How to Make Ansible variable mandatory - ansible

Question

I'm looking for the way how to make Ansible to analyze playbooks for required and mandatory variables before run playbook's execution like:
- name: create remote app directory hierarchy
file:
path: "/opt/{{ app_name | required }}/"
state: directory
owner: "{{ app_user | required }}"
group: "{{ app_user_group | required }}"
...
and rise error message if variable is undefined, like:
please set "app_name" variable before run (file XXX/main.yml:99)

Answer 1

As Arbab Nazar mentioned, you can use {{ variable | mandatory }} (see Forcing variables to be defined) inside Ansible task.
But I think it looks nicer to add this as first task, it checks is app_name, app_user and app_user_group exist:
- name: 'Check mandatory variables are defined'
assert:
that:
- app_name is defined
- app_user is defined
- app_user_group is defined

Answer 2

You can use this:
{{ variable | mandatory }}

Answer 3

Usually inside a role I perform checking input variables like in the example:
- name: "Verify that required string variables are defined"
assert:
that:
- "{{ ahs_var }} is defined"
- "{{ ahs_var }} | length > 0"
- "{{ ahs_var }} != None"
fail_msg: "{{ ahs_var }} needs to be set for the role to work"
success_msg: "Required variable {{ ahs_var }} is defined"
loop_control:
loop_var: ahs_var
with_items:
- ahs_item1
- ahs_item2
- ahs_item3
by the way there are some tricks:
Don't use global variables inside a role.
If you want use global variables define the role specific variable & set global variable to it i.e. some_role_name__db_port: "{{ db_port | default(5432) }}".
It makes sense to use role name as the prefix for variable. it helps to understand the source inventory easier.
Your role might be looped some how, so it makes sense to override the default item.

Answer 4

One way to check if mandatory variables are defined is:
- fail:
msg: "Variable '{{ item }}' is not defined"
when: item not in vars
with_items:
- app_nam
- var2

Answer 5

There are 2 approaches:
Specify |mandatory filter
Beware dictionaries - if a key with mandatory value fails to eval, you may have a hard time uh understanding which is it.
Use assert module

Answer 6

If using a role-based architecture, check out the docs on role argument validation.
It allows for you to specify a roles/<role_name>/meta/argument_specs.yml file which allows you to make variables required. Here is an example taken from their sample specification:
# roles/myapp/meta/argument_specs.yml
---
argument_specs:
# roles/myapp/tasks/main.yml entry point
main:
short_description: The main entry point for the myapp role.
options:
myapp_int:
type: "int"
required: false
default: 42
description: "The integer value, defaulting to 42."
myapp_str:
type: "str"
required: true
description: "The string value"
# roles/myapp/tasks/alternate.yml entry point
alternate:
short_description: The alternate entry point for the myapp role.
options:
myapp_int:
type: "int"
required: false
default: 1024
description: "The integer value, defaulting to 1024."