Ansible: Merge variable plugin

Use case

This plugin can be used to define a variable multiple times, either via host_vars, group_vars, inventory variables or other, and at runtime combine the variable values to have a single variable that can be used within a role. This is similar to how Salt allows its pillar data to be defined.

This works with both arrays, lists, and dictionaries in YAML

Configuration

Ansible should be configured to use a plugin directory that holds a copy of merge_variables.py

This can be done via ansible.cfg or using environment variables

Ansible documentation

Using the plugin

The plugin needs to be called as a task, provided with the variable name that needs to be merged:

- merge_variables:
    name: variable_name

The plugin will then look for any variable that matches either variable_name or starts with variable_name__ and will then start the merge process

Variables cannot be defined multiple times with the same name, Ansible will merge these before the plugin can access them

Example:

group_vars/all.yaml

variable_name:
  - a
  - b

host_vars/host.yaml

variable_name__host:
  - c
  - d

These will be merged and able to be used as variable_name within the role

variable_name:
  - a
  - b
  - c
  - d

Merge stratigies are available and work the same way as Salt

• overwrite
• first
• last
• remove

These can be used by defining a __ key at the start of the data.

Example:

group_vars/all.yaml

variable_name:
  - a
  - b

host_vars/host.yaml

variable_name__host:
  __: overwrite
  - c
  - d