
9 173 ms 149 ms 253 ms gi-0-0.akl-int-3.linktelecom.co.nz [188.8.131.52]
10 * 411 ms * ip-184.108.40.206.VOCUS.net.au [220.127.116.11]
11 539 ms 244 ms 214 ms ge-0-0-1-52.bdr01.sjc01.ca.vocus.net.au [18.104.22.168]
12 183 ms 240 ms 241 ms ge-4-21.car1.SanJose1.Level3.net [22.214.171.124]
13 281 ms 294 ms 348 ms vlan99.csw4.SanJose1.Level3.net [126.96.36.199]
14 373 ms 144 ms 139 ms ae-93-93.ebr3.SanJose1.Level3.net [188.8.131.52]
15 165 ms 202 ms 156 ms ae-2.ebr3.LosAngeles1.Level3.net [184.108.40.206]
16 163 ms 147 ms 159 ms ae-82-88.ebr2.LosAngeles1.Level3.net [220.127.116.11]
17 195 ms 189 ms 182 ms ae-3.ebr3.Dallas1.Level3.net [18.104.22.168]
18 180 ms 236 ms 192 ms ae-34-80.car4.Dallas1.Level3.net [22.214.171.124]
19 248 ms 238 ms 221 ms THE-PLANET.car4.Dallas1.Level3.net [126.96.36.199]
20 292 ms 234 ms 391 ms te9-2.dsr01.dllstx3.theplanet.com [188.8.131.52]
21 * * * Request timed out.
22 228 ms 211 ms 194 ms te5-1.car13.dllstx6.theplanet.com [184.108.40.206]
23 196 ms 195 ms 196 ms server10.moodle.com [220.127.116.11]
Thanks for your reply, sorry I have not responded earlier.
I have come to the conclusion that you are absolutely right and that with the right server resources Moodle should be scalable well from its server on a VPS farm in the UK.
Thanks again for your help, I'll let you know if we have any issues!
All the best,