Puppet users - Jul 2013 - scope for templates that is called from a class that includes the class that calls the template.

hi,

trying to understand the scope for templates -- after reading 
http://docs.puppetlabs.com/guides/templating.html, got a question about the 
following,


class test::foo {

     file {
       <snip>


       content => template ("footemplate.erb"), 
     }

}


class test::foo2 {
      $var = blah, 
      class {''test::foo'' : 
      } 
}

so the question is if footemplate.erb uses variable $var as @var, is there 
a need for me to pass it as a argument within class
{''test::foo'': var =>
$var ?   My interpretation of templating.html is that all the variables 
that are in scope of the called class would be passed/available in the 
template hence i would need to pass it as an argument. 

Can anyone shed some lights on this?

Thanks 

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Hi Daniel,


What I''ve done in the past is:

Foo.erb
<% foobar = scope.lookupvar(''::somefact'')
  othervar   = scope.lookupvar(''class::variable'')
lastvar = scope.lookupvar(''myclass::myvar'')
fqdn = scope.lookupvar(''::fqdn'')
-%>
#this file generated automatically by puppet for <%=fqdn%>
#manual changes will be reverted


<% if foobar -%>
Foo = <%=foobar%>
<%end-%>
... <stuff and things here > ...


Not sure if there''s a better way, but I''m inter the impression
(correct me if I''m wrong here?) that scope.lookupvar will do the right
thing as often as is possible.

HtH!

Wolf
MobileMail
> On Jul 1, 2013, at 19:07, Daniel Jung <mimianddaniel@gmail.com>
wrote:
> 
> hi,
> 
> trying to understand the scope for templates -- after reading
http://docs.puppetlabs.com/guides/templating.html, got a question about the
following,
> 
> 
> class test::foo {
> 
>      file {
>        <snip>
> 
> 
>        content => template ("footemplate.erb"), 
>      }
> 
> }
> 
> 
> class test::foo2 {
>       $var = blah, 
>       class {''test::foo'' : 
>       } 
> }
> 
> so the question is if footemplate.erb uses variable $var as @var, is there
a need for me to pass it as a argument within class
{''test::foo'': var => $var ?   My interpretation of
templating.html is that all the variables that are in scope of the called class
would be passed/available in the template hence i would need to pass it as an
argument.
> 
> Can anyone shed some lights on this?
> 
> Thanks 
> -- 
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Hi Wolf,

I guess you can use the lookupvar and specifically call the variable from 
the class where it belongs to. That would be one method of doing it and 
probably works with Puppet 3.* as well. 
I just want to get my head around the scope while calling templates from a 
manifest. 

Thanks for the reply though! 

On Monday, July 1, 2013 7:04:14 PM UTC-7, Wolf Noble
wrote:
>
> Hi Daniel,
>
>
> What I''ve done in the past is:
>
> Foo.erb
> <% foobar = scope.lookupvar(''::somefact'')
>   othervar   = scope.lookupvar(''class::variable'')
> lastvar = scope.lookupvar(''myclass::myvar'')
> fqdn = scope.lookupvar(''::fqdn'')
> -%>
> #this file generated automatically by puppet for <%=fqdn%>
> #manual changes will be reverted
>
>
> <% if foobar -%>
> Foo = <%=foobar%>
> <%end-%>
> ... <stuff and things here > ...
>
>
> Not sure if there''s a better way, but I''m inter the
impression (correct me
> if I''m wrong here?) that scope.lookupvar will do the right thing
as often
> as is possible.
>
> HtH!
>
> Wolf
> MobileMail
>
> On Jul 1, 2013, at 19:07, Daniel Jung <mimian...@gmail.com
<javascript:>>
> wrote:
>
> hi,
>
> trying to understand the scope for templates -- after reading 
> http://docs.puppetlabs.com/guides/templating.html, got a question about 
> the following,
>
>
> class test::foo {
>
>      file {
>        <snip>
>
>
>        content => template ("footemplate.erb"), 
>      }
>
> }
>
>
> class test::foo2 {
>       $var = blah, 
>       class {''test::foo'' : 
>       } 
> }
>
> so the question is if footemplate.erb uses variable $var as @var, is there 
> a need for me to pass it as a argument within class
{''test::foo'': var =>
> $var ?   My interpretation of templating.html is that all the variables 
> that are in scope of the called class would be passed/available in the 
> template hence i would need to pass it as an argument. 
>
> Can anyone shed some lights on this?
>
> Thanks 
>
> -- 
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>  
>  
>
>
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On Monday, July 1, 2013 9:17:11 PM UTC-5, Daniel Jung
wrote:
>
> Hi Wolf,
>
> I guess you can use the lookupvar and specifically call the variable from 
> the class where it belongs to. That would be one method of doing it and 
> probably works with Puppet 3.* as well. 
> I just want to get my head around the scope while calling templates from a 
> manifest. 
>
>
Yes, you can use scope.lookupvar() to retrieve the value of a variable of 
any class by passing the qualified name of the variable.  And that is what 
your templates *should* do if they need to query variables from outside the 
local scope where they are evaluated.  This works in Puppet 2 and Puppet 3.

Before dynamic scoping was removed (i.e. before Puppet 3), a template 
might, under some circumstances, be able to directly access variables 
belonging to other scopes, such as in your example code.  That was never a 
good idea, however, for exactly the same reasons that dynamic scoping in 
general was not a good idea.

The potential gotcha with looking up variables of other classes is that you 
must make sure that a declaration of the host class has already been parsed 
before the template is evaluated.  That''s not necessarily a big
problem,
but you can expect to be bitten in the behind if you forget to do it.


John


John

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according to http://docs.puppetlabs.com/guides/scope_and_puppet.html
about dynamic lookup from an included puppet file:
puppet 2.7 warns about it, and puppet 3.2 stops working, as expected.

however,
about dynamic lookup from a template called on an included puppet file:
both puppet 2.7 and puppet 3.2 it works, without even a warning. (see in 
red the below example)

Why is that?
And so, does this mean that dynamic lookup is bad from a puppet file, but 
not from a template file?


See below a specific example:

test.pp
class c1 {
  $var = ''hello''
  notify {"var from c1: $var": }
  include c2
}

class c2 {
  notify {"var from c2: $var": }
  
  file { ''/tmp/file.txt'':
    content => template(''file.txt.erb''),
  }
}

class { c1: }

file.txt.erb
var from file.txt.erb: <%= @var %>


----
running with puppet 2.7.19:
$ puppet apply --templatedir templates/ test.pp
*warning: Dynamic lookup of $var at /vagrant/t1/test.pp:8 is deprecated.*For
more information, see
http://docs.puppetlabs.com/guides/scope_and_puppet.html. To see the change 
in behavior, use the --debug flag.
notice: var from c1: hello
notice: /Stage[main]/C1/Notify[var from c1: hello]/message: defined 
''message'' as ''var from c1: hello''
notice: /Stage[main]/C2/File[/tmp/file.txt]/ensure: defined content as 
''{md5}ea0d73f3957b0893f63e03cb9d8c9d98''
*notice: var from c2: hello*
notice: /Stage[main]/C2/Notify[var from c2: hello]/message: defined 
''message'' as ''var from c2: hello''
notice: Finished catalog run in 0.05 seconds

$ cat /tmp/file.txt 
*var from file.txt.erb: hello*


running with puppet 3.3.2:
$ puppet apply --templatedir templates/ test.pp
Notice: Compiled catalog for mac4c.local in environment production in 0.16 
seconds
Notice: var from c1: hello
Notice: /Stage[main]/C1/Notify[var from c1: hello]/message: defined 
''message'' as ''var from c1: hello''
*Notice: var from c2: *
Notice: /Stage[main]/C2/Notify[var from c2: ]/message: defined
''message'' as
''var from c2: ''
Notice: /Stage[main]/C2/File[/tmp/file.txt]/ensure: defined content as 
''{md5}ea0d73f3957b0893f63e03cb9d8c9d98''

$ cat /tmp/file.txt 
*var from file.txt.erb: hello*

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and according to http://docs.puppetlabs.com/guides/templating.html
*All of the variables visible in the current scope are available as Ruby 
instance variables*
but out of the scope variables should be accessed by scope.lookupvar.

so, why does the previous example works? why does file.txt get the
''hello''
value?
*var from file.txt.erb: hello*



