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

Note

This module is part of ansible-core and included in all Ansible installations. In most cases, you can use the short module name constructed even without specifying the collections: keyword. However, we recommend you use the FQCN for easy linking to the module documentation and to avoid conflicting with other collections that may have the same module 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 Choices/Defaults Configuration Comments
compose
dictionary
Default:
{}
Create vars from jinja2 expressions.
groups
dictionary
Default:
{}
Add hosts to group based on Jinja2 conditionals.
keyed_groups
list / elements=string
Default:
[]
Add hosts to group based on the values of a variable.
leading_separator
boolean
added in 2.11 of ansible.builtin
    Choices:
  • no
  • yes ←
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.
plugin
string / required
    Choices:
  • constructed
token that ensures this is a source file for the 'constructed' plugin.
strict
boolean
    Choices:
  • no ←
  • yes
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.
use_extra_vars
boolean
added in 2.11 of ansible.builtin
    Choices:
  • no ←
  • yes
ini entries:

[inventory_plugins]
use_extra_vars = no

env:ANSIBLE_INVENTORY_USE_EXTRA_VARS
Merge extra vars into the available variables for composition (highest precedence).
use_vars_plugins
boolean
added in 2.11 of ansible.builtin
    Choices:
  • no ←
  • yes
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'.

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