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So after yesterdays forrays, I've been doing more looking today. Basically we have virtualisation - which gives you the appearance of whole virtual machines, complete with kernel running - and these come in various guises - the faster ones running on processors that have a few extra instructions to support them, but some can still be reasonably fast even on processors without these instructions. Xen has been about for a long time, but KVM seems to be gaining popularity and has kernel support as standard now.
I don't currently have any hardware to support the fastest of vitualistions... It requires Intel or AMD chips some a few funky extra instructions...
The other type I've been looking at is "containers"... And this was attractive to me because of a timing issue required by asterisk.. and it looked potentially easy to implement - OpenVZ just uses the filing system, so you can access files inside the container from outside it - without having to use the network get in...
Containers potentially run at the native speed of the host system - the best virtual systems above can almost run at full speed, but they still have a bit of overhead. Containers appear ro be more flexible about memory and disk usage too - although I've not really looked at this in-depth with the virtual environments - they seem to me to be allocated a fixed wodge of memory at start time and that's it for their lifetime - containers just share the whole of available system memory, although there are mechanisms to impose limits.
And containers ought to work on any old hardware - I'm experimenting on an old 1.8GHz Celeron workstation with 256MB of RAM...
If you need to run windows under Linux or a different kernel, then virtualization would appear to be the way to go, otherwise Containers would be where it's at...
This was my starting page: http://virt.kernelnewbies.org/TechComparisonOpenVZ failed completely to work for me. Even trying the stock Debian kernels, it just wouldn't boot. Compiled didn't make any difference either and I'm not convinced there's any active support on OpenVZ, and both Ubuntu and Debian seem to have dropped support for it.
The next on the list is Linux-VSserver and this did actually work for me, however like OpenVZ, it still requires a wodge of patches applying to a stock kernel, and seems to want to use loopback block devices for the filesystem of each container which makes it hard to get files in/out of it while the container is live (use the network)
The third is LXC... And it seems to be used by IBM, so I thought I'd give it a go - wished I'd tried first as it is actually fully supported in stock kernels (although still 'experimental'), as of 2.6.29.
http://www.ibm.com/developerworks/linux/library/l-lxc-containers/All that's needed is the userland programs to utilise it - not standard under Debian Lenny, but it's in testing... (they are standard under Ubuntu (and the Ubuntu kernel supports it out of the box)
So-far so good.... And when I get more time I'll have more to say, but it's actually looking very good at this point.
Gordon -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/linux_adm/list-faq.html