Expressions are not evaluated in the nested ansible variables - ansible

Question

$ ls play.d/roles/debug/*
play.d/roles/debug/tasks:
main.yml
play.d/roles/debug/vars:
main.yml
$ cat play.d/roles/debug/tasks/main.yml
- debug: msg="{{ name }}"
- debug: msg="{{ vars[name]['test_var'] }}"
- debug: msg="{{ vars['nested_var']['test_var'] }}"
- debug: msg="{{ test_var }}"
$ cat play.d/roles/debug/vars/main.yml
test_var: "{{ 'value-1' if cpu == 'x64' else 'value-2' }}"
nested_var:
test_var: "{{ 'value-1' if cpu == 'x64' else 'value-2' }}"
$ cat play.d/debug.yml
- hosts: all
gather_facts: yes
roles:
- debug
$ cat inv.d/inv
[all:vars]
cpu = 'x64'
[test-srv]
52.19.xxx.xxx
With this pretty straightforward setup I expect that Ansible should evaluate inline conditionals regardless of their position (top level or nested). However it seems, that nested variables become literal strings of the expressions:
# ansible-playbook -i inv.d/inv play.d/debug.yml -e name=nested_var -l test-srv
PLAY [all] ********************************************************************
GATHERING FACTS ***************************************************************
ok: [52.19.xxx.xxx]
TASK: [debug | debug msg="{{ name }}"] ****************************************
ok: [52.19.xxx.xxx] => {
"msg": "nested_var"
}
TASK: [debug | debug msg="{{ vars[name]['test_var'] }}"] **********************
ok: [52.19.xxx.xxx] => {
"msg": "{{'value-1' if cpu == 'x64' else 'value-2'}}"
}
TASK: [debug | debug msg="{{ vars['nested_var']['test_var'] }}"] **************
ok: [52.19.xxx.xxx] => {
"msg": "{{'value-1' if cpu == 'x64' else 'value-2'}}"
}
TASK: [debug | debug msg="{{ 'value-1' if cpu == 'x64' else 'value-2' }}"] ****
ok: [52.19.xxx.xxx] => {
"msg": "value-1"
}
PLAY RECAP ********************************************************************
52.19.xxx.xxx : ok=5 changed=0 unreachable=0 failed=0
Who's doing it wrong, me or Ansible? Any ideas?
# ansible --version
ansible 1.9.2

Answer 1

I'm not sure what do you try to achieve, but you exploit an undocumented way of accessing variables via vars hash.
And this vars hash is special in a way that Ansible template engine will not template it, but return it's value as is.
For Ansible 2.x it's described here.
So in case of {{ vars[name]['test_var'] }} it will resolve name->'nested_var' first but will not then resolve vars['nested_var']['test_var'] and return it as literal string.
If your variables are defined as host facts (inventory-host/group variables, dynamic facts set by set_fact), you can access host_vars magic variable like host_vars[inventory_hostname][dynamic_name]['subelement'] to access variable dynamically.
If your variables are play/role bound, like in your case, I can suggest to use root-hash with predefined name, like:
known_name:
nested_var: # this key name is known known in advance
subelement: "{{ 'value-1' if cpu == 'x64' else 'value-2' }}"
Here you can access dynamic element by known_name[dynamic_name]['subelement'].