On Wednesday, November 27, 2013 2:40:41 PM UTC+1, David Portabella
wrote:
>
> according to http://docs.puppetlabs.com/guides/scope_and_puppet.html
> about dynamic lookup from an included puppet file:
> puppet 2.7 warns about it, and puppet 3.2 stops working, as expected.
>
> however,
> about dynamic lookup from a template called on an included puppet file:
> both puppet 2.7 and puppet 3.2 it works, without even a warning. (see in 
> red the below example)
>
> Why is that?
> And so, does this mean that dynamic lookup is bad from a puppet file, but 
> not from a template file?
>
>
> See below a specific example:
>
> test.pp
> class c1 {
>   $var = ''hello''
>   notify {"var from c1: $var": }
>   include c2
> }
>
> class c2 {
>   notify {"var from c2: $var": }
>   
>   file { ''/tmp/file.txt'':
>     content => template(''file.txt.erb''),
>   }
> }
>
> class { c1: }
>
> file.txt.erb
> var from file.txt.erb: <%= @var %>
>
>
> ----
> running with puppet 2.7.19:
> $ puppet apply --templatedir templates/ test.pp
> *warning: Dynamic lookup of $var at /vagrant/t1/test.pp:8 is
deprecated.*For more information, see
> http://docs.puppetlabs.com/guides/scope_and_puppet.html. To see the 
> change in behavior, use the --debug flag.
> notice: var from c1: hello
> notice: /Stage[main]/C1/Notify[var from c1: hello]/message: defined 
> ''message'' as ''var from c1: hello''
> notice: /Stage[main]/C2/File[/tmp/file.txt]/ensure: defined content as 
> ''{md5}ea0d73f3957b0893f63e03cb9d8c9d98''
> *notice: var from c2: hello*
> notice: /Stage[main]/C2/Notify[var from c2: hello]/message: defined 
> ''message'' as ''var from c2: hello''
> notice: Finished catalog run in 0.05 seconds
>
> $ cat /tmp/file.txt 
> *var from file.txt.erb: hello*
>
>
> running with puppet 3.3.2:
> $ puppet apply --templatedir templates/ test.pp
> Notice: Compiled catalog for mac4c.local in environment production in 0.16 
> seconds
> Notice: var from c1: hello
> Notice: /Stage[main]/C1/Notify[var from c1: hello]/message: defined 
> ''message'' as ''var from c1: hello''
> *Notice: var from c2: *
> Notice: /Stage[main]/C2/Notify[var from c2: ]/message: defined
''message''
> as ''var from c2: ''
> Notice: /Stage[main]/C2/File[/tmp/file.txt]/ensure: defined content as 
> ''{md5}ea0d73f3957b0893f63e03cb9d8c9d98''
>
> $ cat /tmp/file.txt 
> *var from file.txt.erb: hello*
>
>
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Hi,

that''s interesting indeed. You may have stumbled upon a bug. You could
try and search http://projects.puppetlabs.com/issues/ for similar
reports. If there is none, feel free to open a new bug and supply your
example code.

If time allows, I''ll look into it over the weekend.

Cheers,
Felix

On 11/27/2013 02:50 PM, David Portabella wrote:
> and according to http://docs.puppetlabs.com/guides/templating.html
> /All of the variables visible in the current scope are available as Ruby
> instance variables/
> but out of the scope variables should be accessed by scope.lookupvar.
> 
> so, why does the previous example works? why does file.txt get the
> ''hello'' value?
> *var from file.txt.erb: hello*
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you are right, someone filled a bug ticket one month ago:
http://projects.puppetlabs.com/issues/22800


On Thursday, November 28, 2013 9:32:00 AM UTC+1, Felix.Frank
wrote:
>
> Hi, 
>
> that''s interesting indeed. You may have stumbled upon a bug. You
could
> try and search http://projects.puppetlabs.com/issues/ for similar 
> reports. If there is none, feel free to open a new bug and supply your 
> example code. 
>
> If time allows, I''ll look into it over the weekend. 
>
> Cheers, 
> Felix 
>
> On 11/27/2013 02:50 PM, David Portabella wrote: 
> > and according to http://docs.puppetlabs.com/guides/templating.html 
> > /All of the variables visible in the current scope are available as
Ruby
> > instance variables/ 
> > but out of the scope variables should be accessed by scope.lookupvar. 
> > 
> > so, why does the previous example works? why does file.txt get the 
> > ''hello'' value? 
> > *var from file.txt.erb: hello* 
>
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Hi,

I''ve taken a look into the issue and it would appear that your root
problem is wrong template syntax. The below is not strictly valid:

On 11/27/2013 02:40 PM, David Portabella wrote:
> file.txt.erb
> var from file.txt.erb: <%= @var %>
What works as expected:
> var from file.txt.erb: <%= var %>
or
> var from file.txt.erb: <%= scope.lookupvar("var") %>
The fact that the member variable syntax @var works at all is confusing,
and may be considered a bug. Will update Redmine accordingly. I believe
that the support for such templates should be deprecated if possible.

