I cannot find any where in the document about when the variable
substitution happen. I want to know this because we can define variables in
several places and we can refer to variables in different scopes. For
example, a group var or host var or even a extra var can refer to a
variable defined in roles. This is some kind of unexpected. Because there
is a variable override priority described here:
https://docs.ansible.com/ansible/latest/user_guide/playbooks_variables.html#understanding-variable-precedence
Normally we would thought the variable in higher priority get initialized
first and cannot refer to low priority variables (extra vars override group
vars, so normal people would expect we cannot refer to a group var in extra
var) but this is not true. Normally we can refer to a variable anywhere in
any scope. Even extra variable `-e testvar04='t
estvar03:{{testvar03}}'` can be expand in playbook. Here the testvar03 is
defined in group vars and refer to a variable only defined in role
defaults. So it looks like the variable substitution only happens at the
very end right before the variable is used in a task. However, when I try
to obtain variable in another host this rule is broken again: `
hostvars[ansible_host].testvar02` expands to `var_in_role: {{var_in_role}}`.
The var_in_role is defined in role vars. So I wonder what is the actual
rule about variable substitution? When the substitution actually happens?
Do we have any chapter in the document define this behaviour?
Here is any example:
we have project structure like following:
```
├── inventory
│ └── hosts.yml
├── roles
│ └── test_var_substitution
│ ├── defaults
│ │ └── main.yml
│ ├── tasks
│ │ └── main.yml
│ └── vars
│ └── main.yml
└── test_var_substitution.yml
```
hosts.yml
```yaml
all:
children:
local:
hosts:
localhost:
ansible_connection: local
hostname: localhost
host_var01: "define in host file"
host_var02: "group_local_var01: {{group_local_var01}}"
vars:
group_local_var01: "define in local group"
vars:
testvar01: "set in group"
testvar02: "var_in_role: {{var_in_role}}"
testvar03: "var_in_role_default: {{var_in_role_default}}"
```
`roles/test_var_substitution/defaults/main.yml`:
```yaml
var_in_role_default: "define in role default only"
```
`roles/test_var_substitution/vars/main.yml`:
```yaml
var_in_role: "define in role only"
```
`roles/test_var_substitution/tasks/main.yml`:
```yaml
- debug:
var: ansible_host
- name: show hostvars[ansible_host].testvar02
debug:
msg: "{{hostvars[ansible_host].testvar02}}"
- name: show hostvars[ansible_host].testvar03
debug:
msg: "{{hostvars[ansible_host].testvar03}}"
- name: show hostvars[hostname].host_var02
debug:
msg: "{{hostvars[hostname].host_var02}}"
- debug:
var: testvar01
- debug:
var: testvar02
- debug:
var: testvar03
- debug:
var: host_var02
```
`test_var_substitution.yml`:
```yaml
- hosts: all
connection: local
roles:
- test_var_substitution
tasks:
- debug:
var: testvar01
- debug:
var: testvar02
- debug:
var: testvar03
- debug:
var: testvar04
- debug:
var: hostvars[ansible_host].testvar02
```
```
$ ansible-playbook -i inventory test_var_substitution.yml -e
testvar04='testvar03:{{testvar03}}'
PLAY [all]
**************************************************************************************************
TASK [Gathering Facts]
**************************************************************************************
ok: [localhost]
TASK [test_var_substitution : debug]
************************************************************************
ok: [localhost] => {
"ansible_host": "localhost"
}
TASK [test_var_substitution : show hostvars[ansible_host].testvar02]
****************************************
ok: [localhost] => {
"msg": "var_in_role: {{var_in_role}}"
}
TASK [test_var_substitution : show hostvars[ansible_host].testvar03]
****************************************
ok: [localhost] => {
"msg": "var_in_role_default: {{var_in_role_default}}"
}
TASK [test_var_substitution : show hostvars[hostname].host_var02]
*******************************************
ok: [localhost] => {
"msg": "group_local_var01: define in local group"
}
TASK [test_var_substitution : debug]
************************************************************************
ok: [localhost] => {
"testvar01": "set in group"
}
TASK [test_var_substitution : debug]
************************************************************************
ok: [localhost] => {
"testvar02": "var_in_role: define in role only"
}
TASK [test_var_substitution : debug]
************************************************************************
ok: [localhost] => {
"testvar03": "var_in_role_default: define in role default only"
}
TASK [test_var_substitution : debug]
************************************************************************
ok: [localhost] => {
"host_var02": "group_local_var01: define in local group"
}
TASK [debug]
************************************************************************************************
ok: [localhost] => {
"testvar01": "set in group"
}
TASK [debug]
************************************************************************************************
ok: [localhost] => {
"testvar02": "var_in_role: define in role only"
}
TASK [debug]
************************************************************************************************
ok: [localhost] => {
"testvar03": "var_in_role_default: define in role default only"
}
TASK [debug]
************************************************************************************************
ok: [localhost] => {
"testvar04": "testvar03:var_in_role_default: define in role default
only"
}
TASK [debug]
************************************************************************************************
ok: [localhost] => {
"hostvars[ansible_host].testvar02": "var_in_role: {{var_in_role}}"
}
PLAY RECAP
**************************************************************************************************
localhost : ok=14 changed=0 unreachable=0
failed=0 skipped=0 rescued=0 ignored=0
```
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