Configuring Hiera

The Hiera configuration file is called hiera.yaml. It configures the hierarchy for a given layer of data.

Location of hiera.yaml files

There are several hiera.yaml files in a typical deployment. Hiera uses three layers of configuration, and the module and environment layers typically have multiple instances.

The configuration file locations for each layer:

Layer Location Example
Global $confdir/hiera.yaml /etc/puppetlabs/puppet/hiera.yaml C:\ProgramData\PuppetLabs\puppet\etc\hiera.yaml
Environment <ENVIRONMENT>/hiera.yaml /etc/puppetlabs/code/environments/production/hiera.yaml C:\ProgramData\PuppetLabs\code\environments\production\hiera.yaml
Module <MODULE>/hiera.yaml /etc/puppetlabs/code/environments/production/modules/ntp/hiera.yaml C:\ProgramData\PuppetLabs\code\environments\production\modules\ntp\hiera.yaml
Note: To change the location for the global layer’s hiera.yaml set the hiera_config setting in your puppet.conf file.

Hiera searches for data in the following order: global → environment → module. For more information, see Hiera configuration layers.

Related topics: codedir, Environments, Modules fundamentals.

Config file syntax

The hiera.yaml file is a YAML file, containing a hash with up to four top-level keys.

The following keys are in a hiera.yaml file:

  • version - Required. Must be the number 5, with no quotes.
  • defaults - A hash, which can set a default datadir, backend, and options for hierarchy levels.
  • hierarchy - An array of hashes, which configures the levels of the hierarchy.
  • default_hierarchy - An array of hashes, which sets a default hierarchy to be used only if the normal hierarchy entries do not result in a value. Only allowed in a module's hiera.yaml. 
version: 5
defaults:  # Used for any hierarchy level that omits these keys.
  datadir: data         # This path is relative to hiera.yaml's directory.
  data_hash: yaml_data  # Use the built-in YAML backend.

hierarchy:
  - name: "Per-node data"                   # Human-readable name.
    path: "nodes/%{trusted.certname}.yaml"  # File path, relative to datadir.
                                   # ^^^ IMPORTANT: include the file extension!

  - name: "Per-datacenter business group data" # Uses custom facts.
    path: "location/%{facts.whereami}/%{facts.group}.yaml"

  - name: "Global business group data"
    path: "groups/%{facts.group}.yaml"

  - name: "Per-datacenter secret data (encrypted)"
    lookup_key: eyaml_lookup_key   # Uses non-default backend.
    path: "secrets/nodes/%{trusted.certname}.eyaml"
    options:
      pkcs7_private_key: /etc/puppetlabs/puppet/eyaml/private_key.pkcs7.pem
      pkcs7_public_key:  /etc/puppetlabs/puppet/eyaml/public_key.pkcs7.pem

  - name: "Per-OS defaults"
    path: "os/%{facts.os.family}.yaml"

  - name: "Common data"
    path: "common.yaml"
Note: When writing in Hiera YAML files, do not use hard tabs for indentation.

The default configuration

If you omit the hierarchy or defaults keys, Hiera uses the following default values.
version: 5
hierarchy:
  - name: Common
    path: common.yaml
defaults:
  data_hash: yaml_data
  datadir: data
These defaults are only used if the file is present and specifies version: 5. If hiera.yaml is absent, it disables Hiera for that layer. If it specifies a different version, different defaults apply.

The defaults key

The defaults key sets default values for the lookup function and datadir keys, which lets you omit those keys in your hierarchy levels. The value of defaults must be a hash, which can have up to three keys: datadir, options, and one of the mutually exclusive lookup function keys.

datadir: a default value for datadir, used for any file-based hierarchy level that doesn't specify its own. If not given, the datadir is the directory data in the same directory as the hiera.yaml configuration file.

options: a default value for options, used for any hierarchy level that does not specify its own.

The lookup function keys: used for any hierarchy level that doesn't specify its own. This must be one of:

  • data_hash - produces a hash of key-value pairs (typically from a data file)
  • lookup_key - produces values key by key (typically for a custom data provider)
  • data_dig - produces values key by key (for a more advanced data provider)
  • hiera3_backend - a data provider that calls out to a legacy Hiera 3 backend (global layer only).

For the built-in data providers — YAML, JSON, and HOCON — the key is always data_hash and the value is one of yaml_data, json_data, or hocon_data. To set a custom data provider as the default, see the data provider documentation. Whichever key you use, the value must be the name of the custom Puppet function that implements the lookup function.

The hierarchy key

The hierarchy key configures the levels of the hierarchy. The value of hierarchy must be an array of hashes.

Indent the hash's keys by four spaces, so they line up with the first key. Put an empty line between hashes, to visually distinguish them. For example:

hierarchy:
  - name: "Per-node data"
    path: "nodes/%{trusted.certname}.yaml"

  - name: "Per-datacenter business group data"
    path: "location/%{facts.whereami}/%{facts.group}.yaml"

The default_hierarchy key

The default_hierarchy key is a top-level key. It is initiated when, and only when, the lookup in the regular hierarchy does not find a value. Within this default hierarchy, the normal merging rules apply. The default_hierarchy is not permitted in environment or global layers.

