What is the proper way to check for required variables?

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1

I want to make my playbook in a way where process will fail with an error if user was not provided required parameters, what is the way to do that in Ansible?

2

The default behavior is to fail if using a variable that is not defined.
There is also a configuration option that disables this, and then you
can use "{{ myvar | mandatory }}" to explicitly have the same effect.
Keep in mind, though, that the failure occurs when reaching a task that
uses an undefined variable. If you want to fail before any task is
executed, you could add another task at the top of your tasks that fails
if a mandatory variable is not defined. For example:

tasks:
   - fail: msg="Variable '{{ item }}' is not defined"
     when: item not in hostvars[inventory_hostname]
     with_items:
       - myvariable1
       - myvariable2

3

- fail: msg="Bailing out. this play requires 'bar'"
      when: bar is not defined

my 2�

4

Thanks for the tips, didnt know about both!

What if I want to “declare” variables somewhere, to tell user about what he can use, but leave that variables “undefined” so they will fail is defined test? What people usually do in this situations?
I want to make file like required_vars.yml and put all required variables there, and then do something like this:

- name: check required variables
fail: msg="Variable '{{ item }}' is not defined"` `when: item is defined` with_items: - include: required_vars.yml`

Is there way to do this?

5

You can put in the required_vars.yml file: Then, in the playbook: Normally, you would also want to document the structure of your vars, so I would suggest you to write a ‘readme’ file with example definitions of the all possible variables, both mandatory and non-mandatory.

6

error_on_undefined_variables is the default in ansible.cfg

I STRONGLY recommend leaving that setting on.

Then the whole “|mandatory” thing is also not required.

It’s there because very old ansible didn’t require variables to be defined by default, now it does, so many upgraders may just wish to change the setting.

7

Hi Guys,

I am trying to force the ansible play to check againt the command line variable, here is my “check-requirement.yml” and required_var:

  • fail: msg=“Bailing out this play requires ‘{{ item }}’”
    when: item is not defined
    with_items: required_vars

I have set default/main.yml with following line:

required_vars:

  • env

Now when i run the play book without env, its skipping rather than failing: Please help me to fix this…

Here is the message:

root@test-server-s01:~/ranker-orchestration/roles# ansible-playbook tomcat-role-test.yml

PLAY [localhost] **************************************************************

GATHERING FACTS ***************************************************************
ok: [localhost]

TASK: [tomcat | fail msg=“Bailing out this play requires ‘{{ item }}’”] *******
skipping: [localhost] => (item=env)

TASK: [tomcat | Update apt cache] *********************************************
ok: [localhost]

TASK: [tomcat | Install Tomcat 7] *********************************************
ok: [localhost]

TASK: [tomcat | Configure tomcat memory/java_home configuration] **************
ok: [localhost]

TASK: [tomcat | Configure tomcat server configuration, port, connections ssl etc] ***
ok: [localhost]

PLAY RECAP ********************************************************************
localhost : ok=6 changed=0 unreachable=0 failed=0

8

"item" is a variable that is always defined when you use with_items.
Ansible will parse that and confirm it exists and is defined.

You could pass "item" through Jinja2 first, which will use the value
it's defined to and fail if it can't locate that variable.

when: "{{ item }} is not defined"

I haven't done a serious effort to understand the Ansible/Jinja2 flow
but the above should work.

Giovanni

9

Hello,

All my roles check mandatory vars before doing anything,
that way :

  • fail: msg=“Variable ‘{{ item }}’ is not defined”
    when: item not in vars
    with_items:
  • var1
  • vars_xx
  • vars3
10

Hi, You can try below solution to check all required parameter (the parameter user has to specify while running the playbook/script) 1. Your var file - required_vars.yml

required_vars:

  • var1

  • var2

  • var3

  1. In task, include your var file
  • include_vars: …/vars/required_vars.yml
  1. Task to validate parameters (can be written in separate yml file)