[Puppet Users] Refresh an exec only if another file changes

[Jesús M. Navarro]

Hi, list:

I'm trying to add a Debian-based Xen Dom0 server to puppet management.

One of the files I want to consider is /boot/grub/menu.lst since it contains
some Xen-related options.

When managing it by hand I'd produce a skeleton for menu.lst and then I'd
execute update-grub, which would look for avaliable kernels and would add
related configs to the menu.lst contents.

My first idea came in the lines of (within a class):
file {
"/boot/grub/menu.lst":
mode => "0644",
owner => root,
group => root,
notify => Exec["update-grub"],
source => "puppet:///s_virtualcluster/menu.lst";
}
exec { "update-grub":
path => "/usr/bin:/usr/sbin:/bin",
refreshonly => true,
}

But since update-grub changes /boot/grub/menu.lst itself, the menu.lst
template gets downloaded and update-grub triggered each time puppet runs.

Is there an ellegant manner to deal with it? (like downloading menu.lst to a
different path, and then run update-grub only if md5sum of the real menu.lst
has changed from previous puppet run or if the server version from menu.lst
has changed?

TIA.

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[Patrick]

I won't call this way elegant, but there is an easy way to do it.


file {
"/boot/grub/server_menu.lst":

mode => "0644",
owner => root,
group => root,

notify => Exec["updated_menu.lst"],
source => "puppet:///s_virtualcluster/menu.lst";
}

exec { "cp -p /boot/grub/server_menu.lst /boot/grub/menu.lst":

path => "/usr/bin:/usr/sbin:/bin",

alias => "updated_menu.lst",
refreshonly => true,

notify => Exec["update-grub"],
}

exec { "update-grub":
path => "/usr/bin:/usr/sbin:/bin",
refreshonly => true,
}

[Jesús M. Navarro]

Hi, Patrick:

On Wednesday 28 April 2010 23:42:38 Patrick wrote:
> On Apr 28, 2010, at 1:10 PM, Jesús M. Navarro wrote:
> > Hi, list:
> >
> > I'm trying to add a Debian-based Xen Dom0 server to puppet management.

[...]

> I won't call this way elegant, but there is an easy way to do it.
>
>
> file {
> "/boot/grub/server_menu.lst":
> mode => "0644",
> owner => root,
> group => root,
> notify => Exec["updated_menu.lst"],
> source => "puppet:///s_virtualcluster/menu.lst";
> }
>
> exec { "cp -p /boot/grub/server_menu.lst /boot/grub/menu.lst":
> path => "/usr/bin:/usr/sbin:/bin",
> alias => "updated_menu.lst",
> refreshonly => true,
> notify => Exec["update-grub"],
> }
>
> exec { "update-grub":
> path => "/usr/bin:/usr/sbin:/bin",
> refreshonly => true,
> }

First of all, thanks for your help. I think your idea covers the first part
of the equation but unless I misunderstood, it won't cope with the second
part.

From what I see, yours will cope with the case where I update menu.lst
server-side, but what if somebody changes the client's copy
of /boot/grub/menu.lst? It seems puppet won't notice it so won't recover
the "proper" contents (as per the puppetmaster idea of it). Am I right?

Cheers and thank you for your interest.

[Patrick]

You're right. It won't do that. Try removing refreshonly on the second command, and replacing it with an "unless" or "onlyif" that uses /usr/bin/diff.
-Patrick

[Peter Meier]

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> From what I see, yours will cope with the case where I update menu.lst
> server-side, but what if somebody changes the client's copy
> of /boot/grub/menu.lst? It seems puppet won't notice it so won't recover
> the "proper" contents (as per the puppetmaster idea of it). Am I right?

How do you detect whether update-grub or a human have edited the file?
As Patrick outlined this detection has then to go into onlyif or unless.

cheers pete
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[David Schmitt]

Puppet already provides for exactly this check. Add

checksum => md5

to the file and it will only notify when the actual contents change.


Best Regards, David
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