Ansible terminology - ansible_hostname vs inventory_hostname vs ansible

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

March 11, 2022

#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=sshansible_user=devopsansible_ssh_private_key_file=~/.ssh/id_rsa

execution

ansible-pilot $ ansible-playbook -i ansible\ statements/inventory ansible\ statements/hostnames.ymlPLAY [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=0ansible-pilot $

idempotency

ansible-pilot $ ansible-playbook -i ansible\ statements/inventory ansible\ statements/hostnames.ymlPLAY [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=0ansible-pilot $

before execution

ansible-pilot $ ssh [emailprotected][devops@demo ~]$ uname -aLinux 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 -ndemo.example.com[devops@demo ~]$ hostnamedemo.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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Ansible terminology - ansible_hostname vs inventory_hostname vs ansible_fqdn (2024)