While you can deploy config files easily with Puppet as simple text files, templates are much more powerful. A template file can do calculations, execute Ruby code, or reference the values of variables from your Puppet manifests. Anywhere you might deploy a text file using Puppet, you can use a template instead.

In the simplest case, a template can just be a static text file. More usefully, you can insert variables into it using the ERB (embedded Ruby) syntax. For example:

  <%= @name %>, this is a very large drink.

If the template is used in a context where the variable $name contains Zaphod Beeblebrox, the template will evaluate to:

  Zaphod Beeblebrox, this is a very large drink.

This simple technique is very useful to generate lots of files that only differ in the values of one or two variables, for example, virtual hosts, and for inserting values into a script such as database names and passwords.