How to ignore ansible SSH authenticity checking?

Question

Is there a way to ignore the SSH authenticity checking made by Ansible? For example when I've just setup a new server I have to answer yes to this question:

GATHERING FACTS ***************************************************************
The authenticity of host 'xxx.xxx.xxx.xxx (xxx.xxx.xxx.xxx)' can't be established.
RSA key fingerprint is xx:yy:zz:....
Are you sure you want to continue connecting (yes/no)?

I know that this is generally a bad idea but I'm incorporating this in a script that first creates a new virtual server at my cloud provider and then automatically calls my ansible playbook to configure it. I want to avoid any human intervention in the middle of the script execution.

Answer 1

Two options - the first, as you said in your own answer, is setting the environment variable ANSIBLE_HOST_KEY_CHECKING to False.

The second way to set it is to put it in an ansible.cfg file, and that's a really useful option because you can either set that globally (at system or user level, in /etc/ansible/ansible.cfg or ~/.ansible.cfg), or in an config file in the same directory as the playbook you are running.

To do that, make an ansible.cfg file in one of those locations, and include this:

[defaults]
host_key_checking = False

You can also set a lot of other handy defaults there, like whether or not to gather facts at the start of a play, whether to merge hashes declared in multiple places or replace one with another, and so on. There's a whole big list of options here in the Ansible docs.

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Edit: a note on security.

SSH host key validation is a meaningful security layer for persistent hosts - if you are connecting to the same machine many times, it's valuable to accept the host key locally.

For longer-lived EC2 instances, it would make sense to accept the host key with a task run only once on initial creation of the instance:

  - name: Write the new ec2 instance host key to known hosts
    connection: local
    shell: "ssh-keyscan -H {{ inventory_hostname }} >> ~/.ssh/known_hosts"

There's no security value for checking host keys on instances that you stand up dynamically and remove right after playbook execution, but there is security value in checking host keys for persistent machines. So you should manage host key checking differently per logical environment.

• Leave checking enabled by default (in ~/.ansible.cfg)
• Disable host key checking in the working directory for playbooks you run against ephemeral instances (./ansible.cfg alongside the playbook for unit tests against vagrant VMs, automation for short-lived ec2 instances)