uclalib_get_ssh_host_keys.yml

---
# Query every host in inventory.ini for ssh host keys, populate
# /etc/ssh/known_hosts
#
# Requires python-netaddr and python-dns to be installed (RHEL7)

- name: uclalib_get_ssh_host_keys.yml
  hosts: all
  user: ansible
  connection: local
  gather_facts: false

  vars:
    working_file: "/tmp/known-hosts"
    output: "/etc/ssh/ssh_known_hosts"
    salt: "{{ 1000000 | random }}"

  tasks:
    - name: Set Working Directory
      set_fact:
        working_directory: "/tmp/ssh-known-hosts-{{ salt }}"
      run_once: true

    - name: Create Working Directory
      file:
        path: "{{ working_directory }}"
        state: directory
      check_mode: false
      run_once: true

    # When the inventory record is an IP, this will cause noise
    - name: Get port from inventory (default 22), look up IP
      set_fact:
        ansible_ssh_port: "{{ hostvars[inventory_hostname]['ansible_ssh_port'] | default('22') }}"
        ansible_inventory_ip: "{{ lookup('dig',inventory_hostname) }}"
        ansible_shortname: "{{ inventory_hostname|regex_replace('\\..*') }}"

    # Relies upon facts set above, must be a separate task
    - name: Assemble query string (hostname vs ip)
      set_fact:
        query_string: |
          "{{ (inventory_hostname | ipaddr)
              | ternary(
                inventory_hostname,
                ansible_inventory_ip + ' ' + inventory_hostname + ',' + ansible_shortname + ',' + ansible_inventory_ip
              )
          }}"

    - name: Ensure ssh host key known
      lineinfile:
        dest: "{{ working_directory }}/{{ inventory_hostname }}"
        create: yes
        state: present
        line: "{{ item }}"
      with_items:
        - "{{ lookup('pipe', 'ssh-keyscan -p' + ansible_ssh_port + ' ' + query_string ).split('\n') }}"
      check_mode: false
      notify: Assemble Host Keys

  handlers:
    - name: Assemble Host Keys
      assemble:
        dest: "{{ working_file }}"
        src: "{{ working_directory }}"
      changed_when: true
      check_mode: false
      run_once: true
      notify: Sort Host Keys

    - name: Sort Host Keys
      command: sort -o {{ working_file }} {{ working_file }}
      environment:
        LC_COLLATE: C
      changed_when: true
      check_mode: false
      run_once: true
      notify: Remove Working Directory

    - name: Remove Working Directory
      file:
        path: "{{ working_directory }}"
        state: absent
      check_mode: false
      run_once: true
      notify:
        - Update {{ output }}
        - Remove Working File

    - name: Update {{ output }}
      copy:
        dest: '{{ output }}'
        src: '{{ working_file }}'
      become: true
      run_once: true

    - name: Remove Working File
      file:
        path: "{{ working_file }}"
        state: absent
      run_once: true