Puppet users - Sep 2013 - symlink creation using facter, but facter is nil at first run.

Hi all,

I''m trying to find a better way to implement this, but I can''t
think of. I
have a jdk module that requires to create a symlink to whatever version is
the one installed. Say I install jdk-6u35, it will create something like
/usr/java/jdk_1.6.35. I would like to create a symlink /usr/java/jdk whose
target would be /usr/java/jdk_1.6.35.

The point here isn''t to ask how to create the symlink - that''s
straightforward. I''m in a chicken-egg problem. I''m sure
there''s got a
better and easier way to do this that I can''t think of.

I wrote a facter to report the jdk version running. Based on the string
returned by the facter, it works great. However, I jdk is not installed,
this facter returns nil - the catalog is compiled and the value was nil at
compilation time - and the file resource, property target, fails. I bypass
this with an if clause and everything runs fine because jdk is already
there and the symlink will be created. I know I could tell my facter to
return something else (actually I create a link to latest, and that works,
but it''s a poor''s man solution).

Have any you run into this situation? Any suggestion? Not convinced if
facter is the way to go in this particular case.

Thanks,
-fred

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On Friday, September 20, 2013 10:30:46 PM UTC-5, Frederiko Costa
wrote:
>
> Hi all,
>
> I''m trying to find a better way to implement this, but I
can''t think of. I
> have a jdk module that requires to create a symlink to whatever version is 
> the one installed. Say I install jdk-6u35, it will create something like 
> /usr/java/jdk_1.6.35. I would like to create a symlink /usr/java/jdk whose 
> target would be /usr/java/jdk_1.6.35.
>
> The point here isn''t to ask how to create the symlink -
that''s
> straightforward. I''m in a chicken-egg problem. I''m sure
there''s got a
> better and easier way to do this that I can''t think of. 
>
> I wrote a facter to report the jdk version running. Based on the string 
> returned by the facter, it works great. However, I jdk is not installed, 
> this facter returns nil - the catalog is compiled and the value was nil at 
> compilation time - and the file resource, property target, fails. I bypass 
> this with an if clause and everything runs fine because jdk is already 
> there and the symlink will be created. I know I could tell my facter to 
> return something else (actually I create a link to latest, and that works, 
> but it''s a poor''s man solution).
>
> Have any you run into this situation? Any suggestion? Not convinced if 
> facter is the way to go in this particular case.
>
>
Facts are THE way to communicate information about the current state of 
your nodes to the master to inform catalog compilation.  If you have a 
chicken & egg problem then it is not facter''s fault, it is yours:
your
custom fact is not suitable for the use to which you are trying to put it.  
Evidently, it determines the JDK version by a mechanism that depends on the 
symlink you described, and clearly such a fact cannot be used to direct the 
form of the symlink.

You have at least two options:

   1. Come up with a better way to determine which JDK is installed.  For 
   example, if you are installing the JDK via your system''s packaging
system
   (yum / apt / etc.) then your custom fact could querythe package manager to 
   extract the information you want.
   2. Instead of inquiring which JDK version is installed, you could choose 
   what version you want to be installed, and have Puppet make it so.


John

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Hmm. Perhaps you could have something like this (assuming your fact is
called $jdk_version):

package { ''jdk'':
  ensure => latest,
}

if ($::jdk_version) {
  file { ''/usr/java/jdk'':
    ensure  => link,
    target  => "/usr/java/${::jdk_version}",
    require => Package[''jdk''],
  }
} else {
  exec { ''create-symlink'':
    command => ''/bin/ln -s /usr/java/jdk-* /usr/java/jdk'',
    path    => ''/bin'',
    creates => ''/usr/java/jdk'',
    require => Package[''jdk''],
  }
}

This way, in either case the jdk package would be installed first. If it
existed prior to the puppet run, the fact will evaluate to TRUE and the
file resource will ensure that the appropriate link exists. Alternatively,
if the package was not installed prior to the run, the fact will evaluate
to FALSE, but the exec will still create the appropriate symlink. But only
if the symlink doesn''t already exist.

You''ll still have a problem if the jdk package is updated by puppet,
however. In that case the fact would have the old version and try to ensure
that the link points to a non-existent target. Maybe there''s a way to
make
the exec work in that case, with a refreshonly or something, but I
can''t
quite think of it right now, because ln -s will fail if the link already
exists (even if it''s pointing to a target that no longer exists).

