Using the Hiera functions, the data stored in Hiera can be retrieved by the Puppet Master while compiling the catalog. In our manifests, we can have something like the following:

$dns_servers = hiera("dns_servers")

Note that the name of the Puppet variable need not be the same as that of the Hiera one, so the previous code can also be as follows:

$my_dns_servers = hiera("dns_servers")

This assigns to the variable $my_dns_servers the top value (the first one found while crossing the hierarchy of data sources) retrieved by Hiera for the key dns_servers.

We can also merge arrays and hashes here; so in order to retrieve an array of all the values in the hierarchy's data sources of a given key and not just the first one, we can use hiera_array() as follows:

$my_dns_servers = hiera_array("dns_servers")

If we expect a hash value for a given key, we can use the hiera() function to retrieve the top value found, or we can use hiera_hash() to merge all the found values in a single...