Debugging variables in Ansible

Sometimes it's useful to debug where and how your playbook variables are defined. Your variables might be returning unexpected values or variable precedence[1] is playing tricks on you.

This playbook shows how to use three hidden YAML attributes (_line_number, _column_number and _data_source)[2] to debug the origin of your playbook variables.

As an example we have defined the following variables in our example playbook debugging-variables.yml:

var1 is defined using the vars Play directive
var1 is also defined in the inventory.. Precendence ;-)
var2 is defined using the vars_files Play directive
var3 is defined in host_vars/localhost.yml
var4 is defined in group_vars/all.yml
var5 is defined using the include_vars module
var6 is defined in the inventory

References:
[1] Ansible Docs on variable precedence: http://docs.ansible.com/ansible/latest/user_guide/playbooks_variables.html#variable-precedence-where-should-i-put-a-variable
[2] Nitty gritty details on how these attributes are set inside Ansible: https://github.com/ansible/ansible/blob/devel/lib/ansible/parsing/yaml/objects.py.

Running the playbook

Use the ansible-playbook command to run the included playbook:

$ ansible-playbook debugging-variables.yml

Should result in the following:

ok: [localhost] => (item=var1) => {
    "item": "var1",
    "var1, var1.__dict__": "(u'value1', {'_column_number': 11, '_line_number': 9,
    '_data_source': u'/Dev/project/debugging-variables.yml'})"
}
...

Example usage

How to access these hidden variable attributes inside a playbook or template:

Variable 'var1' has the value '{{ var1 }}', as defined on line {{ var1._line_number }},
column {{ var1._column_number }} in '{{ var1._data_source }}'.

Which will return the following information:

Variable 'var1' has the value 'value1', as defined on line 9, column 11 in '/Dev/project/playbook.yml'.

Verify in /Dev/project/playbook.yml:

 7: 
 8:  vars:
 9:    var1: value1 <-- line 9
10:          ^-- column 11
11: