In this chapter, we'll cover how to deal with problems that may emerge while setting up and using Hiera. We'll also have a look at external node classifiers (ENC), which are used to apply classes to nodes. When problems arise, the ability to use Hiera and ENCs from the command line will allow you to quickly find where the errors have been introduced and which classes are being applied to your nodes.

Hiera is a great tool that reduces the complexity of your code by separating the data from the code and placing the data in a system where values are based on facts. Hiera is usually configured to use YAML files to look up values. In the next section, we'll examine some of the problems that are seen when using YAML files.