Ansible terminology - ansible_hostname vs inventory_hostname vs ansible_fqdn

What is the difference between ansible_hostname vs inventory_hostname vs ansible_fqdn in a practical example with Ansible Playbook?

March 11, 2022

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#ansible #terminology #ansible_hostname #inventory_hostname #ansible_fqdn #variables #ansible-internal #tricks

What is the difference between ansible_hostname vs inventory_hostname?

These two ansible internal variables sometimes confuse one for another but they’re fundamentally different. I’m Luca Berton and welcome to today’s episode of Ansible Pilot.

ansible_hostname vs inventory_hostname vs ansible_fqdn

ansible_hostname and ansible_fqdn

Read from the target machine hostname from the facts:

ansible_hostname read the hostname from the facts collected during the gather_facts
Same as the uname -n or hostname command-line
Need gather_facts enabled, otherwise the ansible_facts variable would be unavailable to use in your playbook
Same as hostname of the target host
As this is based on the gather_facts step. ansible_hostname not available in ad-hoc command

inventory_hostname

Read from Ansible inventory or hosts files:

inventory_hostname read the hostname from the inventory configuration or the hosts file. Could be different from the hostname configuration of the remote system. It could be only a name on the controller machine
inventory_hostname is always available to use in your playbook.
Could be different from the hostname of the target host
Available for both playbook and ad-hoc command

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demo

Let me show you the difference between ansible_hostname vs inventory_hostname vs ansible_fqdn internal variables in a simple Ansible Playbook.

code

hostnames.yml

---
- name: hostnames demo
  hosts: all
  gather_facts: true
  tasks:
    - name: print inventory_hostname
      ansible.builtin.debug:
        var: inventory_hostname
    - name: print ansible_hostname
      ansible.builtin.debug:
        var: ansible_hostname
    - name: print ansible_fqdn
      ansible.builtin.debug:
        var: ansible_fqdn

inventory

foo.example.com ansible_host=192.168.0.190
[all:vars]
ansible_connection=ssh
ansible_user=devops
ansible_ssh_private_key_file=~/.ssh/id_rsa

execution

ansible-pilot $ ansible-playbook -i ansible\ statements/inventory ansible\ statements/hostnames.yml
PLAY [hostnames demo] *****************************************************************************
TASK [Gathering Facts] ****************************************************************************
ok: [foo.example.com]
TASK [print inventory_hostname] *******************************************************************
ok: [foo.example.com] => {
    "inventory_hostname": "foo.example.com"
}
TASK [print ansible_hostname] *********************************************************************
ok: [foo.example.com] => {
    "ansible_hostname": "demo"
}
TASK [print ansible_fqdn] *************************************************************************
ok: [foo.example.com] => {
    "ansible_fqdn": "demo.example.com"
}
PLAY RECAP ****************************************************************************************
foo.example.com            : ok=4    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0
ansible-pilot $

idempotency

ansible-pilot $ ansible-playbook -i ansible\ statements/inventory ansible\ statements/hostnames.yml
PLAY [hostnames demo] *****************************************************************************
TASK [Gathering Facts] ****************************************************************************
ok: [foo.example.com]
TASK [print inventory_hostname] *******************************************************************
ok: [foo.example.com] => {
    "inventory_hostname": "foo.example.com"
}
TASK [print ansible_hostname] *********************************************************************
ok: [foo.example.com] => {
    "ansible_hostname": "demo"
}
TASK [print ansible_fqdn] *************************************************************************
ok: [foo.example.com] => {
    "ansible_fqdn": "demo.example.com"
}
PLAY RECAP ****************************************************************************************
foo.example.com            : ok=4    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0
ansible-pilot $

before execution

ansible-pilot $ ssh [email protected]
[devops@demo ~]$ uname -a
Linux demo.example.com 4.18.0-348.el8.x86_64 #1 SMP Mon Oct 4 12:17:22 EDT 2021 x86_64 x86_64 x86_64 GNU/Linux
[devops@demo ~]$ uname -n
demo.example.com
[devops@demo ~]$ hostname
demo.example.com
[devops@demo ~]$

Recap

Now you know more about the Ansible internal variables ansible_hostname, inventory_hostname and ansible_fqdn. You know how to use it based on your use case.

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