How do I use Ansible to add an IP to a Linux hosts file on 18 VMs that iterates from 10.x.x.66..10.x.x.83

So, I have a playbook using a hosts file template to update or revert hosts files on 18 specific Linux VMs. The entry which goes at the end of the file looks like:

10.x.x.66 fooconnect

This above example would be on the 1st of 18 VMs, the 18th VM would look like:

10.x.x.83 fooconnect

Normally, that hostname resolves to a VIP. However, we found during some load testing that it may be beneficial to point each front-end VM to a back-end VM directly. So, my goal is to have a playbook that can update what the hostname resolves to with the above mentioned range, or revert it back to the VIP (reverting back is done using a template only--this part works fine).

What I am unsure about is how to implement this in Ansible. Is there a way to loop through the IPs using jinja2 template "for loops?" Or maybe using lineinfile with some loop magic?

Here is my Ansible role example. For the moment I am using a dirty shell command to create my IP list...open to suggestions for a better way to implement this.

- name: Add a line to a hosts file using a template
  template:
    src: "{{ srcfile }}"
    dest: "{{ destfile }}"
    owner: "{{ own_var }}"
    group: "{{ grp_var }}"
    mode: "{{ mode_var }}"
    backup: yes

- name: Get the IPs
  shell: "COUNTER=66;for i in {66..83};do echo 10.x.x.$i;((COUNTER++));done"
  register: pobs_ip

- name: Add a line
  lineinfile:
    path: /etc/hosts
    line: "{{item}}    fooconnect"  #Ideally would want "item" to just be one IP and not 
    insertafter: EOF                #the entire list as it would be like this.
  loop: "{{pobsips}}"

VARs file:

pobsips:
  - "{{pobs_ip.stdout}}"

Solution

Instead of using a shell task, we can improvise it and create the range of IP addresses using set_fact with range. Once we have the range of IP addresses in a "list", we can loop lineinfile with that and achieve this.

Example:

    - name: create a range of IP addresses in a variable my_range
      set_fact:
        my_range: "{{ my_range|default([]) + [ '10.1.1.' ~ item ] }}"
      loop: "{{ range(66, 84)|list }}"
    - name: Add a line to /etc/hosts
      lineinfile:
        path: /etc/hosts
        line: "{{ item }} fooconnect"
        insertafter: EOF
      loop: "{{ my_range }}"

Updated answer:

There is another approach if we want to append only 1 line into the /etc/hosts file of each host with incrementing IP addresses.

For this we can use the ipmath of ipaddr filter to get the next IP address for given IP address.
Use ansible_play_hosts to get the list of hosts on which play is running
Set an index variable index_var and when condition to update file only when the ansible_hostname or inventory_hostname matches.
Run playbook serially and only once on a host per run using serial and run_once flags.

Let's consider an example inventory file like:

[group_1]
host1
host2
host3
host4
...

Then in playbook:

- hosts: group_1
  serial: 1

  vars:
    start_ip: 10.1.1.66

  tasks:
    - name: Add a line to /etc/hosts
      lineinfile:
        path: "/tmp/hosts"
        line: "{{ start_ip|ipmath(my_idx) }} fooserver"
        insertafter: EOF
      loop: "{{ ansible_play_hosts }}"
      loop_control:
        index_var: my_idx
      run_once: true
      when: item == inventory_hostname