This is where custom facts allow us to run arbitrary code on the client side. Custom functions are a server-side technology that assist you in the compilation of a catalog. Functions are executed on the Puppet server. Puppet already includes several functions that are built-in, and additional ones are contained in Puppet Forge modules, particularly the stdlib module (see https://forge.puppet.com/puppetlabs/stdlib).
There are, in fact, three possible ways to create custom functions, although you are unlikely to use the first two, so I will just leave you with some links to the Puppet documentation for those options:
- You could write the function in Puppet DSL (see https://puppet.com/docs/puppet/5.3/lang_write_functions_in_puppet.html), although you'll be unable to take advantage of the more powerful Ruby API.
- You could write the function in the legacy...
