Creating an Ansible DNS playbook is a practical way to automate DNS client configuration across multiple Linux servers. Maintaining consistent DNS settings helps ensure reliable network communication and simplifies administration in environments with many managed hosts.
On Red Hat Enterprise Linux systems, NetworkManager is responsible for managing network connections and can dynamically update DNS settings in the /etc/resolv.conf file. By using Ansible, administrators can define the desired DNS configuration and apply it consistently across all managed nodes.
In this guide, we will create an Ansible playbook to configure DNS settings through NetworkManager. You will learn how to build the inventory, define the playbook tasks, apply DNS changes, and validate the final configuration on managed servers.
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By default, NetworkManager dynamically updates the /etc/resolv.conf file with the DNS settings from the active NetworkManager connection profiles
What is NetworkManager?
In some Linux distributions, the default networking service is provided by NetworkManager, which is a dynamic network control and configuration daemon to keep network devices and connections up and active when they are available. The traditional ifcfg type configuration files are still supported.
NetworkManager is installed by default on Red Hat Enterprise Linux. So, in our case, since we’re using a Linux distribution that has it by default, we’ll not install anything to use NetworkManager.
So, let’s get started and create an Ansible playbook to keep the DNS configuration consistent on all hosts.
Creating the Inventory
Before going forward, our environment is composed of:
- One Control VM (A CentOS 9 VM that runs Ansible).
- Six Managed VMs (Red Hat 8 VMs that Ansible manages).
So, Ansible needs to know which hosts to handle. Let’s create a directory to store the inventory file:
mkdir -p /root/ansible/inventoryCreate the hosts.ini file:
touch /root/ansible/inventory/hosts.iniAnd then, add the hosts to hosts.ini. In this case, for instance, our inventory file has some groups
[hpc2_login_nodes] # This is a group
hpc2-login
[hpc2_head_nodes] # This is a group
hpc2-head
[hpc2_compute_nodes] # This is a group
hpc2-node[01:06]
[all:vars] # This is a variable section
ansible_user=root # This is a variable applies to all hostsCreating the Playbook
Let’s create a directory to store the playbook files:
mkdir -p /root/ansible/playbooksInside the playbooks directory, generate the playbook file dns.yml:
touch /root/ansible/playbooks/dns.ymlAnd then, add the following content:
---
- name: Ensure DNS settings using NetworkManager
hosts: all
become: yes
tasks:
- name: Set DNS on interface
community.general.nmcli:
conn_name: "ens192"
type: ethernet
dns4:
- "192.168.255.3"
dns4_search:
- "lab.local"
state: present
notify: Reactivate connection to apply DNS changes
handlers:
- name: Reactivate connection to apply DNS changes
command: nmcli connection up ens192Notes:
- In our case, for instance, all managed nodes have an interface “ens192”.
- Our DNS server IP is “192.168.255.3”.
- Our DNS domain name is “lab.local”.
Running the Playbook
To run the playbook:
ansilble-playbook -i inventory/hosts.ini playbooks/dns.ymlOutput’s example – Considering that all managed hosts are in the desired state (no change):
PLAY [Ensure DNS settings using NetworkManager] *****************************************************************************************************************************
TASK [Gathering Facts] ******************************************************************************************************************************************************
ok: [hpc2-login]
ok: [hpc2-node03]
ok: [hpc2-node01]
ok: [hpc2-node02]
ok: [hpc2-head]
ok: [hpc2-node04]
ok: [hpc2-node05]
ok: [hpc2-node06]
TASK [Set DNS on interface] *************************************************************************************************************************************************
ok: [hpc2-head]
ok: [hpc2-login]
ok: [hpc2-node01]
ok: [hpc2-node02]
ok: [hpc2-node03]
ok: [hpc2-node04]
ok: [hpc2-node05]
ok: [hpc2-node06]
PLAY RECAP ******************************************************************************************************************************************************************
hpc2-head :ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-login :ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-node01 :ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-node02 :ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-node03 :ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-node04 :ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-node05 :ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-node06 : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0If we access one managed node and inspect the DNS configuration, we can confirm that it is correct:
[root@hpc2-node01 ~]# cat /etc/resolv.conf
# Generated by NetworkManager
search lab.local
nameserver 192.168.255.3Supposing that you have a demand to change the DNS IP from 192.168.255.3 to 10.10.10.10 on all managed hosts, you just need to change the IP in the Playbook and rerun it:
PLAY [Ensure DNS settings using NetworkManager] *****************************************************************************************************************************
TASK [Gathering Facts] ******************************************************************************************************************************************************
ok: [hpc2-node02]
ok: [hpc2-login]
ok: [hpc2-node01]
ok: [hpc2-node03]
ok: [hpc2-head]
ok: [hpc2-node04]
ok: [hpc2-node06]
ok: [hpc2-node05]
TASK [Set DNS on interface] *************************************************************************************************************************************************
changed: [hpc2-node02]
changed: [hpc2-node01]
changed: [hpc2-node03]
changed: [hpc2-login]
changed: [hpc2-head]
changed: [hpc2-node04]
changed: [hpc2-node05]
changed: [hpc2-node06]
RUNNING HANDLER [Reactivate connection to apply DNS changes] ****************************************************************************************************************
changed: [hpc2-login]
changed: [hpc2-node01]
changed: [hpc2-head]
changed: [hpc2-node02]
changed: [hpc2-node03]
changed: [hpc2-node04]
changed: [hpc2-node05]
changed: [hpc2-node06]
PLAY RECAP ******************************************************************************************************************************************************************
hpc2-head :ok=3changed=2 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-login :ok=3changed=2 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-node01 :ok=3changed=2 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-node02 :ok=3changed=2 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-node03 :ok=3changed=2 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-node04 :ok=3changed=2 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-node05 :ok=3changed=2 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
hpc2-node06 :ok=3changed=2 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0And inspecting the managed host again, we can confirm the change:
[root@hpc2-node01 ~]# cat /etc/resolv.conf
# Generated by NetworkManager
search lab.local
nameserver 10.10.10.10That’s it for now 🙂
