How to set host_key_checking=false in ansible inventory file?

Question

^{Due to the fact that I answered this in 2014, I have updated my answer to account for more recent versions of ansible.}

Yes, you can do it at the host/inventory level (Which became possible on newer ansible versions) or global level:

inventory:

Add the following.

ansible_ssh_common_args='-o StrictHostKeyChecking=no'

host:

Add the following.

ansible_ssh_extra_args='-o StrictHostKeyChecking=no'

hosts/inventory options will work with connection type ssh and not paramiko. Some people may strongly argue that inventory and hosts is more secure because the scope is more limited.

global:

Ansible User Guide - Host Key Checking

• You can do it either in the /etc/ansible/ansible.cfg or ~/.ansible.cfg file:

  [defaults]
  host_key_checking = False
  

• Or you can setup and env variable (this might not work on newer ansible versions):

  export ANSIBLE_HOST_KEY_CHECKING=False
  

Yes, you can set this on the inventory/host level.

^{With an already accepted answer present, I think this is a better answer to the question on how to handle this on the inventory level. I consider this more secure by isolating this insecure setting to the hosts required for this (e.g. test systems, local development machines).}

What you can do at the inventory level is add

ansible_ssh_common_args='-o StrictHostKeyChecking=no'

or

ansible_ssh_extra_args='-o StrictHostKeyChecking=no'

to your host definition (see Ansible Behavioral Inventory Parameters).

This will work provided you use the ssh connection type, not paramiko or something else).

For example, a Vagrant host definition would look like…

vagrant ansible_port=2222 ansible_host=127.0.0.1 ansible_ssh_common_args='-o StrictHostKeyChecking=no'

or

vagrant ansible_port=2222 ansible_host=127.0.0.1 ansible_ssh_extra_args='-o StrictHostKeyChecking=no'

Running Ansible will then be successful without changing any environment variable.

$ ansible vagrant -i <path/to/hosts/file> -m ping
vagrant | SUCCESS => {
    "changed": false, 
    "ping": "pong"
}

In case you want to do this for a group of hosts, here's a suggestion to make it a supplemental group var for an existing group like this:

[mytestsystems]
test[01:99].example.tld

[insecuressh:children]
mytestsystems

[insecuressh:vars]
ansible_ssh_common_args='-o StrictHostKeyChecking=no'

I could not use:

ansible_ssh_common_args='-o StrictHostKeyChecking=no'

in inventory file. It seems ansible does not consider this option in my case (ansible 2.0.1.0 from pip in ubuntu 14.04)

I decided to use:

server ansible_host=192.168.1.1 ansible_ssh_common_args= '-o UserKnownHostsFile=/dev/null'

It helped me.

Also you could set this variable in group instead for each host:

[servers_group:vars]
ansible_ssh_common_args='-o UserKnownHostsFile=/dev/null'

In /etc/ansible/ansible.cfg uncomment the line:

host_key_check = False

and in /etc/ansible/hosts uncomment the line

client_ansible ansible_ssh_host=10.1.1.1 ansible_ssh_user=root ansible_ssh_pass=12345678

That's all