[Server-devel] CCCS XS deployment

[Martin Langhoff]

On Mon, Oct 12, 2009 at 2:50 AM, Jerry Vonau <jvonau at shaw.ca> wrote:
>> When I set up the first XS server back in march (0.5.1) there was a
>> lot more info on the Wiki about setting up multiple XS servers in one
>> network.  Does anyone have any of this info available still or does it
>> no longer apply?

I removed the info because we don't really support multiple XS servers
in one network. That model is old, from the days when we thought we
would strongly recommend active antennas.

If you have a really large school, the model is:

 - Build a network with many APs, all connected to a "network
backbone" (one or more switches). The network backbone must connect to
eth1 on the XS.

 - Only one XS. If you have many users, just aim for a high-spec
machine for the XS role.

 - If the traffic is too much even for the high-spec machine you have
as XS , you can setup machines for specific roles -- this will need
minor changes in the config of the main XS. For example:
   - If postgresql load is significant (mainly in disk IO, memory),
the pgsql-xs process can be moved to a different machine -- just a
vanilla Fedora server running postgresql.
   - If the http proxy load is significant (disk IO, memory), the
squid process can be moved to a separate machine.
   - If the Moodle (apache/php, affecting memory and cpu) load is
significant, move it to a separate machine.

Now... the heaviest load on the XS will be Moodle (Apache / PHP /
PostgreSQL); and I have a lot of experience with large scale moodle
installs for up to 120K users, with "concurrent" use peaking at a
couple of thousand. There the answer was a small cluster of x86
mid-range servers.

The very largest schools we are targetting for OLPC deployments have
have around 3K users. At most you'll see 500~800 concurrent users(*)
and that will probably melt the network before it even gets to the
server.

And any mid-range server of the current generation (multi-core, maybe
8GB RAM using PAE, some reasonably fast SATA disks) will handle that
and laugh in your face while it cooks some pasta for your dining
pleasure.

* Not concurrently connected, but requesting a page within the same 5s window.

cheers,


m
-- 
 martin.langhoff at gmail.com
 martin at laptop.org -- School Server Architect
 - ask interesting questions
 - don't get distracted with shiny stuff  - working code first
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