---
date: 2013-04-11
title: Using Hiera with Puppet
category:   devops
---

Using Hiera with Puppet is something I have struggled with a bit. I
could see the benefits, namely decoupling my site configuration from my
logic. However, for some reason I struggled a bit to really get my head
around it. This was compounded by it being quite new (only really
integrated in Puppet 3), so the docs are little lacking.

There is some though, the [documentation on PuppetLab's
site](https://docs.puppetlabs.com/hiera/latest/) is excellent, but a bit
light. It explains the principles well, but is a little limited in
real-world examples. Probably the best resource I found was Kelsey
Hightower's excellent presentation at [PuppetConf
2012](https://youtu.be/z9TK-gUNFHk):

I learnt a lot from that, but it would be nice if there was an
equivalent written down. I suppose that is what I am aiming at here.

Configuration
-------------

-   [NFS Module](https://github.com/chriscowley/puppet-nfs)
-   [Hiera
    Config](https://github.com/chriscowley/my-master-puppet/blob/master/hiera.yaml)
-   [Hiera
    Data](https://github.com/chriscowley/my-master-puppet/tree/master/hieradata)

I am using Open Source Puppet 3. If you are using 2.7 or Puppet
Enterprise, files will be in a slightly different place. That is all
explained in the documentation linked above.

The first thing you need to do is configure Hiera using the file
`/etc/puppet/hiera.yaml`. Mine looks like this:

    ---
    :backends:
    - yaml
    :yaml:
    :datadir: /etc/puppet/hieradata/
    :hierarchy:
    - %{::clientcert}
    - common

This tells Hiera to use only the YAML backend - I do not like JSON
because it always looks messy to me. It will look for the data in the
folder `/etc/puppet/hieradata`. Finally it will look in that folder for
a file called .yaml, then common.yaml. The process it uses to apply the
values is explained very nicely in this image: {% img
<https://docs.puppetlabs.com/hiera/latest/images/hierarchy1.png> %}

Next, create the file `/etc/puppet/hieradata/<certname>.yaml` that
contains your NFS exports:

    ---
    exports:
    - /srv/iso
    - /srv/images

Now, checkout my NFS module from Github links above. If you are not on
RHEL6 or similar (I use Centos personally) you will have to modify it as
needed.

There are 2 files that are really interesting here. The manifest file
(manifests/server.pp) and the template to build the `/etc/exports` file
(templates/exports.erb). We'll take apart the manifest, the template
just iterates over the data passed to it from that.

The first line creates an array variable called \$exports from the Hiera
data. Specifically, it looks for a key called *exports*. Hiera then goes
through the hierarchy explained earlier looking for that key. In this
case it will find it in the .yaml.

This data is now used for 2 things. First it creates the necessary
folders, then it build `/etc/exports`. Here there is a minor problem,
because you cannot do a *for each* loop in a Puppet manifest. We can
fiddle it a bit by using a [defined
type](https://docs.puppetlabs.com/puppet/3/reference/lang_defined_types.html).

The line `list_exports { $exports:; }` passes the `$exports` array to
the type we define above it. This then goes ahead and creates the
folders ready to be exported. The `->` builds an [order
relationship](https://docs.puppetlabs.com/puppet/3/reference/lang_relationships.html#chaining-arrows)
with the File resource for */etc/exports*. Specifically, that the
directories need to be created before they are exported.

    define list_exports {
      $export = $name
      file { $export:
        ensure => directory,
        mode => '0755',
        owner => 'root',
        group => 'root'
      }
    }
    list_exports { $exports:; } -> File['/etc/exports']

Now it can go ahead and build the `/etc/exports` file using that same
\$exports array in the `templates/exports.erb` template:

    <% [exports].flatten.each do |export| -%>
    <%= export %> 192.168.1.0/255.255.255.0(rw,no_root_squash,no_subtree_check)
    <% end -%>

There is nothing especially Hiera'y about this, other than where the
data in that array came from.

The rest of the manifest deals with installing the packages and
configuring services. Once again, nothing especially linked with Hiera,
but hopefully it will be useful for anyone wanting to Puppetize their
NFS servers - which of course you should be.