If lookup_options is used, the values found in the regular hierarchy have no effect on the values found in the default_hierarchy, and vice versa. A merge parameter, given in a call to lookup, is only used in the regular hierarchy. It does not affect how a value in the default hierarchy is assembled. The only way to influence that, is to use lookup_options, found in the default hierarchy.

For more information about the YAML file, see YAML.

Configuring a hierarchy level: built-in backends

Hiera has three built-in backends: YAML, JSON, and HOCON. All of these use files as data sources.

You can use any combination of these backends in a hierarchy, and can also combine them with custom backends. But if most of your data is in one file format, set default values for the datadir and data_hash keys.

Each YAML/JSON/HOCON hierarchy level needs the following keys:

  • name — A name for this level, shown in debug messages and --explain output.
  • path, paths, glob, globs, or mapped_paths (choose one) — The data files to use for this hierarchy level.
    • These paths are relative to the datadir, they support variable interpolation, and they require a file extension. See “Specifying file paths” for more details.
    • mapped_paths does not support glob expansion.
  • data_hash — Which backend to use. Can be omitted if you set a default. The value must be one of the following:
    • yaml_data for YAML.
    • json_data for JSON.
    • hocon_data for HOCON.
  • datadir — The directory where data files are kept. Can be omitted if you set a default.
    • This path is relative to hiera.yaml's directory: if the config file is at /etc/puppetlabs/code/environments/production/hiera.yaml and the datadir is set to data, the full path to the data directory is /etc/puppetlabs/code/environments/production/data.
    • In the global layer, you can optionally set the datadir to an absolute path; in the other layers, it must always be relative.
    • datadir supports variable interpolation.

For more information on built-in backends, see YAML, JSON, HOCON.

Specifying file paths

Options for specifying a file path.

Key Data type Expected value
path String One file path.
paths Array Any number of file paths. This acts like a sub-hierarchy: if multiple files exist, Hiera searches all of them, in the order in which they're written.
glob String One shell-like glob pattern, which might match any number of files. If multiple files are found, Hiera searches all of them in alphanumerical order.
globs Array Any number of shell-like glob patterns. If multiple files are found, Hiera searches all of them in alphanumerical order (ignoring the order of the globs).
mapped_paths Array or Hash A fact that is a collection (array or hash) of values. Hiera expands these values to produce an array of paths.
Note: You can only use one of these keys in a given hierarchy level.

Explicit file extensions are required, for example, common.yaml, not common.

File paths are relative to the datadir: if the full datadir is /etc/puppetlabs/code/environments/production/data and the file path is set to "nodes/%{trusted.certname}.yaml", the full path to the file is /etc/puppetlabs/code/environments/production/data/nodes/<NODE NAME>.yaml.

Note: Hierarchy levels should interpolate variables into the path.

Globs are implemented with Ruby's Dir.glob method:

  • One asterisk (*) matches a run of characters.
  • Two asterisks (**) matches any depth of nested directories.
  • A question mark (?) matches one character.
  • Comma-separated lists in curly braces ({one,two}) match any option in the list.
  • Sets of characters in square brackets ([abcd]) match any character in the set.
  • A backslash (\) escapes special characters.

Example:

- name: "Domain or network segment"
    glob: "network/**/{%{facts.networking.domain},%{facts.networking.interfaces.en0.bindings.0.network}}.yaml"

The mapped_paths key must contain three string elements, in the following order:

  • A scope variable that points to a collection of strings.
  • The variable name that is mapped to each element of the collection.
  • A template where that variable can be used in interpolation expressions.

For example, a fact named $services contains the array ["a", "b", "c"]. The following configuration has the same results as if paths had been specified to be [service/a/common.yaml, service/b/common.yaml, service/c/common.yaml].

- name: Example
    mapped_paths: [services, tmp, "service/%{tmp}/common.yaml"]

Configuring a hierarchy level: hiera-eyaml

Hiera 5 ( Puppet 4.9.3 and later) includes a native interface for the Hiera eyaml extension, which keeps data encrypted on disk but lets Puppet read it during catalog compilation.

To learn how to create keys and edit encrypted files, see the Hiera eyaml documentation.

Within hiera.yaml, the eyaml backend resembles the standard built-in backends, with a few differences: it uses lookup_key instead of data_hash, and requires an options key to locate decryption keys. Note that the eyaml backend can read regular yaml files as well as yaml files with encrypted data.

