The tale of Ansible and the variable that should be there but isn't

NoneTypeAndAAnsibleMapping.md

The tale of Ansible and the variable that should be there but isn't

So I had a role where I needed to define lots of variables. I decided to split them over multiple files like this:

my_app/defaults/main/
  main.yml
  another.yml 
  yet_another.yml

Tinkering with my shiny new role I moved all of the variables from yet_another.yml to group_vars. Being cautious, I just commented them out.

I ran my role and got:

TASK [include_role : my_app]
***********************************************************************
ERROR! failed to combine variables, expected dicts but
got a 'NoneType' and a 'AnsibleMapping':
null

Trying to find out which of the variables caused the issue, I commented them out one by one. When I arrived at the last variable in the file, the role failed. Aha! Found the culprit. Or so I thought.

Then the search for the misspelled variable began. To no avail.

Okay, maybe the var does not properly get propagated from group_vars?

$ ansible-inventory --graph my_app --vars -i environments/mine/ | less
[...]
|  |--{my_app_default_permission = read-write}
|  |--{my_app_default_user_role = Super admin role}

Nope, it's right there, wether I comment out the variable or not, with the expected values. Hm.

1. Comment it out, and another variable back in. Role runs fine. What is worng here?

2. Add a variable that is used nowhere in the role instead, role runs fine. What?

    stupid_unused_var: nothing
   

3. move yet_another.yml to yet_another.yml.bak and the role runs. Waiiiit...

4. add a new variables file with nothing but --- and a comment: role fails.

Head -> Desk.

Lesson learned:

Variable files in default/main/whatever.yml need to contain more than just the three dashes declaring that this is a yaml file and a couple of comments.

---
# just a comment
# and nothing more

This will be interpreted as a null-value by Ansible (2.10 in my case), which will entail all sorts of weird errors, that are really not what they look like.