Puppet users - Sep 2013 - Noob question about the ${name} variable

Greetings.

When defining a "file" resource, why does the ${name} variable
sometimes expand to the filename being maintained, and sometimes to the module
name?

Examples (in a module which, for simplicity, we will call "apache")
...

  file { ''/etc/httpd/conf/httpd.conf'' :
    ensure => file ,
    source => "puppet:///modules/${module_name}${name}" ,
  }

Here $name expands to "/etc/httpd/conf/httpd.conf", so
"source" expands to
"puppet:///modules/apache/etc/httpd/conf/httpd.conf".

  file { ''/etc/httpd/conf.d/ssl.conf'' :
    ensure  => file ,
    content => template ( "${module_name}{$name}.erb" ) ,
  }

Here $name expands to "apache", so the filename passed to template()
is "apacheapache.erb", rather than the expected and desired value
"apache/etc/httpd/conf.d/ssl.conf.erb".

Why does $name expand differently in these cases, and where did I miss this in
the documentation?

--
John Simpson <jms1@voalte.com>
Unix System/VM Developer and Engineering Operations, Voalte
+1 (941) 312-2830 x148

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On Sep 25, 2013, at 8:12 AM, John Simpson <jms1@voalte.com> wrote:
>  file { ''/etc/httpd/conf.d/ssl.conf'' :
>    ensure  => file ,
>    content => template ( "${module_name}{$name}.erb" ) ,
>  }
> 
> Here $name expands to "apache", so the filename passed to
template() is "apacheapache.erb", rather than the expected and desired
value "apache/etc/httpd/conf.d/ssl.conf.erb".
Is this the literal syntax?  Because you have "{$name}" instead of
"${name}".  I can''t explain why the former would expand the
way it does, unless the braces around the variable name have special meaning.  I
would expect you''d get the literal braces in the expanded value.  Not a
real answer, but it does look unintentional.

--
Brian Lalor
blalor@bravo5.org
http://github.com/blalor

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>   file { ''/etc/httpd/conf.d/ssl.conf'' : 
>     ensure  => file , 
>     content => template ( "${module_name}{$name}.erb" ) , 
>   } 
>
> Here $name expands to "apache", so the filename passed to
template() is
> "apacheapache.erb", rather than the expected and desired value 
> "apache/etc/httpd/conf.d/ssl.conf.erb". 
>
> Here you have syntax problem try,
content => template ( "${module_name}/${name}.erb" ) , 

Thanks and Regards,
Rahul Khengare,
NTT DATA OSS Center, Pune, India.

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On 2013-09-25, at 0819, Brian Lalor <blalor@bravo5.org> wrote:
On Sep 25, 2013, at 8:12 AM, John Simpson <jms1@voalte.com>
wrote:
> 
>> file { ''/etc/httpd/conf.d/ssl.conf'' :
>>   ensure  => file ,
>>   content => template ( "${module_name}{$name}.erb" ) ,
>> }
>> 
>> Here $name expands to "apache", so the filename passed to
template() is "apacheapache.erb", rather than the expected and desired
value "apache/etc/httpd/conf.d/ssl.conf.erb".
> 
> Is this the literal syntax?  Because you have "{$name}" instead
of "${name}".  I can''t explain why the former would expand
the way it does, unless the braces around the variable name have special
meaning.  I would expect you''d get the literal braces in the expanded
value.  Not a real answer, but it does look unintentional.
Sorry, I tried to remove a bunch of extraneous detail from my first message and
fat-fingered the variable.

The actual syntax, copied and pasted from the module, is:

  file { ''/etc/httpd/conf.d/ssl.conf'' :
    ensure  => file ,
    mode    => 0644 ,
    owner   => 0 ,
    group   => 0 ,
    content => template ( "${module_name}${name}.erb" ) ,
    notify  => Service[''httpd''] ,
    require => Package[''httpd''] ,
  }

When I try to apply this on my test machine, I get...

