Network Booting Ubuntu from NFS

We normally operate a citrix thin client environment (350 clients) where we load a windows desktop.
The clients are (mostly) atom 270's or atom 330's with 1GB or 2GB RAM. Some clients are lower spec (1GHz via with 512MB or 256MB).

We have recently been having trouble with citrix running on very high load, causing login/slowness problems. In order to solve this I have setup a network booting ubuntu installation. The Ubuntu boots fine from the network, mount nfs as a remote filesystem then runs applications locally, thus taking load off Citrix servers. we are in the process of testing this on a few computer and so far it looks ok - boot is fast, application run well. The setup was: windows logins through likewise, pam_mount for mapped homedrives and shared area, applciations are that don't run natively on linux run via through Citrix.

The problem is that I have no idea how to plan for capacity - how many NFS servers will I need per number of clients? any takers? 10 clients per server? 30? 50? 100? 300?

Also, I have no swapdrive. What should I do about that? do I need one?

The linux apps are fairly basic, FF, OpenOffice, VLC etc.

tia

Like the sound of this! :)

What spec's the NFS box in play?
Is it doing anything else?
How big is your ubuntu image?
Is it on a gig feed?

I'd get 10 of them connecting to it and look at the box itself, check it's I/O on the fixed disks and the network, see if its busy or not and apply some pressure to give it some grief.

Having no swap to me is a no no, I know some people are quite happy with the amount of memory but I prefer knowing I have a buffer to give me time to upspec a box if necessary before the kernel starts chopping away at the processes.

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What spec's the NFS box in play?

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dual Xeon 2.2 2GB IIRC.

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Is it doing anything else?

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It provides the tftp boot image, it also is a tftp server for the thinstation that this system is designed to replace.

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How big is your ubuntu image?

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It's 3GB in total - but that doesn't all get loaded on boot, they 'sit' on the NFS disk, same as they would with any other disk. stuff only gets loaded to ram as and when (except the kernel, gnome etc)

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Is it on a gig feed?

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network to backbone is 1GB then 100Mb to the desktop (although some of the clients have 1gb nics, they are not in use)

We did try booting a class of 30 all at one, they all loaded reasonably quickly (except 2 that errored) We didn't try logging in or with any children. Just want to get an idea of how many NFS servers to put in before it all falls flat on its face. We're going to be trialling a geography class of 30 using lincity-ng (which doesn't run on citrix, but does on ubuntu).

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Having no swap to me is a no no,

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thats what I thought to. not sure what to do about that? nfs swap?

the other thing I didn't really think through - what happens when 100 clients all boot up using the same filesystem? /var/log ? any ideas ?

To awnser some of my own questions:

https://help.ubuntu.com/community/DisklessUbuntuHowto

(wish I saw this before I started)

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f you are going to have multiple systems share this root you need to make sure some directories like /var/run, /var/lock and /tmp are mounted in tmpfs so different systems won't be conflicting into each other.

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Adding a swap file
In case you do need or want to set up a swapfile, here's what I did to get one working:

sudo apt-get install dphys-swapfile
this package sets up a swap file at /var/swap that is 2x your current ram. however, it still doesn't setup the swapfile on its own, though it does try. to get the swap file working the rest of the way, do:

sudo losetup /dev/loop0 /var/swap
sudo swapon /dev/loop0
then, run top and you will see you have a swap file. however, put in as much ram as you need for what you are going to run, and just look at your swap file as "in case of emergency", because it is not efficient as a ram or a regular swap file, but should keep something from crashing. I'm running mythtv on top of a full feisty desktop, and tried it with 256mb ram, and myth-frontend would crash when i would try to bring it up. with the swap file, it would launch, but would take a while. i added an additional 256mb to bring the total to 512mb and it runs flawless, and i add the swap file just in case. i just make a script for it to set up the swap file at boot

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sorry fella, didn't see your update.

Will post soon.

no worries, It's turning out more complicated than I anticipated. I can get one machine to boot fine, the others are having auth errors and about 10% don't boot at all (complain / is already mounted) I think the hacks suggested int the file above will help with that.
The load on the NFS server is surprisingly reasonable when 30 clients boot - but I couldn't log in so still no idea about general usability.