> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Variable Scoping
> Understanding variable scope in Ansible, including Host Scope, Play Scope, and Global Variables, for effective configuration management and cleaner playbooks.
Understanding variable scope in Ansible is essential for effective configuration management. In this guide, we explore three primary scopes: Host Scope, Play Scope, and Global Variables. Mastering these concepts will help you write cleaner, more modular playbooks and troubleshoot variable-related issues more efficiently.
## Host Scope
Host-specific variables are defined directly in the inventory file or host-specific configurations. These variables are available only when tasks are executed on that host.
Consider the following inventory file where the `dns_server` variable is specified only for host `web2`:
```ini theme={null}
/etc/ansible/hosts
web1 ansible_host=172.20.1.100
web2 ansible_host=172.20.1.101 dns_server=10.5.5.4
web3 ansible_host=172.20.1.102
```
When executing a playbook that prints the `dns_server` variable for all hosts:
```yaml theme={null}
---
- name: Print DNS server
hosts: all
tasks:
- debug:
msg: '{{ dns_server }}'
```
The play output is as follows:
```Ansible theme={null}
PLAY [Check /etc/ansible/hosts file] ***********************************************************************
TASK [debug] ****************************************************************************************
ok: [web1] => {
"dns_server": "VARIABLE IS NOT DEFINED!"
}
ok: [web2] => {
"dns_server": "10.5.5.4"
}
ok: [web3] => {
"dns_server": "VARIABLE IS NOT DEFINED!"
}
```
In this case, the `dns_server` variable is only defined for `web2`, so it is accessible solely in the host scope for that specific host.
## Play Scope
Variables defined within a play are confined to that play's context. They do not persist into subsequent plays unless declared globally. This helps maintain clear boundaries for variable lifecycles within your playbook.
Consider the following playbook that uses the variable `ntp_server` in one play but not in another:
```yaml theme={null}
---
- name: Play1
hosts: web1
vars:
ntp_server: 10.1.1.1
tasks:
- debug:
var: ntp_server
- name: Play2
hosts: web1
tasks:
- debug:
var: ntp_server
```
The output for this playbook is:
```Ansible theme={null}
PLAY [Play1] *********************************************************************
TASK [debug] **********************************************************************
ok: [web1] => {
"ntp_server": "10.1.1.1"
}
PLAY [Play2] *********************************************************************
TASK [debug] **********************************************************************
ok: [web1] => {
"ntp_server": "VARIABLE IS NOT DEFINED!"
}
```
Variables set within a play are only available in that play. In the example above, `ntp_server` is defined in the first play and is not accessible in the second play.
## Global Variables
Global variables are accessible across all plays and tasks within a playbook. A common method to define global variables is by passing them as extra variables using the command line.
Consider a playbook without explicit variable definition in any play:
```yaml theme={null}
---
- name: Play1
hosts: web1
tasks:
- debug:
var: ntp_server
- name: Play2
hosts: web1
tasks:
- debug:
var: ntp_server
```
When you run the playbook with the following command, the `ntp_server` variable is set globally:
```bash theme={null}
$ ansible-playbook playbook.yml --extra-vars "ntp_server=10.1.1.1"
```
The output will show that `ntp_server` is available in both plays:
```Ansible theme={null}
PLAY [Play1] ********************************************************************
TASK [debug] *********************************************************************
ok: [web1] => {
"ntp_server": "10.1.1.1"
}
PLAY [Play2] ********************************************************************
TASK [debug] *********************************************************************
ok: [web1] => {
"ntp_server": "10.1.1.1"
}
```
Passing `ntp_server` as an extra variable sets it as a global variable, making it accessible to every play and task in the playbook.
## Summary of Variable Scopes
| Scope Type | Description | Example Usage |
| ---------------- | ---------------------------------------------------------------------------------------------- | ------------------------------------------------------------------ |
| Host Scope | Variables defined for a specific host are available only when tasks are executed on that host. | Inventory file entries like `dns_server=10.5.5.4` on `web2` |
| Play Scope | Variables set within a play are confined to that play and do not persist to subsequent plays. | Defined with `vars:` in a play block |
| Global Variables | Variables passed via command-line extra-vars or defined globally, accessible across all plays. | `ansible-playbook playbook.yml --extra-vars "ntp_server=10.1.1.1"` |
Having a solid grasp of these scopes will not only help in writing efficient and modular playbooks but also in troubleshooting and managing Ansible configurations effectively.
Thank you for reading this article. Happy automating, and see you in the next guide!