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Re: [Xen-users] cron and domU's

To: Javier Guerra <javier@xxxxxxxxxxx>
Subject: Re: [Xen-users] cron and domU's
From: Israel Garcia <igalvarez@xxxxxxxxx>
Date: Mon, 14 Dec 2009 15:11:57 -0500
Cc: Xen Users <Xen-users@xxxxxxxxxxxxxxxxxxx>
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On 12/14/09, Javier Guerra <javier@xxxxxxxxxxx> wrote:
> On Mon, Dec 14, 2009 at 11:30 AM, Israel Garcia <igalvarez@xxxxxxxxx> wrote:
>> Hi, I'm getting bad performance on domUs cause all dom0 and domUs
>> crontab's are setup at same hour 6,25AM. I want to ask you if there's
>> something I can use to centralize setup of all crones from domU
>> instead of setting up every domU's cron (to run in different hours)
>> manually?
> I see at least two levels of answering:
> A) yes, there might be some kind of centralized contrab config tool.
> This isn't exclusive to Xen, any datacenter with several similar
> machines must setup backups and other heavy processes to avoid
> fighting for some scarce resource (like a fileserver, or a shared
> device).  At the very least, there's a webmin module for 'cluster cron
> jobs' but this might be exactly the opposite (it seems to try to
> execute all at the same time)\
Hi Javier,

A) is what I'm looking for...:-) but I don't like webmin for this job..

> B) do you mean running cron in Dom0 instead of on all DomU's?
>   B.1) on one side it could be reasonable, after all that's
> (conceptually) how backup servers do: they have their own scheduler
> and 'pull' the data from the running servers.  still, i wouldn't run
> it in Dom0, but on the machine (virtual or real) that manages the
> resource.  IOW, not a 'cron server', but a schedule for backups on the
> backup server, a schedule for updating mirrors on some mirror server,
> a schedule for OS updates on some local updates mirror, etc.
>   B.2) if you mean having all that's cron-able managed from Dom0; then
> no, that's not how you should do it.  First of all, that would mean
> that this single machine can execute any administration command
> directly on every machine, creating a HUGE security issue.  And second
> because then you go in a slippery slope of putting everything that's
> centralizable on Dom0 (first the cron, then logfiles, oh and logrotate
> too, the OS updates, why not the users logins, later the SELinux
> profiles, etc).  soon the DomUs are limited to a single process each,
> and a big, fat Dom0.  Much better would be just forget about
> virtualization, and simply run several processes on a single OS
> instance.  after all, that's what shared hosting services do

I'll not manage all crontab on a dom0 neither domUs', maybe from other server..

thanks for your anwer


> --
> Javier

Israel Garcia

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