how to pass parameters to puppet modules?

Question

What is the best practice for configuration of puppet modules? I have puppet 2.7.11. I find this way quite messy, it looks like using global variables.

node default {
   $always_apt_update = true
   include apt
}

Should I create class which would inherit most of configuration from the original? The documentation seems to have too many versions and I'm not sure which one applies for me.

UPDATE:

when I try this:

  class { 'apt': 
    always_update => 'true',
  } 

I get an error:

Error 400 on SERVER: Invalid parameter always_update at /etc/puppet/manifests/nodes.pp:32

Solution 1

You should use Parametrized classes instead of global variables.

For example:

node default {
  class {'apt': 
    always_update =>true 
  }
}
class apt ($always_update = true ) {
  // code 
}

node 'example.com' { 
  class { bar: }
}

See puppet documentation for more information:

• http://projects.puppetlabs.com/projects/1/wiki/Development_Language_Evolution#Parameterized+classes
• http://docs.puppetlabs.com/guides/language_guide.html#parameterised-classes

Solution 2

These answers seems a bit outdated, with new versions of puppet i.e 3.7.x, class parameters can be passed using Hiera. Resource like class declaration is not considered best practice anymore.

Although the second answer does use Hiera, but it is using ‘hiera’ function explicitly, which is again a not so advisable practice.

The new solution would look something like this:

/etc/puppet/manifests/site.pp:

node default {
    include apt
}

/etc/puppet/modules/apt/manifests/init.pp:

class apt ($always_update = true ) {
  // code 
}

/etc/puppet/hieradata/<filename>.yaml

apt::always_update: true

Hiera data yaml files can have different values of the parameter as required.

Solution 3

The recommended practice these days is to use Hiera. It's built into 3.x, but in 2.7 you need to install it separately.

You can then grab data from Hiera in your manifest for the apt class:

$always_apt_update = hiera("always_apt_update")

With a Hiera config like this..

:hierarchy:
  - %{::clientcert}
  - common

..the node (pulled from the clientcert fact) will be used as higher precedence in the lookup than the common.yaml file.

So, with always_apt_update: false in node1.example.com.yaml and always_apt_update: true in common.yaml, node1 will end up with that variable set to false while other nodes will have it default to true.

Comments

[Tombart]

yeah, that's what I was trying, but for 2.7 the syntax is slightly different: class { 'apt': always_update => true }

[Tombart]

I've upgraded to puppet 3.1.0, if I you exactly your code I get this: Could not parse for environment production: Syntax error at '='; expected '}'. Without parameters it works, but does not solve anything.

[Tombart]

Thanks, it looks interesting. Puppet is obviously going through rapid development and sometimes it's not clear what's the currently supported way.

[Kristaps]

edited post to reflect puppet 3 syntax

[Tombart]

I had there also error in declaration of that class, now it finally works. thanks!

[Felipe Alvarez]

What would the hiera file name be in this example case?