Ansible - Variable precedence fails when hosts are the same - ansible

Question

I want to make the most of variable precedence with ansible.
So let’s have a look at this simplified project:
├── group_vars
│ └── all
│ └── web
├── hosts
│ └── local
└── site.yml
The inventory file hosts/local:
[local_web]
192.168.1.20
[local_db]
192.168.1.20
[web:children]
local_web
[db:children]
local_db
The group_vars/all file:
test: ALL
The group_vars/web file:
test: WEB
The site.yml file:
---
- name: Test
hosts: db
tasks:
- debug: var=test
Alright, so this is just to test variable precedence. As I run ansible in the db group, the test variable should display “ALL”, as ansible will only looks into group_vars/all, right?
Wrong:
TASK: [debug var=test] ********************************************************
ok: [192.168.1.20] => {
"var": {
"test": "WEB"
}
}
Actually, if local_web and local_db hosts are different, then it works.
Why ansible still looks into an unrelated config file when hosts are the same? Is that a bug or just me?

Answer 1

You're stating that 192.168.1.20 is a member of all 4 of your defined groups, and that's independent of how you reference the host in your playbook. No matter how you reference the host in your playbook Ansible is going to evaluate all the groups that host is in and import variables based on those groups.
Here's a handy test to demonstrate this:
- name: Test
hosts: db
tasks:
- debug: msg="{{ inventory_hostname }} is in group {{ item }}"
when: inventory_hostname in groups[item]
with_items: group_names
The output of this is:
TASK: [debug msg="host is in group {{ item }}"] *******************************
ok: [192.168.1.20] => (item=db) => {
"item": "db",
"msg": "192.168.1.20 is in group db"
}
ok: [192.168.1.20] => (item=local_db) => {
"item": "local_db",
"msg": "192.168.1.20 is in group local_db"
}
ok: [192.168.1.20] => (item=local_web) => {
"item": "local_web",
"msg": "192.168.1.20 is in group local_web"
}
ok: [192.168.1.20] => (item=web) => {
"item": "web",
"msg": "192.168.1.20 is in group web"
}
Since the host is in the web group then the web group_vars file was included.

Answer 2

#Bruce P answer is right.
However, this ansible behavior is not satisfying for me, because it change variable precedence depending on the hosts. Instead of group_vars, I use the vars_files dict.
I moved group_vars into a directory named vars.
The updated site.yml:
---
- name: Test
hosts: db
tasks:
- debug: var=test
vars_files:
- vars/all
- vars/db
Now, test displays “ALL”, as I wanted. It first read vars/all, then vars/db (which is empty).
(Note: variable precedence seems to be a bit buggy at the moment - v1.9.2 -. This means if you use variables as var files name, ansible will not load files in the order expected.)

Answer 3

Another solution that can leave variables in group_vars is to replace the inventory file hosts/local by two files : hosts/inv_db and hosts/inv_web, and to use the -i option to specify the inventory file to use.