An example how to avoid race condition with lineinfile delegated to one host

lineinfile_delegation.yml

---
- hosts: all
  gather_facts: no
  
tasks:
  - name: Create a virtual machine on given ESXi hostname
    vmware_guest:
      hostname: "{{ vcenter_address }}"
      username: "{{ domain_user }}"
      password: "{{ domain_pass }}"
      datacenter: "{{ dc }}"
      validate_certs: no
      folder: Folder
      name: "{{ inventory_hostname }}"
      template: "{{ core_template }}"
      state: present
      guest_id: centos64Guest
      esxi_hostname: "{{ esxi }}"
      datastore: "{{ ds }}"
    delegate_to: localhost
    register: vm_deploy
    
  - name: Grouping by vm_deploy
    group_by:
      key: vm_deploy
    changed_when: no
    
  # Magic happens below, lineinfile will interate over all hosts grouped by vm deploy task and
  # construct lines based on hosts private variables
  # Task delegated to one host and should be run once per play
  - name: Updating cobler config template (ADD entries)
    lineinfile:      
      line: "{{ (item.split('.'))[0] }} {{ hostvars[item]['ip_private'] }} {{ hostvars[item]['vm_deploy']['instance']['hw_eth0']['macaddress'] }} {{ cobbler_profile }}"
      path: "/path/to/cobbler/template-{{ dc }}"
      backup: no
    register: cobler_config_add
    delegate_to: "{{ cobbler[dc] }}"
    become: yes
    with_items: "{{ groups['vm_deploy'] }}"
    run_once: yes