Example ansible playbook to access facts from a group of hosts from another host

example.yml

---
# Execute using ansible-playbook -i hosts example.yml
- hosts: web
  gather_facts: yes

- hosts: db
  gather_facts: no # optional; speed optimization
  tasks:
    - name: Display addresses of all web hosts
    - debug: msg={{ hostvars[item].ansible_eth0.ipv4.address }}
      with_items: groups['web']

hosts

[db]
localhost
# Put your database hosts here

[web]
localhost
# Put your web hosts here