---
- name: 'MONITORING | Host type: lxc_vm'
  set_fact:
    monitoring_entry: >
      {{ { 'address': ansible_host,
           'host_type': 'lxc_vm' } }}

- name: 'MONITORING | Append host'
  set_fact:
    monitoring_facts: >
      {{ hostvars[monitoring_host]['monitoring_facts']
          | default({})
          | combine({host_fqdn: monitoring_entry}) }}
  delegate_facts: true
  delegate_to: '{{ monitoring_host }}'
...