Puppet : how to append a string as new item into existing array ?

What is hiera?

Hiera is simple Lightweight Pluggable Hierarchical Database. It is a key/value lookup tool for hiera_lookupiguration data. Key/value may be string, array or hash.

Using Hiera

Suppose you have a a_hiera_hash in your yaml. It has a_hiera_key in two different yaml. At one place it is string ( hiera/location/dc1.yaml ) and at another place it is array (hiera/location/dc2.yaml)

==> hiera/location/dc1.yaml

a_hiera_hash:
    a_hiera_key: item_string


==> hiera/location/dc2.yaml

a_hiera_hash:
    a_hiera_key:
        - item_one
        - item_two
        - item_three

Adding a string in a string or array returned by hiera_hash

Now, if you want to add another string 'item_string_2' at the end of a_hiera_hash, there are 2 cases:

Case-1:

system1.dc1.com - a system in DC1 - For this system, a_hiera_key will be evaluated as string.

hiera_lookup = hiera_hash('a_hiera_hash', {})
hiera_lookup['a_hiera_key'] = 'item_string'  << this is what we will get

So we need to add 'item_string_2' at the end of above string. Puppet code will look like below.

        $a_hiera_key = $hiera_lookup['a_hiera_key']
        $a_hiera_key_new = "${a_hiera_key} item_string_2"
        $a_hiera_key = $a_hiera_key_new

Case-1:

system2.dc2.com - a system in DC2 - For this system, a_hiera_key will be evaluated as array.

hiera_lookup = hiera_hash('a_hiera_hash', {})
a_hiera_hash['a_hiera_key'] = [ 'item_one', 'item_two', 'item_three' ] << this is what we will get

So, now we need to add 'item_string_2' string as a new item of above array ! (type mismatch)


There is no straight way to add string as a new item of array item ! 

1- Convert array item into space seprated string using join library function - 'item_one item_two item_three'

        $a_hiera_key = join($hiera_lookup['a_hiera_key'], ' ')


2- Add 'item_string_2' at the end of string - 'item_one item_two item_three item_string_2'

        $a_hiera_key_new = "${a_hiera_key} item_string_2"

3- Split string using space a separator to make an array using split function- [ 'item_one', 'item_two', 'item_three', 'item_string_2' ]

         $a_hiera_key = split($a_hiera_key_new, ' ')



So, puppet code will look like something this.

hiera_lookup = hiera_hash('a_hiera_hash', {})

      if is_array($hiera_lookup['a_hiera_key']) {
        $a_hiera_key = join($hiera_lookup['a_hiera_key'], ' ')
        $a_hiera_key_new = "${a_hiera_key} item_string_2"
        $a_hiera_key = split($a_hiera_key_new, ' ')
      } else {
        $a_hiera_key = $hiera_lookup['a_hiera_key']
        $a_hiera_key_new = "${a_hiera_key} item_string_2"
        $a_hiera_key = $a_hiera_key_new
      }


NOTE:
If dc1.yaml also has array (similar to dc2.yaml), hiera_has will automatically merge 2 arrays. For eacmple, if dc1.yaml array is following

a_hiera_hash:
    a_hiera_key:
        - item_dc1


Then, a_hiera_key will be merge as below.

hiera_lookup = hiera_hash('a_hiera_hash', {})
a_hiera_hash['a_hiera_key'] = [ 'item_one', 'item_two', 'item_three', 'item_dc1'] << this is what we will get

References:
https://github.com/puppetlabs/hiera (hiera)
https://docs.puppetlabs.com/hiera/1/lookup_types.html (hiera_hash)
https://docs.puppetlabs.com/references/latest/function.html (split)
https://forge.puppetlabs.com/puppetlabs/stdlib/readme (join)