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

I don't think Ansible provides this feature, which it should. Here's something that you can do:

hosts: "{{ variable_host | default('web') }}"

and you can pass variable_host from either command-line or from a vars file, e.g.:

ansible-playbook server.yml --extra-vars "variable_host=newtarget(s)"

Answer 2

We use a simple fail task to force the user to specify the Ansible limit option, so that we don't execute on all hosts by default/accident.

The easiest way I found is this:

---
- name: Force limit
  # 'all' is okay here, because the fail task will force the user to specify a limit on the command line, using -l or --limit
  hosts: 'all'

  tasks:
  - name: checking limit arg
    fail:
      msg: "you must use -l or --limit - when you really want to use all hosts, use -l 'all'"
    when: ansible_limit is not defined
    run_once: true

Now we must use the -l (= --limit option) when we run the playbook, e.g.

ansible-playbook playbook.yml -l www.example.com

Limit option docs:

Limit to one or more hosts This is required when one wants to run a playbook against a host group, but only against one or more members of that group.

Limit to one host

ansible-playbook playbooks/PLAYBOOK_NAME.yml --limit "host1"

Limit to multiple hosts

ansible-playbook playbooks/PLAYBOOK_NAME.yml --limit "host1,host2"

Negated limit.
NOTE: Single quotes MUST be used to prevent bash interpolation.

ansible-playbook playbooks/PLAYBOOK_NAME.yml --limit 'all:!host1'

Limit to host group

ansible-playbook playbooks/PLAYBOOK_NAME.yml --limit 'group1'

Answer 3

If you want to run a task that's associated with a host, but on different host, you should try delegate_to.

In your case, you should delegate to your localhost (ansible master) and calling ansible-playbook command

Answer 4

Just came across this googling for a solution. Actually, there is one in Ansible 2.5. You can specify your inventory file with --inventory, like this: ansible --inventory configs/hosts --list-hosts all

Answer 5

I'm using another approach that doesn't need any inventory and works with this simple command:

ansible-playbook site.yml -e working_host=myhost

To perform that, you need a playbook with two plays:

• first play runs on localhost and add a host (from given variable) in a known group in inmemory inventory
• second play runs on this known group

A working example (copy it and runs it with previous command):

- hosts: localhost
  connection: local
  tasks:
  - add_host:
      name: "{{ working_host }}"
      groups: working_group
    changed_when: false

- hosts: working_group
  gather_facts: false
  tasks:
  - debug:
      msg: "I'm on {{ ansible_host }}"

I'm using ansible 2.4.3 and 2.3.3