Important: To use the eyaml backend, you must have the hiera-eyaml gem installed where Puppet can use it. It's included in Puppet Server since version 5.2.0, so you just need to make it available for command line usage. To enable eyaml on the command line and with puppet apply, use sudo /opt/puppetlabs/puppet/bin/gem install hiera-eyaml.
Each eyaml hierarchy level needs the following keys:
  • name — A name for this level, shown in debug messages and --explain output.
  • lookup_key — Which backend to use. The value must be eyaml_lookup_key. Use this instead of the data_hash setting.
  • path, paths, mapped_paths, glob, or globs (choose one) — The data files to use for this hierarchy level. These paths are relative to the datadir, they support variable interpolation, and they require a file extension. In this case, you'll usually use .eyaml. They work the same way they do for the standard backends.
  • datadir — The directory where data files are kept. Can be omitted if you set a default. Works the same way it does for the standard backends.
  • options — A hash of options specific to hiera-eyaml, mostly used to configure decryption. For the default encryption method, this hash must have the following keys:
    • pkcs7_private_key — The location of the PKCS7 private key to use.
    • pkcs7_public_key — The location of the PKCS7 public key to use.
    • If you use an alternate encryption plugin, search the plugin's docs for the encryption options. Set an encrypt_method option, plus some plugin-specific options to replace the pkcs7 ones.
    • You can use normal strings as keys in this hash; you don't need to use symbols.

The file path key and the options key both support variable interpolation.

An example hierarchy level:

hierarchy:
  - name: "Per-datacenter secret data (encrypted)"
    lookup_key: eyaml_lookup_key
    path: "secrets/%{facts.whereami}.eyaml"
    options:
      pkcs7_private_key: /etc/puppetlabs/puppet/eyaml/private_key.pkcs7.pem
      pkcs7_public_key:  /etc/puppetlabs/puppet/eyaml/public_key.pkcs7.pem

Configuring a hierarchy level: legacy Hiera 3 backends

If you rely on custom data backends designed for Hiera 3, you can use them in your global hierarchy. They are not supported at the environment or module layers.

Note: This feature is a temporary measure to let you start using new features while waiting for backend updates.
Each legacy hierarchy level needs the following keys:
  • name — A name for this level, shown in debug messages and --explain output.
  • path or paths (choose one) — The data files to use for this hierarchy level.
    • For file-based backends, include the file extension, even though you would have omitted it in the v3 hiera.yaml file.
    • For non-file backends, don't use a file extension.
  • hiera3_backend — The legacy backend to use. This is the same name you'd use in the v3 config file's :backends key.
  • datadir — The directory where data files are kept. Set this only if your backend required a :datadir setting in its backend-specific options.
    • This path is relative to hiera.yaml's directory: if the config file is at /etc/puppetlabs/code/environments/production/hiera.yaml and the datadir is set to data, the full path to the data directory is /etc/puppetlabs/code/environments/production/data. Note that Hiera v3 uses 'hieradata' instead of 'data'.
    • In the global layer, you can optionally set the datadir to an absolute path.
  • options — A hash, with any backend-specific options (other than datadir) required by your backend. In the v3 config, this would have been in a top-level key named after the backend. You can use normal strings as keys. Hiera converts them to symbols for the backend.
The following example shows roughly equivalent v3 and v5 hiera.yaml files using legacy backends:
# hiera.yaml v3
---
:backends:
  - mongodb
  - xml

:mongodb:
  :connections:
    :dbname: hdata
    :collection: config
    :host: localhost

:xml:
  :datadir: /some/other/dir

:hierarchy:
  - "%{trusted.certname}"
  - "common"


# hiera.yaml v5
---
version: 5
hierarchy:
  - name: MongoDB
    hiera3_backend: mongodb
    paths:
      - "%{trusted.certname}"
      - common
    options:
      connections:
        dbname: hdata
        collection: config
        host: localhost

  - name: Data in XML
    hiera3_backend: xml
    datadir: /some/other/dir
    paths:
      - "%{trusted.certname}.xml"
      - common.xml

Configuring a hierarchy level: general format

Hiera supports custom backends.

Each hierarchy level is represented by a hash which needs the following keys:

  • name — A name for this level, shown in debug messages and --explain output.
  • A backend key, which must be one of:
    • data_hash
    • lookup_key
    • data_dig — a more specialized form of lookup_key, suitable when the backend is for a database. data_dig resolves dot separated keys, whereas lookup_key does not.
    • hiera3_backend (global layer only)
  • A path or URI key — only if required by the backend. These keys support variable interpolation. The following path/URI keys are available:
    • path
    • paths
    • mapped_paths
    • glob
    • globs
    • uri
    • uris - these paths or URIs work the same way they do for the built-in backends. Hiera handles the work of locating files, so any backend that supports path automatically supports paths, glob, and globs. uri (string) and uris (array) can represent any kind of data source. Hiera does not ensure URIs are resolvable before calling the backend, and does not need to understand any given URI schema. A backend can omit the path/URI key, and rely wholly on the options key to locate its data.
  • datadir — The directory where data files are kept: the path is relative to hiera.yaml's directory. Only required if the backend uses the path(s) and glob(s) keys, and can be omitted if you set a default.
  • options — A hash of extra options for the backend; for example, database credentials or the location of a decryption key. All values in the options hash support variable interpolation.

Whichever key you use, the value must be the name of a function that implements the backend API. Note that the choice here is made by the implementer of the particular backend, not the user.

For more information, see custom Puppet function.