Ansible - read inventory hosts and variables to group_vars/all file

Question

I have a dummy doubt that keeps me stuck for a long time. I have a very banal inventory file with hosts and variables:

[lb]
10.112.84.122

[tomcat]
10.112.84.124

[jboss5]
10.112.84.122

...

[tests:children]
lb
tomcat
jboss5

[default:children]
tests

[tests:vars]
data_base_user=NETWIN-4.3
data_base_password=NETWIN
data_base_encrypted_password=
data_base_host=10.112.69.48
data_base_port=1521
data_base_service=ssdenwdb
data_base_url=jdbc:oracle:thin:@10.112.69.48:1521/ssdenwdb

The problem is that I need to access all these hosts and variables, in the inventory file, from the group_vars/all file.

I've tried the following manners to access the host IP:

{{ lb }}
"{{ hostvars[lb] }}"
"{{ hostvars['lb'] }}"
{{ hostvars[lb] }}

To access a host variable I tried:

"{{ hostvars[tests].['data_base_host'] }}"

All of them are wrong!!! Can anyone help me find out the best practice to access hosts and variables, not from a playbook but from a variables file?

EDIT:

Ok. Let's clarify.

Problem: Use a host declared in the inventory file in a variable file, let's say: group_vars/all.

Example: I have a DB host with IP:10.112.83.37.

Inventory file:

[db]
10.112.83.37

In the group:vars/all file I want to use that IP to build a variable.

group_vars/all file:

data_base_url=jdbc:oracle:thin:@{{ db }}:1521/ssdenwdb

In a template I use the variable built in the group_vars/all file.

Template file:

oracle_url = {{ data_base_url }}

The problem is that the {{ db }} variable in the group_vars/all file is not replaced by the DB host IP. The user can only edit the inventory file.

Answer 1

- name: host
   debug: msg="{{ item }}" 
   with_items:
    - "{{ groups['tests'] }}"

This piece of code will give the message:

'10.112.84.122'
'10.112.84.124'

as groups['tests'] basically return a list of unique ip addresses ['10.112.84.122','10.112.84.124'] whereas groups['tomcat'][0] returns 10.112.84.124.