Mastering Ansible Playbook Variables: Priorities, Definitions, and Best Practices

Ansible Playbook Variables

1. Variable Priority

extra vars

(command line -e) – highest priority

Connection variables defined in inventory (e.g., ansible_ssh_user) – second priority

Other variables such as command‑line conversion, play variables, include variables, role variables – third priority

Variables defined directly in the inventory file – fourth priority

System‑discovered facts – fifth priority

Role default variables – lowest priority

Within the inventory list, a variable defined for a single host overrides a variable defined for a host group. The precedence order from high to low is: host_vars → inventory host variables → group_vars → inventory group variables.

1.1 YAML Pitfalls

When a value starts with {{ foo }} in YAML, the entire line must be quoted to avoid being interpreted as a dictionary.

|---
|---
|---
|hosts: app_servers
|vars:
|app_path: {{ base_path }}/data/web

Corrected version:

|---
|---
|---
|hosts: app_servers
|vars:
|app_path: "{{ base_path }}/data/web"

2. Ansible Playbook Variable Configuration Methods

2.1 Define Variables in the Inventory Host File

Variables can be placed directly in /etc/ansible/hosts and apply only to the specified host or group.

| $ egrep -v "^#|^$" /etc/ansible/hosts
| 10.4.7.101 key=20180101
| 10.4.7.102 key="niubility"
| $ cat ansi.yml
|---
|- hosts: all
|  gather_facts: False
|  tasks:
|   - name: haha
|     debug: msg="the {{ inventory_hostname }} value is {{ key }}"
| $ ansible-playbook ansi.yml
| PLAY [all]
| TASK [haha]
| ok: [10.4.7.101] => {"msg": "the 10.4.7.101 value is 20180101"}
| ok: [10.4.7.102] => {"msg": "the 10.4.7.102 value is niubility"}

2.2 Use host_vars and group_vars Directories

The default Ansible config directory ( /etc/ansible/ on Linux) can contain host_vars and group_vars sub‑directories for variable files.

Single‑host variables:

| $ cat /etc/ansible/host_vars/10.4.7.101
|---
|user: root
|pass: root@123

Group variables (e.g., for group test):

| $ cat /etc/ansible/group_vars/test
|---
|user: work
|pass: work@123

2.3 Define Variables via var_files

| $ cat vars.yml
|---
|key: jiayou
| $ cat bo.yml
|---
|- hosts: all
|  gather_facts: False
|  vars_files:
|   - vars.yml
|  tasks:
|   - name: display
|     debug: msg="the {{ inventory_hostname }} valus is {{ key }}"
| $ ansible-playbook bo.yml
| PLAY [all]
| TASK [display]
| ok: [10.4.7.101] => {"msg": "the 10.4.7.101 valus is jiayou"}
| ok: [10.4.7.102] => {"msg": "the 10.4.7.102 valus is jiayou"}

2.4 Use vars_prompt for Interactive Input

| $ cat prom.yml
|---
|- hosts: test
|  remote_user: root
|  vars_prompt:
|   - name: "var1"
|     prompt: "please input you name"
|     private: no
|   - name: "var2"
|     prompt: "please input you age"
|     private: yes
|     default: 18
|  tasks:
|   - name: display var1
|     debug: msg="your name of var1 is {{ var1 }}"
|   - name: display var2
|     debug: msg="you age of var2 is {{ var2 }}"
| $ ansible-playbook prom.yml
| please input you name: lvzhenjiang
| please input you age [18]: 23
| TASK [display var1]
| ok: [10.4.7.101] => {"msg": "your name of var1 is lvzhenjiang"}
| TASK [display var2]
| ok: [10.4.7.101] => {"msg": "you age of var2 is 23"}

2.5 Pass Variables on the Command Line ( --extra-vars )

| $ cat exap.yml
|---
|- hosts: '{{hosts}}'
|  remote_user: '{{user}}'
|  tasks:
|   - name: "一个测试"
|     debug: msg="your hosts is {{hosts}}, user is {{user}}"
| $ ansible-playbook exap.yml -e "hosts=test user=root"
| PLAY [test]
| TASK [一个测试]
| ok: [10.4.7.101] => {"msg": "your hosts is test, user is root"}

You can also supply variables from a file using -e "@filename".

