Using Ansible Playbook to Set Hostnames and Update /etc/hosts on Multiple Servers

Playbook Introduction

An Ansible Playbook is a more powerful and flexible alternative to using the Ansible command line directly. It is a simple configuration‑management and multi‑host deployment system described in YAML, allowing ordered execution of tasks synchronously or asynchronously.

1. Hostnames of the two servers

Server 192.168.20.40:

[root@docker02 ~]# hostname

docker02

Server 192.168.20.39:

[root@slavedb tmp]# hostname

slavedb

2. Ansible configuration

# /etc/ansible/hosts

[web]

k8s-master ansible_ssh_host=192.168.20.40

k8s-node3  ansible_ssh_host=192.168.20.39

3. Playbook configuration (host.yml)

---

- hosts: web

tasks:

- name: hostname

shell: hostnamectl set-hostname {{ inventory_hostname }}

when: ansible_distribution_major_version == "7"

4. Execute the playbook

[root@docker02 ~]# ansible-playbook host.yml

Verify hostnames after execution:

[root@docker02 ~]# hostname

k8s-master

[root@slavedb tmp]# hostname

k8s-node3

5. Write host entries into /etc/hosts

On server 192.168.20.40:

[root@docker02 ~]# cat /etc/hosts

127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4

::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

192.168.20.40 docker02

192.168.20.39 slavedb

On server 192.168.20.39 the same entries appear.

6. Extend the playbook to modify /etc/hosts

- name: modify etc hosts

shell: echo "{{ ansible_ens33['ipv4']['address'] }} {{ inventory_hostname }}" >>/etc/hosts

register: result

- debug: var=result

[root@docker02 ~]# ansible-playbook host.yml

7. Verify the updated /etc/hosts

[root@docker02 ~]# cat /etc/hosts

127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4

::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

192.168.20.40 docker02

192.168.20.39 slavedb

192.168.20.40 k8s-master

[root@slavedb tmp]# cat /etc/hosts | egrep -v "^$|^#" /etc/hosts

127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4

::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

192.168.20.40 docker02

192.168.20.39 slavedb

192.168.20.39 k8s-node3

Related reading

Write Playbook to Deploy an Etcd Cluster

Playbook for Bulk Docker Deployment

Playbook to Distribute Nginx Configuration Files