Evaluating EPP templates

Evaluating EPP templates that are in a template file

Put template files in the templates directory of a module. EPP files use the .epp extension.

To use a EPP template file, evaluate it with the epp function. For example:

# epp(<FILE REFERENCE>, [<PARAMETER HASH>])
file { '/etc/ntp.conf':
  ensure  => file,
  content => epp('ntp/ntp.conf.epp', {'service_name' => 'xntpd', 'iburst_enable' => true}),
  # Loads /etc/puppetlabs/code/environments/production/modules/ntp/templates/ntp.conf.epp
}

The first argument to the function is the file reference: a string in the form '<MODULE>/<FILE>', which loads <FILE> from <MODULE>’s templates directory. For example, the file reference ntp/ntp.conf.epp loads the <MODULES DIRECTORY>/ntp/templates/ntp.conf.epp file.

Some EPP templates declare parameters, and you can provide values for them by passing a parameter hash to the epp function.

The keys of the hash must be valid local variable names (minus the $). Inside the template, Puppet creates variables with those names and assign their values from the hash. For example, with a parameter hash of {'service_name' => 'xntpd', 'iburst_enable' => true}, an EPP template would receive variables called $service_name and $iburst_enable.

When structuring your parameter hash, remember:

• If a template declares any mandatory parameters, you must set values for them with a parameter hash.
• If a template declares any optional parameters, you can choose to provide values or let them use their defaults.
• If a template declares no parameters, you can pass any number of parameters with any names; otherwise, you can only choose from the parameters requested by the template.

Evaluating EPP template strings

If you have a string value that contains template content, you can evaluate it with the inline_epp function.

In older versions of Puppet, inline templates were mostly used to get around limitations — tiny Ruby fragments were useful for transforming and manipulating data before Puppet had iteration functions like map or puppetlabs/stdlib functions like chomp and keys.

In modern versions of Puppet, inline templates are usable in some of the same situations template files are. Because the heredoc syntax makes it easy to write large and complicated strings in a manifest, you can use inline_epp to reduce the number of files needed for a simple module that manages a small config file.

For example:

$ntp_conf_template = @(END)
...template content goes here...
END

# inline_epp(<TEMPLATE STRING>, [<PARAMETER HASH>])
file { '/etc/ntp.conf':
  ensure  => file,
  content => inline_epp($ntp_conf_template, {'service_name' => 'xntpd', 'iburst_enable' => true}),
}

Some EPP templates declare parameters, and you can provide values for them by passing a parameter hash to the epp function.

The keys of the hash must be valid local variable names (minus the $). Inside the template, Puppet creates variables with those names and assign their values from the hash. For example, with a parameter hash of {'service_name' => 'xntpd', 'iburst_enable' => true}, an EPP template would receive variables called $service_name and $iburst_enable.

When structuring your parameter hash, remember:

• If a template declares any mandatory parameters, you must set values for them with a parameter hash.
• If a template declares any optional parameters, you can choose to provide values or let them use their defaults.
• If a template declares no parameters, you can pass any number of parameters with any names; otherwise, you can only choose from the parameters requested by the template.