Chris


On Fri, Sep 20, 2013 at 9:30 PM, Frederiko Costa
<frederiko@gmail.com>wrote:
> Hi all,
>
> I''m trying to find a better way to implement this, but I
can''t think of. I
> have a jdk module that requires to create a symlink to whatever version is
> the one installed. Say I install jdk-6u35, it will create something like
> /usr/java/jdk_1.6.35. I would like to create a symlink /usr/java/jdk whose
> target would be /usr/java/jdk_1.6.35.
>
> The point here isn''t to ask how to create the symlink -
that''s
> straightforward. I''m in a chicken-egg problem. I''m sure
there''s got a
> better and easier way to do this that I can''t think of.
>
> I wrote a facter to report the jdk version running. Based on the string
> returned by the facter, it works great. However, I jdk is not installed,
> this facter returns nil - the catalog is compiled and the value was nil at
> compilation time - and the file resource, property target, fails. I bypass
> this with an if clause and everything runs fine because jdk is already
> there and the symlink will be created. I know I could tell my facter to
> return something else (actually I create a link to latest, and that works,
> but it''s a poor''s man solution).
>
> Have any you run into this situation? Any suggestion? Not convinced if
> facter is the way to go in this particular case.
>
> Thanks,
> -fred
>
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Hi Chris,

Thanks for your help.

Yes, that''s pretty much the approach I took. The only thing I changed
was
that my facter looks at the yum repo to strip out the version and returns
the version. So, there will have a value, even if jdk is not yet installed.
Previously, I was stripping out the version by looking at the output of rpm
-qf command, which would return nil in the first time I ran the agent. By
looking at the repo via ''yum info'', I can report the version
when my facter
compiles for the first time and package is not yet installed.

Does that make sense?

thanks


-frederiko



On Tue, Sep 24, 2013 at 9:44 PM, Chris McDermott
<csmcdermott@gmail.com>wrote:
> Hmm. Perhaps you could have something like this (assuming your fact is
> called $jdk_version):
>
> package { ''jdk'':
>   ensure => latest,
> }
>
> if ($::jdk_version) {
>   file { ''/usr/java/jdk'':
>     ensure  => link,
>     target  => "/usr/java/${::jdk_version}",
>     require => Package[''jdk''],
>   }
> } else {
>   exec { ''create-symlink'':
>     command => ''/bin/ln -s /usr/java/jdk-*
/usr/java/jdk'',
>     path    => ''/bin'',
>     creates => ''/usr/java/jdk'',
>     require => Package[''jdk''],
>   }
> }
>
> This way, in either case the jdk package would be installed first. If it
> existed prior to the puppet run, the fact will evaluate to TRUE and the
> file resource will ensure that the appropriate link exists. Alternatively,
> if the package was not installed prior to the run, the fact will evaluate
> to FALSE, but the exec will still create the appropriate symlink. But only
> if the symlink doesn''t already exist.
>
> You''ll still have a problem if the jdk package is updated by
puppet,
> however. In that case the fact would have the old version and try to ensure
> that the link points to a non-existent target. Maybe there''s a way
to make
> the exec work in that case, with a refreshonly or something, but I
can''t
> quite think of it right now, because ln -s will fail if the link already
> exists (even if it''s pointing to a target that no longer exists).
>
> Chris
>
>
> On Fri, Sep 20, 2013 at 9:30 PM, Frederiko Costa
<frederiko@gmail.com>wrote:
>
>> Hi all,
>>
>> I''m trying to find a better way to implement this, but I
can''t think of.
>> I have a jdk module that requires to create a symlink to whatever
version
>> is the one installed. Say I install jdk-6u35, it will create something
like
>> /usr/java/jdk_1.6.35. I would like to create a symlink /usr/java/jdk
whose
>> target would be /usr/java/jdk_1.6.35.
>>
>> The point here isn''t to ask how to create the symlink -
that''s
>> straightforward. I''m in a chicken-egg problem. I''m
sure there''s got a
>> better and easier way to do this that I can''t think of.
>>
>> I wrote a facter to report the jdk version running. Based on the string
>> returned by the facter, it works great. However, I jdk is not
installed,
>> this facter returns nil - the catalog is compiled and the value was nil
at
>> compilation time - and the file resource, property target, fails. I
bypass
>> this with an if clause and everything runs fine because jdk is already
>> there and the symlink will be created. I know I could tell my facter to
>> return something else (actually I create a link to latest, and that
works,
>> but it''s a poor''s man solution).
>>
>> Have any you run into this situation? Any suggestion? Not convinced if
>> facter is the way to go in this particular case.
>>
>> Thanks,
>> -fred
>>
>> --
>> You received this message because you are subscribed to the Google
Groups
>> "Puppet Users" group.
>> To unsubscribe from this group and stop receiving emails from it, send
an
>> email to puppet-users+unsubscribe@googlegroups.com.
>> To post to this group, send email to puppet-users@googlegroups.com.
>> Visit this group at http://groups.google.com/group/puppet-users.
>> For more options, visit https://groups.google.com/groups/opt_out.
>>
>
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