Override hosts variable of Ansible playbook from the command line

Question

This is a fragment of a playbook that I\'m using (server.yml):

- name: Determine Remote User
  hosts: web
  gather_facts: false
  roles:
    - {         


        

Answer 1

This is a bit late, but I think you could use the --limit or -l command to limit the pattern to more specific hosts. (version 2.3.2.0)

You could have - hosts: all (or group) tasks: - some_task

and then ansible-playbook playbook.yml -l some_more_strict_host_or_pattern and use the --list-hosts flag to see on which hosts this configuration would be applied.

Answer 2

Here's a cool solution I came up to safely specify hosts via the --limit option. In this example, the play will end if the playbook was executed without any hosts specified via the --limit option.

This was tested on Ansible version 2.7.10

---
- name: Playbook will fail if hosts not specified via --limit option.
  # Hosts must be set via limit. 
  hosts: "{{ play_hosts }}"
  connection: local
  gather_facts: false
  tasks:
  - set_fact:
      inventory_hosts: []
  - set_fact:
      inventory_hosts: "{{inventory_hosts + [item]}}"
    with_items: "{{hostvars.keys()|list}}"

  - meta: end_play
    when: "(play_hosts|length) == (inventory_hosts|length)"

  - debug:
      msg: "About to execute tasks/roles for {{inventory_hostname}}"

Answer 3

I am using ansible 2.5 (2.5.3 exactly), and it seems that the vars file is loaded before the hosts param is executed. So you can set the host in a vars.yml file and just write hosts: {{ host_var }} in your playbook

For example, in my playbook.yml:

---
- hosts: "{{ host_name }}"
  become: yes
  vars_files:
    - vars/project.yml
  tasks:
    ... 

And inside vars/project.yml:

---

# general
host_name: your-fancy-host-name

Answer 4

For anyone who might come looking for the solution.
Play Book

- hosts: '{{ host }}'
  tasks:
  - debug: msg="Host is {{ ansible_fqdn }}"

Inventory

[web]
x.x.x.x

[droplets]
x.x.x.x

Command: ansible-playbook deplyment.yml -i hosts --extra-vars "host=droplets" So you can specify the group name in the extra-vars

Answer 5

I changed mine to default to no host and have a check to catch it. That way the user or cron is forced to provide a single host or group etc. I like the logic from the comment from @wallydrag. The empty_group contains no hosts in the inventory.

- hosts: "{{ variable_host | default('empty_group') }}"

Then add the check in tasks:

   tasks:
   - name: Fail script if required variable_host parameter is missing
     fail:
       msg: "You have to add the --extra-vars='variable_host='"
     when: (variable_host is not defined) or (variable_host == "")

Answer 6

An other solution is to use the special variable ansible_limit which is the contents of the --limit CLI option for the current execution of Ansible.

- hosts: "{{ ansible_limit | default(omit) }}"

If the --limit option is omitted, then Ansible issues a warning, but does nothing since no host matched.

[WARNING]: Could not match supplied host pattern, ignoring: None

PLAY ****************************************************************
skipping: no hosts matched