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Re: [K12OSN] Thoughts for my upgrade...



Chris Hobbs wrote:

Chris,

Have a look at later postings in the recent thread "sourceforge thin client project" in this forum.

My 6 new servers have come in, and I'm going to be upgrading to them over the holidays. I'm trying to simplify management of the servers as a group, and would like your thoughts on these ideas.


I have been working on the idea of 'simplifying larger installations' by abstracting the Servers and/or Services. I am nowhere near a complete concept, let alone a working solution, which is a pity, considering you are requesting exactly what I am building. Also, unfortunately, I have to postpone any serious Linux work for the moment while I am busy with my peak-season of employment...non IT related. 8-/


The primary server (SVHSAPP01) in the group has 4 fast, large scsi drives, and I'll be setting them up with software RAID1. Total formatted capacity will be about 100GB. This will contain /home for all users, and /home will be exported via nfs to the servers via a dedicated VLAN on my switch. (It's also shared via samba for windows users.)


RAID1 is mirroring ? Do you really need 4 drives as a mirror ? The Array will only be the size of a single drive, not the sum of the drives..


User and group info will be synched up using rsync, which is how I currently manage them. I then only have to add users and groups to SVHSAPP01. It works great, and is simpler and more robust than using NIS, though admittedly not realtime. However, I'm synchronizing now every two minutes, and it seems to work fine.


Do you have a reason why not to use LDAP to achieve this ?



I'm wondering if there's any reason I shouldn't export /usr, /opt, and /tftpboot from SVHSAPP01 to the other servers as well. In theory, none of those filesystems should be having anything written to them under normal circumstances. It would certainly make upgrading simple, as I'd only have to touch one machine.


I would suggest that the Terminal Servers' performance will suffer by reading its' binaries over NFS. IMO, each Terminal Server will be better to have its' own local binaries and libs.

I do agree with your sentiments about a simplified upgrade procedure, but I am thinking that to modify binaries and libs for a running machine would be fatal to it almost instantly, even if you could get past the locked (in-use) files.

A solution would be to reboot the server as a 'special-case' LTSP Terminal, with its' root filesystem unmounted, mount / RW, make your changes/upgrade and reboot it back into service as a Terminal Server. I am quite sure this could all be scripted from the 'Master' Server, and would make a valuable addition to automating larger LTSP installations.


Terminals would connect to SVHSAPP.silvervalley.k12.ca.us, which would resolve to the different appservers via round-robin DNS. This provides some rudimentary load balancing, and eliminates one step in our current login process, using the chooser screen to pick a server. Obvious downside is that if one server goes down, every n'th terminal will be forced to reboot to try to get to a different server, at least until I can modify the DNS or fix the server.


Yes, I have been unable to find a proper load balancer for XDMCP. That is, one the actually selects and allocates the least-loaded Server.

I cannot picture how to 'fail over' a client session. Currently, the User will lose their session, and be forced to logon anew. It may even result in a support call since the User will experience a frozen console. This is only my perception, and perhaps the clients' X Server will re-paint the 'login' screen almost immediately, or perhaps after a few mouse-clicks.


I had been considering mosix, but the majority of our users will be using Mozilla and OpenOffice most of the time, and since those don't migrate, we wouldn't see much balancing.


Have you considered using seperate Servers for these Apps ? Mozilla and O-O run well on their own, seperate machine. So you have a Terminal Server, Mozilla Server, and an OpenOffice Server..


All the best for your upgrade. Do keep us informed.


regards,
Steve






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