[olpc-software] Servers

[Jim Gettys]

On Thu, 2006-03-30 at 11:30 +0700, James Clark wrote:
> On Wed, 2006-03-29 at 16:59 -0500, Christopher Blizzard wrote:
> 
> > The model that we've been talking about using is that there's a small 
> > server that sits in each school.  This server isn't really anything more 
> > than the laptop that you see with a disk enclosure added to the back to 
> > a USB port.  The idea is that the software and experience is as close to 
> > the same as the laptop itself.  That is, it's largely autonomous and 
> > self managing, patches are applied in exactly the same way, etc.  The 
> > only difference being some switches that are flipped that say "I'm a 
> > server" and then it starts acting like one.
> 
> I'm glad you've raised the issue of servers.  I definitely think we need
> a server in each school, and I agree it needs to self-managing.
> However, I'm a bit doubtful whether the laptop hardware has sufficient
> horsepower for this, in particular RAM.
> 

We've only considered that for the smallest schools without power, where
every watt counts.

> What were you thinking of running?  My list is something like this:
> 
> dnsmasq
> postfix
> dovecot
> apache httpd
> horde/imp (for webmail)
> ejabberd
> moodle (needs PHP and mysql)
> LAMS (probably a bit traditional for the OLPC guys :-)
> openldap (so there's one user database shared by everything)
> squid
> squidguard (web filtering)

A similar list, along with some other items: for example, there is a
very nice open source library application (check in/check out,
circulation control, etc).

Squid is problematic due to lack of IPv6 support, and the fact that
development in general seems to have stopped on it, when I was
investigating some weeks ago.  There are alternatives that seem more
viable at this date.

> 
> I would also want to have the sources for everything and a complete
> tool-chain so that schools could rebuild a laptop image.  Without this,
> people's ability to tinker is going to be very limited.
> 

Yup.

> The largest schools in Thailand have more than 4,000 children.
> Supporting all of the above for 4,000 users in 128Mb RAM doesn't seem
> practical to me.

Yup.  I'd expect to run something considerably bigger.

> 
> Wouldn't a conventional (in the hardware sense) server be more
> appropriate?  

Of course, in large schools.

> Of course, in the least developed countries, that might
> not be practical from a financial point of view or from a hardware
> durability point of view. However, in a relatively well-developed
> country like Thailand, I think things would work much better with a
> decent server.

Please do.

> 
> A related issue is networking.  In all but the smallest schools, I would
> envisage deploying some number of cheap, commodity access points and
> having them connected via wired ethernet.  

Most commodity access points don't work well with large numbers of
clients; their design center is a house with a few users. Identifying
pretty cheap, access points that don't have this problem would be good
to do.

The laptops, even used as an access point, will function much better
than the typical cheap access points you buy in a store.  So at least we
have an upper bound on the cost of access points.

> I would also want the server
> to be connected via wired ethernet. (I guess you could plug in a USB2
> ethernet adapter to OLPC.)  Serving 4,000 users wirelessly doesn't seem
> practical to me.

Schools that size will probably require some more serious network
engineering.

> 
> I'm guessing schools would also want a CD writer.  Once you add in the
> costs of external ethernet, external hard disk enclosure, external CD, I
> think using the OLPC laptop as a server starts not to make much sense
> financially either.  The cost of a low end PC would be only a small
> percentage (if any) more, especially if you set things up so the server
> can work headlessly without a monitor, and you would get a lot more
> horsepower.

As I said, the only time it may make sense to use the laptop that way is
in power starved environments, much less of a problem in Thailand than
other parts of the world. Having spent some time chatting with a
representative of Nigeria, many of their schools have no power at all.
Alternatives are generators, presenting logistical challenges with fuel,
or solar cells, in which case power will be quite limited.

Even so, Michail Bletsas has found another small, cheap, lowe power box
that is probably preferable for a small low power server than using the
laptop.

> 
> I think doing the server-side software for OLPC is a very substantial
> task and I don't see a lot of overlap with the laptop software.  With
> the server, I want an appliance-like user experience: just plug it in
> and it works; there's not much admin apart from user management.
> Whereas people should be free to break their own laptops, I don't think
> I would want people tinkering with the server.  Also I don't think a
> regular Linux distribution is going to work: that would require way too
> much system administration expertise.

The Skolelinux people in Norway have done a lot of work in this area,
and we will to (and will pick their brains.  Walter Bender is planning a
trip to go visit them.  And I plan to visit the Extremadura/Andalucia
deployments in Spain in June to understand what they've done in this
area.

                                    - Jim

-- 
Jim Gettys
One Laptop Per Child