Ansible: Iterate over variables and run command if variable is defined

Question

I want to set nameservers in /etc/resolv.conf using ansible. I basically want to set variables (DNS1, DNS2, DNS3). I only want to apply DNS# if it is defined. I have the following so far.

# Run this playbook on all hosts that should query the DNS server.
- hosts: all
  vars:
    # dns_server: 192.168.1.190
    nameserver_ip: 192.168.1.214
    DNS2: 192.168.1.1
  tasks:
    - name: Add DNS server's IPv4 address to /etc/resolv.conf
      command: "nmcli con mod {{ ansible_default_ipv4['interface'] }} ipv4.dns {{ nameserver_ip }}"
    - name: Add non-authoritative DNS servers to /etc/resolv.conf
      shell: "nmcli con mod {{ ansible_default_ipv4['interface'] }} +ipv4.dns {{ item }}"
      when:  item is defined
      with_items:
        - DNS2
        - DNS3
    - name: Restart default network interface to update /etc/resolv.conf
      shell: "nmcli con reload && nmcli con up {{ ansible_default_ipv4['interface'] }}"

However, when I run this I get the following error

[root@ns1 dns]# ansible-playbook --user root -i ftp.home, dns_client.yaml -k
...
...
TASK [Add non-authoritative DNS servers to /etc/resolv.conf] *****************************************************************************************************************************************************
failed: [ftp.home] (item=DNS2) => {"changed": true, "cmd": "nmcli con mod eth0 +ipv4.dns DNS2", "delta": "0:00:00.055982", "end": "2019-04-01 12:25:53.029983", "item": "DNS2", "msg": "non-zero return code", "rc": 2, "start": "2019-04-01 12:25:52.974001", "stderr": "Error: failed to modify ipv4.dns: invalid IPv4 address 'DNS2'.", "stderr_lines": ["Error: failed to modify ipv4.dns: invalid IPv4 address 'DNS2'."], "stdout": "", "stdout_lines": []}
failed: [ftp.home] (item=DNS3) => {"changed": true, "cmd": "nmcli con mod eth0 +ipv4.dns DNS3", "delta": "0:00:00.056684", "end": "2019-04-01 12:25:53.782999", "item": "DNS3", "msg": "non-zero return code", "rc": 2, "start": "2019-04-01 12:25:53.726315", "stderr": "Error: failed to modify ipv4.dns: invalid IPv4 address 'DNS3'.", "stderr_lines": ["Error: failed to modify ipv4.dns: invalid IPv4 address 'DNS3'."], "stdout": "", "stdout_lines": []}
        to retry, use: --limit @/root/ansible/dns/dns_client.retry

It seems that, instead of using the value of DNS{2,3} it is just using the variable names (literally) DNS2 and DNS3. What am I doing wrong here?

Answer 1

I figured it out. I forgot that in order to used the value of a variable in Ansible you must surround the variable name in "{{ ... }}". The following changes fixed my issue.

  with_items:
    - "{{ DNS2 }}"
    - "{{ DNS3 }}"