Convert the DPK to use Hiera Hash Merging

The way PeopleSoft delivers Puppet and the Hiera backend, is that everything you define in psft_customizations.yaml overrides configuration defined elsewhere. This is a useful setup when getting started with the DPK and Puppet. But when using YAML files to manage your configuration across multiple servers, you’ll quickly find that you are re-entering the same configuration in many files.

Hiera, the tool Puppet uses to read YAML files, has multiple ways to look up data. First, let’s cover what a YAML hash is. A hash is a key-value structure used in the DPK to store configuration. For example, this is the hash for PS_HOME information:

ps_home:
  db_type:    "%{hiera('db_platform')}"
  unicode_db: "%{hiera('unicode_db')}"
  location:   "%{hiera('ps_home_location')}"
  remove:     true

The main hash key is ps_home, and its value is all the configuration below it. The next level down has 4 keys with 4 corresponding values. The appserver_domain_list hash is a large one that contains all the configuration for one or more app server domains.

Under the delivered setup, if you want to change a value for a domain you need to copy the entire appserver_domain_list hash into your psft_customizations.yaml file and make the change. With Hiera hashing, you could define your domains in a file named appservers.yaml and any specific server changes can be defined in hostname.yaml. For example, the hostname.yaml file could contain this hash to override a configuration:

appserver_domain_list:
  DEV:
    feature_settings:
      SERVER_EVENTS: "Yes"
      DOMAIN_GW:     "Yes"

This provides far more flexibility when working with YAML files, but it does introduce some complexity. If you want to give this a try, here is how you can convert the current DPK to use Hiera hasing.

Find/Replace

I used VisualStudio Code to do the find/replace. Open up the etc\modules directory and do these against the modules\pt_profile folder:

  • Find: hiera('tns_admin_list
  • Replace: hiera_hash('tns_admin_list

I repeated this step for the following lookups.

  • tns_admin_list
  • appserver_domain_list
  • prcs_domain_list
  • pia_domain_list

You don’t want to replace all the lookups – that will cause errors. But, you can replace additional lookups if you want. Anything that is a hash in YAML files can use the hiera_hash() lookup function. If you wanted to make the ps_home: key support hash merging, you could replace hiera('ps_home with hiera_hash('ps_home.

Change the Hiera Merge Behavior

By default, Hiera will look at the top-level keys of a hash and not merge the underlying settings. Hiera hashing will merge all the values inside the hash. This means you can you define a hash with default settings in a common file (e.g, default app server settings). Then you can specify server or application specific settings in a YAML file for that domain or server.

To enable the hash merging, open the hiera.yaml file under c:\programdata\puppetlabs\hiera\etc.

Add this line to the file:

:merge_behavior: deeper

Hiera Lookup Order

With Hiera hash merging, we can utilize more than the psft_customizations.yaml file to manage our configuration. We can use multiple YAML files to control our configuration. For example, we could have:

  • [hostname].yaml
  • dev.yaml
  • hr.yaml
  • common.yaml

So, this setup would let us define common configuration that is shared across all applications in the common.yaml. Next, we could define anything related to servers that run HR applications in the hr.yaml. For any settings that are specific to the Development region, we can add them into dev.yaml. Last, for anything that is specific to the server, we can add into the [hostname].yaml file. This setup would let you re-use the common, hr, and dev YAML files across multiple servers, and anything specific to the server would be defined in [hostname].yaml.

In the hiera.yaml file, we can define this setup like this:

:hierarchy:
  - "%{::hostname}"
  - dev
  - hr
  - common

Test Hiera Hashing

On the command line, you can use the hiera utility to test lookups with Hiera. To do a normal Hiera lookup, use

hiera appserver_domain_list

To test a hiera hash lookup, use

hiera --hash appserver_domain_list

If you have multiple YAML files with the appserver_domain_list hash, the first option will only show you the results from the top of the list. The second test should show you a merged appserver_domain_list hash.

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