Local Action

In some situations you can execute a task on a local host, the host where Ansible is running.

Imagine you need to find an IP address of a hostname. This task does not need to be executed on a remote host, as the information is available on the any host, including the Ansible controller, where Ansible is running.

You can either use the delegate_to parameter or the local_action module. The next example does the exact same thing, so pick the one you like the most.

Local action

- name: Configure /etc/hosts
  hosts: all

  tasks:
    - name: Find IP address of a hostname
      local_action:
        module: ansible.builtin.command
        cmd: "dig +short "
      register: ip_address
    
    - name: Write the IP address to /etc/hosts
      ansible.builtin.lineinfile:
        path: /etc/hosts
        create: yes
        line: " "

Delegate to

- name: Configure /etc/hosts
  hosts: all

  tasks:
    - name: Find IP address of a hostname
      ansible.builtin.command: "dig +short "
      register: ip_address
      delegate_to: localhost
    
    - name: Write the IP address to /etc/hosts
      ansible.builtin.lineinfile:
        path: /etc/hosts
        create: yes
        line: " "
        regexp: "^ "

NOTE: The command dig needs to be available on the host where Ansible is running. You could write a task for it.

Situations where this may be useful:

• You need to (un-)register a host from some kind of tool.
• You want to keep track of the last time a playbook was executed.
• You want to send a message to a chat tool.

Assignment

Write a small playbook that writes the date as found on a machine, on the host where Ansible is running using either local_action or delegate_to.

Note 1: The date is stored in a variable called ansible_date_time. Note 2: Use serial: 1 in order to write results machine-by-machine, preventing overwrites.

Solution

See this playbook setup.