Templating

The goal is to substitute variables into a template to produce a configuration file.

Variable scopes

The variables in our template come from multiple sources:

  • top-level global variables (from facter), e.g.
    • ::hostname
    • ::fqdn
  • class-level variables (inherited from Hiera), e.g.
    • port
    • database_name, database_user, database_pass
  • resource/low-level variables (defined in file resource), e.g.
    • service_name

File resource

This file resources composes the contents of the file from an EPP template, which in turn references the variables above.

  file { '/tmp/configuration.xml':
    ensure => 'present',
    content => epp('appserver/configuration.xml.epp', {
      'service_name' => "${::hostname}-appserver"
    }),
  }

Template

The template could use ERB (Ruby-like) or EPP, but for simplicity’s sake, we’ll stick with Puppet’s Embedded Puppet (EPP) syntax.

<?xml version="1.0" encoding="utf-8" ?>
<server address="<%= $::fqdn %>">
  <service name="<%= $service_name %>">
    <port number="<%= $appserver::port %>" />
  </service>
  <database name="<%= $appserver::database_name %>" username="<%= $appserver::database_user %>" password="<%= $appserver::database_pass %>" />
</server>

Open-source

All the code for these tutorials is available as part of DevOps-Workstream. The segments from this tutorial specifically make up puppet/tutorial/07-templating here on GitHub.

If you’d like to see all the previous and future installments of this tutorial, they’re available under the puppet tag.

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