How to do it…

Here's an example of using inline_template:

Pass your Ruby code to inline_template within the Puppet manifest, as follows:

cron { 'chkrootkit':
  command => '/usr/sbin/chkrootkit >
    /var/log/chkrootkit.log 2>&1',
  hour    => inline_template('<%= @hostname.sum % 24 %>'),
  minute  => '00',
}

How it works…

Anything inside the string passed to inline_template is executed as if it were an ERB template. That is, anything inside <%= and %> delimiters will be executed as Ruby code, and the rest will be treated as a string.

In this example, we use inline_template to compute a different hour for this cron resource (a scheduled job) for each machine, so that the same job does not run at the same time on all machines. For more on this technique, see the Efficiently distributing cron jobs section in Chapter 5, Users and Virtual Resources.

There's more...

In ERB code, whether inside a template file or an inline_template string, you can access your Puppet variables directly by name using an @ prefix, if they are in the current scope:

<%= @name %>

If they are in another scope you can reference them using scope.lookupvar, as follows:

<%= "The variable from otherclass is " +
  scope.lookupvar('otherclass::variable') %>

You should use inline templates sparingly. If you really need to do some complicated logic in your manifest, consider using a custom function instead (see the Creating custom functions section in Chapter 8, External tools and the Puppet ecosystem).

See also