Puppet users - May 2008 - Functions vs. Module Plugins vs. Facts

Hey all,

I am trying to get a modified hostname (converting "blah-1234567" to
"1234567") to use in my manifests and templates.  I have it working
for
templates by using Ruby (*<%=
hostname.split(''-'').pop.downcase %>*) but I
haven''t been able to use it in manifests because they don''t
process ERB.
 The way I see it I could do one of two things; create a custom function or
create a custom fact.  I think I would rather build a server-side function
but I haven''t had much luck getting them to work.  So I started looking
at
creating a custom fact but the Wiki/documentation is quite convoluted and I
haven''t been able to gain any ground there either.

Which method would be better, simpler, and less client-side intrusive?  Does
anyone have an example of a custom function that I could copy?  Where on the
server to place it?  I tried creating my own function in
/usr/local/lib/site_ruby/puppet/parser/functions/keyname.rb but it''s
giving
me a "...private method ''split'' called for
["blah-1234567"]:Array at ..."
error.  Or should I just use a facter fact?  I tried to make sense of the
Wiki but its just not sinking in.  It doesn''t help that Puppet is in
its
growth stage right now so some of the information out there is no longer
valid.  My copy of "Pulling String with Puppet" is on its way, however
I''m
afraid that by the time it gets here it will be out of date.  :(

Anyway, I''m running Puppet 0.24.4 on Debian Etch on both client &
server and
here is my first try at a puppet function:

# keyname.rb
module Puppet::Parser::Functions
  newfunction(:keyname, :type => :rvalue) do |args|
    args.split(''-'').pop.downcase
  end
end

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You might also consider using the generate function to call an external
script. We''re still developing our puppet framework, but something
we''ve
come to found handy is to use generate to invoke a shell/ruby/whatever
program and to set it in a variable. Advantages that we''ve found for
this are:

1. It keeps the template files from being cluttered with ruby snippets
which is a big plus as the template seems to be the last place that I
look when I''m asking ''how was this value computed?''

2. The generated value is reusable in different templates and puppet
subclasses

3. The value generation occurs outside of puppet and is usable to other
non-puppet programs and scripts. We have a script like this that
determines the puppetmaster url for a particular node and use it in both
a xen role script as well as a puppet manifest.

4. It is not a custom fact, and does not inherit any issues from plugin
syncing.

James.

Richard Hurt wrote:
| Hey all,
|
| I am trying to get a modified hostname (converting "blah-1234567" to
| "1234567") to use in my manifests and templates.  I have it working
for
| templates by using Ruby (/<%=
hostname.split(''-'').pop.downcase %>/) but
| I haven''t been able to use it in manifests because they
don''t process
| ERB.  The way I see it I could do one of two things; create a custom
| function or create a custom fact.  I think I would rather build a
| server-side function but I haven''t had much luck getting them to
work.
| So I started looking at creating a custom fact but the
| Wiki/documentation is quite convoluted and I haven''t been able to
gain
| any ground there either.
|
| Which method would be better, simpler, and less client-side intrusive?
| Does anyone have an example of a custom function that I could copy?
| Where on the server to place it?  I tried creating my own function in
| /usr/local/lib/site_ruby/puppet/parser/functions/keyname.rb but it''s
| giving me a "...private method ''split'' called for
["blah-1234567"]:Array
| at ..." error.  Or should I just use a facter fact?  I tried to make
| sense of the Wiki but its just not sinking in.  It doesn''t help that
| Puppet is in its growth stage right now so some of the information out
| there is no longer valid.  My copy of "Pulling String with Puppet"
is on
| its way, however I''m afraid that by the time it gets here it will be
out
| of date.  :(
|
| Anyway, I''m running Puppet 0.24.4 on Debian Etch on both client &
server
| and here is my first try at a puppet function:
|
| # keyname.rb
| module Puppet::Parser::Functions
|   newfunction(:keyname, :type => :rvalue) do |args|
|     args.split(''-'').pop.downcase
|   end
| end
|
| |
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On May 2, 2008, at 11:25 AM, Richard Hurt wrote:
>
> # keyname.rb
> module Puppet::Parser::Functions
>   newfunction(:keyname, :type => :rvalue) do |args|
>     args.split(''-'').pop.downcase
>   end
> end
>
args is an Array, and I assume you want the numeric portion of  
"blah-1351515", so you just need:

keyname = args[0].split(''-'')[1].downcase

Assuming you''ll only ever have a single argument. (Use a variable to  
avoid the wonderful memory leak split can introduce.)

-Blake

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Hi
> Which method would be better, simpler, and less client-side intrusive? 
Does
> anyone have an example of a custom function that I could copy?  Where on
the
> server to place it?  I tried creating my own function in
> /usr/local/lib/site_ruby/puppet/parser/functions/keyname.rb but
it''s giving
> me a "...private method ''split'' called for
["blah-1234567"]:Array at ..."
> error.  Or should I just use a facter fact?  I tried to make sense of the
> Wiki but its just not sinking in.  It doesn''t help that Puppet is
in its
> growth stage right now so some of the information out there is no longer
> valid.  My copy of "Pulling String with Puppet" is on its way,
however I''m
> afraid that by the time it gets here it will be out of date.  :(
i would simply add a custom fact. With that you can do all want you  
want and reuse this variable in any location (define, manifests,  
templates).

greets pete

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Richard Hurt wrote:
> there is no longer valid.  My copy of "Pulling String with
Puppet" is on
> its way, however I''m afraid that by the time it gets here it will
be out
> of date.  :(
As the book is POD - Print on Demand - I''ve been fixing all the errata
and some issues with the changes Luke has been submitting.  So it should
be still up to date.

Regards

James Turnbull

- --
James Turnbull (james@lovedthanlost.net)
- --
Author of:
- - Pulling Strings with Puppet
(http://www.amazon.com/gp/product/1590599780/)
- - Pro Nagios 2.0
(http://www.amazon.com/gp/product/1590596099/)
- - Hardening Linux
(http://www.amazon.com/gp/product/1590594444/)

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