[Server-devel] Nepal Server Open Issues

Tue Feb 12 12:07:46 EST 2008

Hi Sulochan et al,

Thanks for the details and closing off a bunch of issues. I think we are
converging on a short term design. Time permitting, I'll create a new
wiki page this week showing the April design. The existing page can
track the "Phase 2" design. Nice and simple for Phase 1 with XS doing
network access, basic web serving, caching and maybe filtering sounds
wise.

Here's what I see for phase 1:
- XS build 150 (unless Wad or someone else comes up with a must have
reason and stable build in time)
- No SSO (also means no Moodle tracking by student, grade or group)
- 2 x XS servers
- No automated XO backup on XS

Let me know if you agree and we can revisit all in phase 2 with a newer
XS build.

Still open questions on phase 1:
1 - Network design. 
I think we need this based on Wads comment it's the only one supported
for >150 Xos:
(ISP)-------------(hub)---------eth0 [XS] eth1 ------------  (WiFi)----[
XO ]

The only downside is when XS is down you're off the Internet and Library
server. A second Wifi AP between the hub and eth0 helps but requires
manual intervention (e.g. change WEP to open on XS failure). It also
leaves the Internet open (aka no filtering) on XS failure. The 2 x XS
design may help but needs more definition.

Will you have 2 x DSL lines, one for each XS? Should we consider the
second AP on each XS or start with the design above? Does your DSL line
ever go down and is that a major concern?

2 - 2 x XS design. 
We need to define the "backup" scripts which allow one to backup the
other. Also need to spell out the domain name and web site design.
Lastly, need to define how Xos "attach" to an XS and if we can/should
segment the mesh. Some high level options for 2 x XS boxes are:
- active/standby. Mirrored and may require manual intervention to bring
up standby on active failure.
- active/active mirrored and load balanced by DNS, client (XO) config or
other
- active/active one for Grade 6 one for Grade 2 with each serving the
other grade on failure. Needs client config or other method to load
balance with Xos sticky to the right XS for their grade.

I think Tony has been commenting on the last option but we need another
level of detail for that to make phase 1.

3 - On Squid. I think you want a full Moodle, library and activities
store on the XS.  That keeps your XS useful even if DSL line is down. In
this case, Squid is mostly for transparent proxy (TP = close to the
user, caches everything and saves WAN BW)). Also some reverse proxy (RP
= close to the server, caches server content only, offloads server CPU
and HD). I think you can add some commands to the squid.conf to do the
RP and persist the Library server content. That way, even if the kids
surf the Internet and cache a whole bunch of stuff the Library and
Moodle is always local on the XS. 

Maybe squid experts know the command to persist (aka flush last) a
domain name? Also, can a squid expert confirm how to ensure cached
content gets served even if the origin domain is unreachable?

If you have a second box in the school you could run Squid on one and XS
on the other. That keeps content local and does TP and RP. Only down
side is it needs more HW (more points of failure), network and
management. I would start with Squid on same box as XS for simplicity.

FYI on some good links:
I noticed a bunch of new activities on Nepal page.
http://www.olenepal.org/activities_download.html

Cross posting this from the developer list: 
For the archives and those interested, the scripts Uruguay used for
their deployment are in git at:
   http://dev.laptop.org/git?p=projects/ceibal-scripts;a=tree

I hope to actually get a complete build image at some point.  (Thanks
for cjb for pointing these out to me.)
 --scott http://cscott.net/ )
*******

Let me know if you want a translation. We probably need a point person
to write Nepal install scripts too. That will force us to define some XS
details (e.g. domain names, XO home pages, directory structures for
activity store, etc.).

On Wiki updates, thanks for the edits/additions and keep them coming.
I'll try to spend an hour cleaning and editing on Friday. I also owe
more edits/comments on redundancy design.

Thanks,

Greg S

PS sorry for the long post again! Let me know if the list see this as
SPAM and wants me to toggle it back.

_______________________________
From: sulochan acharya [mailto:sulochan at gmail.com] 
Sent: Tuesday, February 12, 2008 1:46 AM
To: Greg Smith (gregmsmi)
Cc: server-devel at lists.laptop.org
Subject: Re: [Server-devel] Nepal Server Open Issues

	Nepal team - here are a few questions, suggestions and decisions
needed:
	1 - Need to decide ASAP if we will deploy the new XS image or
the
	current one. Also, please confirm if we have two XS boxes in the
school
	or one.

>>Yeah i think we are going to use two XS boxes in each school, for
redundancy purpose as proposed by Tony and others.

	2 - I suggest that people try upgrading their XS to the latest
image and
	take notes on how its done. Even if we deploy OLPC_XS_150.iso it
helps
	to have docs on to re-image. We want to know what Nepal or user
specific
	content can be preserved. We may also want to upgrade modules
one at a
	time. Does anyone know of docs or best practices on upgrading
whole
	boxes or by components for LAMP servers?

>>The latest stable built is 150, and yeah we can update modules through
yum. 

	3 - Need closure on SSO. Pending Martin's comments on the
applicability
	of the existing paradigm, you should pick a solution. Sounds
like John W
	suggests no user tracking or possibly one of the work arounds.
	See item 3 at this link for proposed workarounds:
	If it's a workaround we better clarify which right away.

>>I dont see SSO working anytime soon. It would be great to have it,
because it would solve quite a few auth problems. If Ivan can make it
work great, but we should not depend on it at least fot the test phase. 

	4 - Based on SSO decision you need to confirm what kind of
Moodle
	interface and services will be in phase 1. My main question is
if we
	will use Moodle to access activities.

>>Needs testing. Will update later. 

	5 - On the school network. Can you confirm if we can get 2 x
router +
	wireless Access points per XS? We need to flush out the failure
cases
	and the available HW will have a big effect on that. Let us know
what HW
	is in place. If ts just a matter of buying a few Linksys
routers, I
	think we can find a way to do that.

>> The network structure might be a little different. Please take a look
at the attached file and let me know what you guys think. 

>>Moodle does not handle IP based authentication. 

>>I am attaching a file that shows cache and xs structure for the pilot.
I think its a good idea to run proxy and content on different machines.
On a long run it becomes more efficient to do it like that. It also
reduces content handling and traffic processing on the XS. What do you
guys think?