Ansible SSH private key in source control?

I have been developing an Ansible playbook for a couple of weeks, therefore, my experience with such technology is relatively short. Part of my strategy includes using a custom ansible_ssh_user for provisioning hosts throughout the inventory, however, such user will need its own SSH key pair, which would involve some sort of a plan for holding/storing its correspondent private key. On a production environment, this playbook would be cloned/pulled and run inside a certain playbook node whose role is to provision the rest of the infrastructure.

At first, I was thinking to just put that private key inside the playbook git repository, but I am having second thoughts about it nonetheless, mostly because of somewhat obvious security reasons and common sense around it, hence the reason I need to consult you about this matter.

With this set on the table, here are the follow-up questions:

In an Ansible-based development environment, is it sane/reasonable to hold a private SSH key in source control?
Would this practice be advised only for development environments whereas another local git branch inside the playbook node would be then used to hold the actual production SSH private key?
Would it be better to address this case scenario via Ansible Vault instead?, I have not ever used this before, but regardless of that I cannot yet tell whether this would be a proper case for using it.
In your experience, what would be your approach around this in a production environment?, what would it be considered as the best practice in this particular scenario?

Solution

It's a bad idea to store any kind of plaintext secret in revision control, SSH private keys included. Instead, use ansible-vault to store the private key.

ansible-vault can operate on any file type. Just encrypt the file with

ansible-vault encrypt /path/to/local/private_key

then install the key:

- name: Install a private SSH key
  vars:
    source_key: /path/to/local/private_key
    dest_key: /path/to/remote/private_key
  tasks:
  - name: Ensure .ssh directory exists.
    file: 
      dest: "{{ dest_key | dirname }}"
      mode: 0700 
      owner: user 
      state: directory
  - name: Install ssh key
    copy: 
      src: "{{ source_key }}" 
      dest: "{{ dest_key }}"
      mode: 0600
      owner: user