How to set host_key_checking=false in ansible inventory file

Turns out it is possible to enter a host name directly into the playbook, so running the playbook with hosts: imac-2.local will work fine. But it's kind of clunky.

A better solution might be defining the playbook's hosts using a variable, then passing in a specific host address via --extra-vars:

# file: user.yml  (playbook)
---
- hosts: '{{ target }}'
  user: ...

Running the playbook:

ansible-playbook user.yml --extra-vars "target=imac-2.local"

If {{ target }} isn't defined, the playbook does nothing. A group from the hosts file can also be passed through if need be. Overall, this seems like a much safer way to construct a potentially destructive playbook.

Playbook targeting a single host:

$ ansible-playbook user.yml --extra-vars "target=imac-2.local" --list-hosts

playbook: user.yml

  play #1 (imac-2.local): host count=1
    imac-2.local

Playbook with a group of hosts:

$ ansible-playbook user.yml --extra-vars "target=office" --list-hosts

playbook: user.yml

  play #1 (office): host count=3
    imac-1.local
    imac-2.local
    imac-3.local

Forgetting to define hosts is safe!

$ ansible-playbook user.yml --list-hosts

playbook: user.yml

  play #1 ({{target}}): host count=0

Vagrantfile is just a plain ruby file, so you can generate inventory file from it:

File.open('ansible/hosts/vagrant' ,'w') do |f|
  f.write "[default]\n"
  f.write "#{VAGRANT_NETWORK_IP} ansible_ssh_user=vagrant ansible_ssh_private_key_file=~/.vagrant.d/insecure_private_key\n"
end

By default vagrant box starts with name "default", so I usually limit ansible-managed hosts to vagrant's one (you can set ansible.limit = "default").

If you want to have several vagrant boxes with one inventory, you can define that boxes in one Vagrantfile and generate inventory for it.