Puppet users - Nov 2013 - File() or Exec() temporary override?

Hi Puppeteers,

When you have complex/rich classes, and large numbers of machines/VMs,
sometimes there is a machine that needs a temporary override on a
file.

Is there a way to say something like... ?

  node ''fqdn'' { # I work for RL :-)
      include rl_users
      include rl_base
      include rl_webserver # defines /etc/httpd/conf.d/foo.conf
      ignore File[''/etc/httpd/conf.d/foo.conf'']
  }

or something conceptually equivalent?

I know of a couple inelegant options: I can disable puppet on that VM
for the duration, or comment out the relevant class.

A more precise override/ignore is of course better, as other
components of the configuration are still applied correctly.



m
-- 
 martin.langhoff@gmail.com
 -  ask interesting questions
 - don''t get distracted with shiny stuff  - working code first
 ~ http://docs.moodle.org/en/User:Martin_Langhoff

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On Tuesday, November 5, 2013 9:11:38 AM UTC-6, Martin Langhoff
wrote:
>
> Hi Puppeteers, 
>
> When you have complex/rich classes, and large numbers of machines/VMs, 
> sometimes there is a machine that needs a temporary override on a 
> file. 
>
> Is there a way to say something like... ? 
>
>   node ''fqdn'' { # I work for RL :-) 
>       include rl_users 
>       include rl_base 
>       include rl_webserver # defines /etc/httpd/conf.d/foo.conf 
>       ignore File[''/etc/httpd/conf.d/foo.conf''] 
>   } 
>
> or something conceptually equivalent? 
>
> I know of a couple inelegant options: I can disable puppet on that VM 
> for the duration, or comment out the relevant class. 
>
> A more precise override/ignore is of course better, as other 
> components of the configuration are still applied correctly. 
>
>
You could consider just shutting down or deactivating the puppet agent on 
the affected machine for the duration of the override.  For example, run

puppet agent --disable

there and afterward run

puppet agent --enable

.  If that''s not viable, then something close to the idea you proposed 
should be possible:

node ''fqdn'' { # I work for RL :-) 
  include rl_users 
  include rl_base 
  include rl_webserver
  File<| title == ''/etc/httpd/conf.d/foo.conf'' |> {
    ensure => ''present'',
    content => undef
    # override other properties to undef (no quotes)
    # as needed.
  }
}


John

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On Wed, Nov 6, 2013 at 9:55 AM, jcbollinger <John.Bollinger@stjude.org>
wrote:
> .  If that''s not viable, then something close to the idea you
proposed
> should be possible:
By "should be possible, do you mean that you know or think that Puppet
supports it?
> node ''fqdn'' { # I work for RL :-)
>   include rl_users
>   include rl_base
>   include rl_webserver
>   File<| title == ''/etc/httpd/conf.d/foo.conf'' |> {
>     ensure => ''present'',
>     content => undef
>     # override other properties to undef (no quotes)
>     # as needed.
>   }
> }
Does this syntax work, and does it elegantly override any other File
stanzas that point to that file path? Does content=>undef override
''source'' or do I need to also say source->undef ?

If that actually works, what other types support this trick?

thanks,




m
-- 
 martin.langhoff@gmail.com
 -  ask interesting questions
 - don''t get distracted with shiny stuff  - working code first
 ~ http://docs.moodle.org/en/User:Martin_Langhoff

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On Wednesday, November 6, 2013 9:01:17 AM UTC-6, Martin Langhoff
wrote:
>
> On Wed, Nov 6, 2013 at 9:55 AM, jcbollinger
<John.Bo...@stjude.org<javascript:>>
> wrote: 
> > .  If that''s not viable, then something close to the idea you
proposed
> > should be possible: 
>
> By "should be possible, do you mean that you know or think that Puppet
> supports it? 
>
>
I mean I believe the code I presented will accomplish your objective.

 
> > node ''fqdn'' { # I work for RL :-) 
> >   include rl_users 
> >   include rl_base 
> >   include rl_webserver 
> >   File<| title == ''/etc/httpd/conf.d/foo.conf''
|> {
> >     ensure => ''present'', 
> >     content => undef 
> >     # override other properties to undef (no quotes) 
> >     # as needed. 
> >   } 
> > } 
>
> Does this syntax work, and does it elegantly override any other File 
> stanzas that point to that file path? Does content=>undef override 
> ''source'' or do I need to also say source->undef ? 
>
>
There can be only one declaration for any resource.  There can be multiple 
overrides, but the result is undefined (evaluation-order dependent, to be 
precise) if any two override the same property of the same underlying 
resource.

 
> If that actually works, what other types support this trick? 
>
>
It is an application of general-purpose features of Puppet DSL, mainly 
resource collectors 
(http://docs.puppetlabs.com/puppet/3/reference/lang_collectors.html) and 
overriding / "amending" properties of declared resources 
(http://docs.puppetlabs.com/puppet/2.7/reference/lang_resources.html#adding-or-modifying-attributes).
Use of the special ''undef'' value in such context is documented
in the
related section on amending resource properties via class inheritance 
(http://docs.puppetlabs.com/puppet/3/reference/lang_classes.html#inheritance).

In other words, that approach should work with all resource types, 
including defined types.  It does not work with classes, however, even 
though classes can be declared via a syntax that looks like a resource 
declaration.  For this and other reasons, it is best to take the view that 
classes are not resources.


John

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