Mastering Ansible Inventory: From Basics to Advanced Grouping & Variables

What is Ansible Inventory?

Ansible Inventory is a file or database that stores a list of hosts and related configuration information, allowing you to specify target machines and set variables such as IP addresses, usernames, and passwords to simplify task execution.

Basic Inventory File

<code>$ cat hosts
172.139.20.170

[k8sMaster]
172.139.20.121
172.139.20.176
172.139.20.151

[k8sNode]
172.139.20.175
172.139.20.75
172.139.20.66
172.139.20.19

# Support host range syntax
[tmp]
172.139.20.[1:20]
www[01:50].example.com
db-[a:f].example.com</code>

Tip: Group names should not contain hyphens; otherwise Ansible will emit a warning about invalid characters.

Validate Inventory File

Using the ping module:

<code>$ ansible -i hosts k8sMaster -m ping --ssh-common-args="-o StrictHostKeyChecking=no" -u ops -k
SSH password: 
172.139.20.176 | SUCCESS => {"ansible_facts": {"discovered_interpreter_python": "/usr/bin/python"}, "changed": false, "ping": "pong"}
172.139.20.151 | SUCCESS => {"ansible_facts": {"discovered_interpreter_python": "/usr/bin/python"}, "changed": false, "ping": "pong"}
172.139.20.121 | SUCCESS => {"ansible_facts": {"discovered_interpreter_python": "/usr/bin/python"}, "changed": false, "ping": "pong"}</code>

Parameters explained:

-i hosts k8sMaster: Use the inventory file and specify the target group or host.

-m ping: Run the ping module to test connectivity.

--ssh-common-args="-o StrictHostKeyChecking=no": Disable SSH host key checking.

-u ops: Remote user for login.

-k: Prompt for the SSH password.

Using the file module (without privilege escalation):

<code>$ ansible -i hosts 172.139.20.121 --ssh-common-args="-o StrictHostKeyChecking=no" -u ops -k -m file -a "path=/etc/foo.conf state=touch"
SSH password: 
172.139.20.121 | FAILED! => {"ansible_facts": {"discovered_interpreter_python": "/usr/bin/python"}, "changed": false, "msg": "Error, could not touch target: [Errno 13] Permission denied: '/etc/foo.conf'", "path": "/etc/foo.conf"}</code>

Tip: The failure is due to insufficient permissions for the

ops

user. Use privilege escalation to succeed.

Privilege escalation parameters:

-b: Enable become (privilege escalation).

--become-method: Method to become, e.g., sudo or su (default sudo).

-K: Prompt for the become password.

<code>$ ansible -i hosts 172.139.20.121 --ssh-common-args="-o StrictHostKeyChecking=no" -u ops -k -m file -a "path=/etc/foo.conf state=touch" -b -K
SSH password: 
BECOME password[defaults to SSH password]: 
172.139.20.121 | CHANGED => {"ansible_facts": {"discovered_interpreter_python": "/usr/bin/python"}, "changed": true, "dest": "/etc/foo.conf", "gid": 0, "group": "root", "mode": "0644", "owner": "root", "size": 0, "state": "file", "uid": 0}</code>

Advanced Usage: Grouping and Variable Settings

When environments become more complex, simple host lists are insufficient. Use inventory grouping and variables to organize hosts.

Defining groups:

<code>[group1]
192.168.xx.xx
10.154.15.45

[group2]
192.167.xx.xx</code>

Defining sub‑groups:

<code>[k8sMaster]
10.154.15.[45:47]

[k8sNode]
10.154.15.56
10.154.15.89
10.154.15.[100:109]

[k8s:children]
k8sMaster
k8sNode</code>

Variables reduce repetitive parameters. Common variables include:

ansible_port: SSH port of the target host.

ansible_user: Remote login user.

ansible_password: Remote login password.

ansible_become: Enable privilege escalation.

ansible_become_method: Method for escalation (sudo or su).

ansible_become_user: User for

su

escalation.

ansible_become_password: Password for escalation.

ansible_python_interpreter: Path to Python on the target.

Example using sudo escalation:

<code>172.139.20.170 ansible_port=22 ansible_user=ops ansible_password=ops_password ansible_become=yes ansible_become_method=sudo ansible_become_password=ops_password</code>

Example using su escalation:

<code>172.139.20.170 ansible_port=22 ansible_user=ops ansible_password=ops_password ansible_become=yes ansible_become_method=su ansible_become_user=root ansible_become_password=root_password</code>

Setting variables for an entire group:

<code>[k8sMaster]
172.139.20.121
172.139.20.176
172.139.20.151

[k8sNode]
172.139.20.175
172.139.20.75
172.139.20.66
172.139.20.19

[k8s:children]
k8sMaster
k8sNode

[k8s:vars]
ansible_user=ops
ansible_password=ops.ecloud.com</code>

Reference Articles

Official Ansible documentation: https://docs.ansible.com/ansible/2.9/user_guide/intro_inventory.html#

Related blog post: https://www.cnblogs.com/jiaxzeng/p/17506341.html

Conclusion

The above only scratches the surface of Ansible Inventory usage. As you deepen your understanding and practice, the inventory file becomes a powerful tool for automated deployment, configuration management, and task orchestration, helping you boost efficiency and reliability.