ansible.builtin.constructed – Uses Jinja2 to construct vars and groups based on existing inventory.

Note

This inventory plugin is part of ansible-core and included in all Ansible installations. In most cases, you can use the short plugin name constructed even without specifying the collections: keyword. However, we recommend you use the FQCN for easy linking to the plugin documentation and to avoid conflicting with other collections that may have the same inventory plugin name.

New in version 2.4: of ansible.builtin

Synopsis

  • Uses a YAML configuration file with a valid YAML or .config extension to define var expressions and group conditionals

  • The Jinja2 conditionals that qualify a host for membership.

  • The Jinja2 expressions are calculated and assigned to the variables

  • Only variables already available from previous inventories or the fact cache can be used for templating.

  • When strict is False, failed expressions will be ignored (assumes vars were missing).

Parameters

Parameter

Comments

compose

dictionary

Create vars from jinja2 expressions.

Default: {}

groups

dictionary

Add hosts to group based on Jinja2 conditionals.

Default: {}

keyed_groups

list / elements=string

Add hosts to group based on the values of a variable.

Default: []

leading_separator

boolean

added in 2.11 of ansible.builtin

Use in conjunction with keyed_groups.

By default, a keyed group that does not have a prefix or a separator provided will have a name that starts with an underscore.

This is because the default prefix is “” and the default separator is “_”.

Set this option to False to omit the leading underscore (or other separator) if no prefix is given.

If the group name is derived from a mapping the separator is still used to concatenate the items.

To not use a separator in the group name at all, set the separator for the keyed group to an empty string instead.

Choices:

  • no

  • yes ← (default)

plugin

string / required

token that ensures this is a source file for the ‘constructed’ plugin.

Choices:

  • constructed

strict

boolean

If yes make invalid entries a fatal error, otherwise skip and continue.

Since it is possible to use facts in the expressions they might not always be available and we ignore those errors by default.

Choices:

  • no ← (default)

  • yes

use_extra_vars

boolean

added in 2.11 of ansible.builtin

Merge extra vars into the available variables for composition (highest precedence).

Choices:

  • no ← (default)

  • yes

Configuration:

  • INI entry:

    [inventory_plugins]
use_extra_vars = no

  • Environment variable: ANSIBLE_INVENTORY_USE_EXTRA_VARS

use_vars_plugins

boolean

added in 2.11 of ansible.builtin

Normally, for performance reasons, vars plugins get executed after the inventory sources complete the base inventory, this option allows for getting vars related to hosts/groups from those plugins.

The host_group_vars (enabled by default) ‘vars plugin’ is the one responsible for reading host_vars/ and group_vars/ directories.

This will execute all vars plugins, even those that are not supposed to execute at the ‘inventory’ stage. See vars plugins docs for details on ‘stage’.

Choices:

  • no ← (default)

  • yes

Examples

# inventory.config file in YAML format
plugin: constructed
strict: False
compose:
    var_sum: var1 + var2

    # this variable will only be set if I have a persistent fact cache enabled (and have non expired facts)
    # `strict: False` will skip this instead of producing an error if it is missing facts.
    server_type: "ansible_hostname | regex_replace ('(.{6})(.{2}).*', '\\2')"
groups:
    # simple name matching
    webservers: inventory_hostname.startswith('web')

    # using ec2 'tags' (assumes aws inventory)
    development: "'devel' in (ec2_tags|list)"

    # using other host properties populated in inventory
    private_only: not (public_dns_name is defined or ip_address is defined)

    # complex group membership
    multi_group: (group_names | intersect(['alpha', 'beta', 'omega'])) | length >= 2

keyed_groups:
    # this creates a group per distro (distro_CentOS, distro_Debian) and assigns the hosts that have matching values to it,
    # using the default separator "_"
    - prefix: distro
      key: ansible_distribution

    # the following examples assume the first inventory is from the `aws_ec2` plugin
    # this creates a group per ec2 architecture and assign hosts to the matching ones (arch_x86_64, arch_sparc, etc)
    - prefix: arch
      key: architecture

    # this creates a group per ec2 region like "us_west_1"
    - prefix: ""
      separator: ""
      key: placement.region

    # this creates a common parent group for all ec2 availability zones
    - key: placement.availability_zone
      parent_group: all_ec2_zones