Ansible copy ssh key from one host to another

This does the trick for me, it collects the public ssh keys on the nodes and distributes it over all the nodes. This way they can communicate with each other.

- hosts: controllers
  gather_facts: false
  remote_user: root
  tasks:
    - name: fetch all public ssh keys
      shell: cat ~/.ssh/id_rsa.pub
      register: ssh_keys
      tags:
        - ssh

    - name: check keys
      debug: msg="{{ ssh_keys.stdout }}"
      tags:
        - ssh

    - name: deploy keys on all servers
      authorized_key: user=root key="{{ item[0] }}"
      delegate_to: "{{ item[1] }}"
      with_nested:
        - "{{ ssh_keys.stdout }}"
        - "{{groups['controllers']}}"
      tags:
        - ssh

Info: This is for the user root

I created a parameterized role to make sure ssh key pair is generated in a source user in a source remote host and its public key copied to a target user in a target remote host.

You can invoke that role in a nested loop of source and target host lists as shown at the bottom:

---
#****h* ansible/ansible_roles_ssh_authorize_user
# NAME
#   ansible_roles_ssh_authorize_user - Authorizes user via ssh keys
#
# FUNCTION
#
#   Copies user's SSH public key from a source user in a source host
#   to a target user in a target host
#
# INPUTS
#
#   * ssh_authorize_user_source_user
#   * ssh_authorize_user_source_host
#   * ssh_authorize_user_target_user
#   * ssh_authorize_user_target_host
#****
#****h* ansible_roles_ssh_authorize_user/main.yml
# NAME
#   main.yml - Main playbook for role ssh_authorize_user
# HISTORY
#   $Id: $
#****

- assert:
    that:
      - ssh_authorize_user_source_user != ''
      - ssh_authorize_user_source_host != ''
      - ssh_authorize_user_target_user != ''
      - ssh_authorize_user_target_host != ''
  tags:
    - check_vars
- name: Generate SSH Keypair in Source
  user:
    name: "{{ ssh_authorize_user_source_user }}"
    state: present
    ssh_key_comment: "ansible-generated for {{ ssh_authorize_user_source_user }}@{{ ssh_authorize_user_source_host }}"
    generate_ssh_key: yes
  delegate_to: "{{ ssh_authorize_user_source_host }}"
  register: source_user
- name: Install SSH Public Key in Target
  authorized_key:
    user: "{{ ssh_authorize_user_target_user }}"
    key: "{{ source_user.ssh_public_key }}"
  delegate_to: "{{ ssh_authorize_user_target_host }}"
- debug:
    msg: "{{ ssh_authorize_user_source_user }}@{{ ssh_authorize_user_source_host }} authorized to log in to {{ ssh_authorize_user_target_user }}@{{ ssh_authorize_user_target_host }}"

Invoking role in a loop:

- name: Authorize User
  include_role:
    name: ssh_authorize_user
  vars:
    ssh_authorize_user_source_user: "{{ git_user }}"
    ssh_authorize_user_source_host: "{{ item[0] }}"
    ssh_authorize_user_target_user: "{{ git_user }}"
    ssh_authorize_user_target_host: "{{ item[1] }}"
  with_nested:
    - "{{ app_server_list }}"
    - "{{ git_server_list }}"

Take a look to the authorized_key module for getting info on how to manage your public keys.

The most straightforward solution I can think of would be to generate a fresh key pair for your application, to be shared accross all your app instances. This may have security implications (you are indeed sharing keys between all instances!), but it'll simplify a lot the provisioning process.

You'll also require a deploy user on each app machine, to be used later on during deployment process. You'll need your public key (or jenkins one) on each deploy user's authorized_keys.

A sketch playbook:

---
- name: ensure app/deploy public key is present on git server
  hosts: gitserver
  tasks:
    - name: ensure app public key
      authorized_key: 
        user: "{{ git_user }}" 
        key: app_keys/id_dsa.pub 
        state: present

- name: provision app servers
  hosts: appservers
  tasks:
    - name: ensure app/deploy user is present
      user: 
        name: "{{ deploy_user }}"
        state: present

    - name: ensure you'll be able to deploy later on
      authorized_key:
        user: "{{ deploy_user }}" 
        key: "{{ path_to_your_public_key }}" 
        state: present

    - name: ensure private key and public one are present
      copy: 
        src: keys/myapp.private 
        dest: "/home/{{ deploy_user }}/.ssh/{{ item }}" 
        mode: 0600
      with_items:
        - app_keys/id_dsa.pub
        - app_keys/id_dsa