List name server from resolv.conf with hostname in one line per host

Question

I need to get the DNS server(s) from my network, I tried using:

- hosts: localhost
  gather_facts: no

  tasks:
    - name: check resolv.conf exists
      stat:
        path: /etc/resolv.conf
      register: resolv_conf
    - name: check nameservers list in resolv.conf
      debug:
        msg: "{{ contents }}"
      vars:
        contents: "{{ lookup('file', '/etc/resolv.conf') | regex_findall('\\s*nameserver\\s*(.*)') }}"
      when: resolv_conf.stat.exists == True

But this does not quite gives the result I need.

Will it be possible to write a playbook in such a way that the result looks like the below?

hostname;dns1;dns2;dnsN

Answer 1

The declaration below gives the list of nameservers

nameservers: "{{ lookup('file', '/etc/resolv.conf').splitlines()|
                 select('match', '^nameserver.*$')|
                 map('split', ' ')|
                 map('last')|list }}"

You can join the hostname and the items on the list

msg: "{{ inventory_hostname }};{{ nameservers|join(';') }}"

---

Notes

1. Example of a complete playbook for testing

- hosts: localhost

  vars:

    nameservers: "{{ lookup('file', '/etc/resolv.conf').splitlines()|
                     select('match', '^nameserver.*$')|
                     map('split', ' ')|
                     map('last')|list }}"

  tasks:
    - debug:
        var: nameservers
    - debug:
        msg: |
          {{ inventory_hostname }};{{ nameservers|join(';') }}

---

2. The simplified declaration below works fine if there is no nameserver.* in the comments

nameservers: "{{ lookup('file', '/etc/resolv.conf')|
                 regex_findall('\\s*nameserver\\s*(.*)') }}"

Unfortunately, the Linux default file /etc/resolv.conf contains the comment:

| # run "systemd-resolve --status" to see details about the actual nameservers.

This regex will match nameservers.

nameservers:
  - s.

You can solve this problem by putting at least one space behind the keyword nameserver.

                 regex_findall('\\s*nameserver\\s+(.*)') }}"

However, this won't help if there is the keyword nameserver in the comment.

---

Q: "No filter named 'split'"

A: There is no filter split in Ansible less than 2.11. Use regex_replace instead

nameservers: "{{ lookup('file', '/etc/resolv.conf').splitlines()|
                 select('match', '^nameserver.*$')|
                 map('regex_replace', '^(.*) (.*)$', '\\2')|list }}"