[lug] virtualization first boot question

karl horlen horlenkarl at yahoo.com
Tue Sep 14 17:49:16 MDT 2010

although my question is xen specific since that's what i'm currently exploring, i may turn out using an alternative like kvm, virtualbox, etc.  so this question is really posed generically.

lets say i'm running an apache web server at known public ip addresses.  it's been running well for a long time but now i want to make that same server a virtual server.

i need to download xen kernel and accompanying xen related tools (if another virtualization method is used, substitute appropriate pkgs).

my questions

1) when i reboot my server with the xen kernel, and assuming i don't create any additional virtual servers, am i correct in assuming that all services (in my case apache, but any other services listening on an ip address at a given port would qualify as well) will work exactly as they did in the non virtual kernel?  meaning i don't have to screw with ip addresses, networking config etc post xen boot?  

i believe the real physical networking interface and it's associated config *pre* virtualization simply gets bridged and then the config (public ips, etc) gets automatically copied to the virtual interfaces that now live in the first virtual machine / master domain (see #2) right?

2) the way i understand it is that when xen (i presume it's similar in other virtualization solutions but maybe i shouldn't) boots, it immediately creates dom0.  dom0 essentially and transparently (unless you tell it otherwise via configuration) simply virtualizes your existing networking interfaces within dom0.  dom0 becomes the "default operating container" for what was "your old non virtual" system.  everything runs under dom0 until and unless you specifically start creating domUs to house other virtual servers and systems.  

the terminology is confusing but what i'm getting at is whether somebody can confirm for me that dom0 essentially equals the old server "getting shoved" into a (the first master) virtual container - .  meaning i don't need to perform any monkeying around with networking to get my services to work in the virtualized reboot?  

what i'm asking is if dom0 is a synonym for the old, base, non-virtualized system?

again, i just want to know that my base system will continue to function normally on the reboot.  and then a reconfirm that the base system essentially is dom0 from a theoretical, technological understanding standpoint.

my plan is to not screw with the original base system.  the goal of adding virtualization to an existing server is to leave what i have in tact and then simply add new functionality to the new virtual machines via domUs.

whew.  hope that makes sense.  i've been through the documentation but the dom0 thing is sort of only nebulously explained.



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