| $ cat anhui.yml
|---
|hosts: test
|user: root
| $ ansible-playbook exap.yml -e "@anhui.yml"
| PLAY [test]
| TASK [一个测试]
| ok: [10.4.7.101] => {"msg": "your hosts is test, user is root"}

2.6 Define Variables Inside the Playbook

| $ cat playbook.yml
|---
|- hosts: test
|  remote_user: root
|  vars:
|   - dir1: /root/Ansible
|   - dir2: /root/Ansible/test1
|   - dir3: /root/Ansible/test2
|  tasks:
|   - name: Create New Folder
|     file: name={{ dir1 }} state=directory
|   - name: Create New Folder
|     file: name={{ dir2 }} state=directory
|   - name: Create New Folder
|     file: name={{ dir3 }} state=directory
| $ ansible-playbook playbook.yml
| PLAY [test]
| TASK [Create New Folder]
| changed: [10.4.7.101]

2.7 Define Variables via Roles

| # roles/vars/main.yml
| var1: value1
| var2: value2
| var3: value3
| # tasks/main.yml
| - name: create directory
|   file: name={{ dir }} state=directory
| - name: Get IP Address
|   shell: echo `{{ cmd }}` >> {{ dir }}/{{ file }}
| # vars/main.yml for role
| cmd: hostname -I
| # hosts file example
| [test]
| 10.4.7.101 dir=/root/node2
| 10.4.7.102 dir=/root/node1
| [test:vars]
| file=hostname.txt
| $ ansible-playbook -i hosts playbook.yml
| PLAY [test]
| TASK [test : create directory]
| ok: [10.4.7.101]
| TASK [test : Get IP Address]
| changed: [10.4.7.101]

2.8 Use Facts to Obtain Information

Facts are automatically discovered variables such as the remote host’s IP address or operating system.

| $ ansible test -m setup | grep "ansible_python_version"
| "ansible_python_version": "2.7.5",
| $ ansible test -m setup | grep "ansible_nodename"
| "ansible_nodename": "template",
| $ ansible test -m setup | grep "ansible_hostname"
| "ansible_hostname": "template"

Disable facts to speed up execution:

| $ cat anhui.yml
|---
|- hosts: test
|  gather_facts: no

2.9 Register Variables

The register keyword stores a task’s result in a variable for later use.

| $ cat register.yml
|---
|- hosts: test
|  remote_user: root
|  tasks:
|   - name: register bo_test
|     shell: hostname -I
|     register: info
|   - name: display info
|     debug: msg="this host ip is {{ info['stdout'] }}"
| $ ansible-playbook register.yml
| TASK [display info]
| ok: [10.4.7.101] => {"msg": "this host ip is 10.4.7.101 "}

2.10 hostvars Variable

hostvars

allows you to reference variables of other hosts.

| $ cat test.yml
|---
|- hosts: test
|  remote_user: root
|  gather_facts: False
|  tasks:
|   - name: this is test1
|     debug: msg="She is come from {{ hostvars['10.4.7.101']['addr'] }}"
|   - name: this is test2
|     debug: msg="I am {{ hostvars['10.4.7.102']['user'] }}, and age is {{ hostvars['10.4.7.102']['age'] }}"
| $ ansible-playbook test.yml
| TASK [this is test1]
| ok: [10.4.7.101] => {"msg": "She is come from beijing"}
| TASK [this is test2]
| ok: [10.4.7.101] => {"msg": "I am shibo, and age is 39"}

2.11 List, Loop, and Dictionary Variables

Variables can be lists, which can be iterated with loops.

| $ cat test.yml
|---
|- hosts: test
|  remote_user: root
|  gather_facts: False
|  vars:
|   - list: [1,2,3]
|  tasks:
|   - name: echo
|     debug: msg="{{ list }}"
| $ ansible-playbook test.yml
| TASK [echo]
| ok: [10.4.7.101] => {"msg": [1, 2, 3]}
| $ cat test.yml (loop example)
|---
|- hosts: 10.4.7.101
|  remote_user: root
|  gather_facts: False
|  vars:
|   - list: [1,2,3]
|  tasks:
|   - name: this is loop
|     debug: msg="{{ item }}"
|     with_items: "{{ list }}"
| $ ansible-playbook test.yml
| TASK [this is loop]
| ok: [10.4.7.101] => (item=1) => {"msg": 1}
| ok: [10.4.7.101] => (item=2) => {"msg": 2}
| ok: [10.4.7.101] => (item=3) => {"msg": 3}