Thanks,
Felix

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Hi,
> What works as expected:
>> var from file.txt.erb: <%= var %>
using var instead of @var produces this warning on puppet 3:
*Warning: Variable access via ''var'' is deprecated. Use
''@var'' instead. *

and it''s explained here:
http://docs.puppetlabs.com/guides/templating.html

*Historically, all of the variables visible in the current scope were also 
available as Ruby methods — that is, fqdn, memoryfree, operatingsystem, 
etc., without the prepended @ sign. This style of reference caused problems 
when variable names collided with Ruby method names; its use emits 
deprecation warnings as of Puppet 3 and will be removed in Puppet 4. Please 
update any existing code which uses it and start any new code out with the 
@fqdn instance-variable syntax.*
> var from file.txt.erb: <%= scope.lookupvar("var") %>
yes, we need to use this function if we need to access 
someothermodule::var, or a hiera variable.
however, using this function for all variables in the current scope would 
be ugly.

> The fact that the member variable syntax @var works at all is confusing,
> and may be considered a bug.
yes. that''s what we are saying.

dynamic lookup in templates should show a warning in puppet 2.7, and stop 
working on puppet 3.

Regards,
David


On Sunday, December 1, 2013 11:07:26 AM UTC+1, Felix.Frank
wrote:
>
> Hi, 
>
> I''ve taken a look into the issue and it would appear that your
root
> problem is wrong template syntax. The below is not strictly valid: 
>
> On 11/27/2013 02:40 PM, David Portabella wrote: 
> > file.txt.erb 
> > var from file.txt.erb: <%= @var %> 
>
> What works as expected: 
>
> > var from file.txt.erb: <%= var %> 
>
> or 
>
> > var from file.txt.erb: <%= scope.lookupvar("var") %> 
>
> The fact that the member variable syntax @var works at all is confusing, 
> and may be considered a bug. Will update Redmine accordingly. I believe 
> that the support for such templates should be deprecated if possible. 
>
> Thanks, 
> Felix 
>
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Absolutely! Sorry I had missed the deprecation warning earlier.

Full agreement on all points.

Debugging away... :-)

On 12/01/2013 11:21 AM, David Portabella wrote:
> Hi,
> 
>> What works as expected:
>>> var from file.txt.erb: <%= var %>
> 
> using var instead of @var produces this warning on puppet 3:
> /Warning: Variable access via ''var'' is deprecated. Use
''@var'' instead. /
> 
> and it''s explained here:
http://docs.puppetlabs.com/guides/templating.html
> /Historically, all of the variables visible in the current scope were
> also available as Ruby methods — that is, fqdn, memoryfree,
> operatingsystem, etc., without the prepended @ sign. This style of
> reference caused problems when variable names collided with Ruby method
> names; its use emits deprecation warnings as of Puppet 3 and will be
> removed in Puppet 4. Please update any existing code which uses it and
> start any new code out with the @fqdn instance-variable syntax.
> /
> 
>> var from file.txt.erb: <%= scope.lookupvar("var") %>
> yes, we need to use this function if we need to access
> someothermodule::var, or a hiera variable.
> however, using this function for all variables in the current scope
> would be ugly.
> 
> 
>> The fact that the member variable syntax @var works at all is
confusing,
>> and may be considered a bug.
> 
> yes. that''s what we are saying.
> 
> dynamic lookup in templates should show a warning in puppet 2.7, and
> stop working on puppet 3.
> 
> 
> Regards,
> David
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In case someone''s keeping score - a patch has been posted to github and
linked from the Redmine issue. I''ve had feedback from
Puppetlabs'' Andy
Parker and it looks like this cannot be fixed before Puppet 4.x.

In the meantime, please be wary of relying on scoping effects concerning
variables used in templates with 3.x, because those will suddenly stop
working. For technical reasons, there can be no deprecation warning for
this scenario.

On 12/01/2013 11:24 AM, Felix Frank wrote:
> Absolutely! Sorry I had missed the deprecation warning earlier.
> 
> Full agreement on all points.
> 
> Debugging away... :-)
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