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chore(ansible): warn about variable precedence and imported tasks

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Michele Cereda
2025-08-09 16:26:07 +02:00
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@@ -430,6 +430,59 @@ The current hierarchy is as follows (from lowest to highest priority, with the l
1. Parameters from `import_tasks` and `include_tasks` statements.
1. Extra variables specified in the command line like `-e "user=my_user"`.
> [!warning]
> Values set in the `vars` key of `import_tasks` or `include_tasks` statements did **not** always override the ones
> configured in the `vars` key of imported tasks.<br/>
> While this _may_ very well be a skill issue of mine, one can get around this by setting defaults for modules in the
> modules' attributes themselves, e.g.:
>
> ```diff
> - name: Create an RDS DB instance
> - vars:
> - allow_major_version_upgrade: false
> - auto_minor_version_upgrade: true
> - availability_zone: eu-north-1a
> amazon.aws.rds_instance:
> - allow_major_version_upgrade: "{{ allow_major_version_upgrade }}"
> - auto_minor_version_upgrade: "{{ auto_minor_version_upgrade }}"
> - availability_zone: "{{ availability_zone }}"
> + allow_major_version_upgrade: "{{ allow_major_version_upgrade | default(false) | bool }}"
> + auto_minor_version_upgrade: "{{ auto_minor_version_upgrade | default(true) | bool }}"
> + availability_zone: "{{ availability_zone | default('eu-west-1b') }}"
> ```
Consider setting _private_ defaults when some variables depend on multiple other variables (e.g. abstractions), so tasks
can easily use or reference them, e.g.:
```yml
- name: Set 'private' defaults for other tasks to use
ansible.builtin.set_fact:
_db_instance_identifier: >-
{{
[
db_instance_identifier | default(None),
instance_identifier | default(None),
instance_id | default(None),
id | default(None),
] | select | first
}}
- name: Set 'private' defaults for only this task
vars:
_allocated_storage: "{{ allocated_storage | default(20) | int }}"
_master_username: &master_username >-
{{
[
master_username | default(None),
username | default(None),
] | select | first
}}
amazon.aws.rds_instance:
db_instance_identifier: "{{ _db_instance_identifier }}"
master_username: *master_username
allocated_storage: "{{ _allocated_storage }}"
max_allocated_storage: "{{ max_allocated_storage | default(_allocated_storage) }}"
```
## Templating
Ansible leverages [Jinja2 templating], which can be used directly in tasks or through the `template` module.