# puppet agent -t
Info: Retrieving plugin
Info: Loading facts in /var/lib/puppet/lib/facter/os_maj_version.rb
Error: Could not retrieve catalog from remote server: Error 400 on SERVER: Could
not find template ''apacheapache.erb'' at
/home/jms1/puppet/apache/manifests/init.pp:21 on node xxx
Warning: Not using cache on failed catalog
Error: Could not retrieve catalog; skipping run

--
John Simpson <jms1@voalte.com>
Unix System/VM Developer and Engineering Operations, Voalte
+1 (941) 312-2830 x148

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Hi John,
   Read my previous reply, 
>
>   file { ''/etc/httpd/conf.d/ssl.conf'' : 
>     ensure  => file , 
>     mode    => 0644 , 
>     owner   => 0 , 
>     group   => 0 , 
>     content => template ( "${module_name}${name}.erb" ) , 
>     notify  => Service[''httpd''] , 
>     require => Package[''httpd''] , 
>   } 
>
> The *''/''* is missing in between ${module_name} and
${name}
Thanks and Regards,
Rahul Khengare   

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On Wednesday, September 25, 2013 7:12:29 AM UTC-5, John Simpson
wrote:
>
> Greetings. 
>
> When defining a "file" resource, why does the ${name} variable
sometimes
> expand to the filename being maintained, and sometimes to the module name?


It doesn''t.  The ${name} variable always resolves to the name of the
class
or definition instance in which it appears, including when (as is often the 
case) it is used therein inside a resource declaration, such as of a File.  
Examples:

# Class definition:
class demo_class {
  # resource declaration:
  notify { ''demonstration resource1'':
    message => "The name of my class is ${name}"
  }
}
 
# Type definition
define demo_resource() {
  # resource declaration:
  notify { ''demonstration resource2'':
    message => "The name of my instance is ${name}"
  }
}

# Class declaration
class { ''demo_class'': }
# Will emit a notify message "The name of my class is demo_class"

# Class declaration
include  ''demo_class''
# Equivalent to the previous, so it will emit a notify message
# "The name of my class is demo_class" (but only one such if both
# declarations appear).

# Resource declaration
demo_resource { ''instance1'': }
# Will emit a notify message "The name of my instance is instance1"


Do not be confused by the curly braces of a resource declaration: they do 
not establish a new scope, so variable references appearing inside them 
mean the same thing that they do immediately outside.


John

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On 2013-09-26, at 0303, Rahul Khengare <rahulk1306@gmail.com> wrote:
> Hi John,
>    Read my previous reply, 
> 
>   file { ''/etc/httpd/conf.d/ssl.conf'' : 
>     ensure  => file , 
>     mode    => 0644 , 
>     owner   => 0 , 
>     group   => 0 , 
>     content => template ( "${module_name}${name}.erb" ) , 
>     notify  => Service[''httpd''] , 
>     require => Package[''httpd''] , 
>   } 
> 
> The ''/'' is missing in between ${module_name} and ${name} 
Sorry, but I wrote the line this way specifically because the first character of
the value of $name is "/". Adding an extra "/" between
"${module_name}" and "${name}" would result in
"apache//xxx.erb". Presumably the "//" wouldn''t
hurt anything (the Linux kernel ignores the empty directory element between the
two slashes when resolving the filename), but it wouldn''t have helped
either.


I did, however, figure out what the problem was. In this case, it was confusion
caused by either less-than-perfect documentation, or my own less-than-perfect
understanding of that documentation.

The confusion has to do with what the $name variable actually is. Essentially,
it does not refer to the item you''re declaring (in this case, a file.)
It refers to the object WITHIN WHICH you are declaring it.

So for a file declared within a class...

    class apache {
      file { ''blah'' :
        ensure  => file ,
        content => template ( "${module_name}${name}.erb" ) ,
      }
    }

the value of $name is "apache" (the name of the class.)

And for a file declared within a define...

    class apache {
      define configfile {
        file { $name :
          ensure  => file ,
          content => template ( "${module_name}${name}.erb" ) ,
        }
      }

      configfile { ''/etc/httpd/conf.d/01_aaa.conf'' : }
      configfile { ''/etc/httpd/conf.d/02_bbb.conf'' : }
    }

the value of $name, in both locations, is the value with which that
"define" is later instantiated.

So in the second example, $name would be either
"/etc/httpd/conf.d/01_aaa.conf" or
"/etc/httpd/conf.d/02_bbb.conf", depending on which
"configfile" object is being instantiated at the time.

The real problem I was trying to solve is that I didn''t want to have to
type each filename twice, primarily because it opens up a potential source of
errors if the names aren''t typed exactly the same. Creating a
"wrapper" around the file object allows the same name to be used
multiple times, without having to worry about the name potentially not being
identical. It also allowed me to include several other elements (such as
"owner", "mode", and "notify") which would
otherwise have had to be duplicated.

My thanks to everybody who offered advice.

--
John Simpson <jms1@voalte.com>
Unix System/VM Developer and Engineering Operations, Voalte
+1 (941) 312-2830 x148

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