ansible_roles_webcluster/web_site.yml

---
- hosts: all
  roles:
    - web_base

- hosts: lb
  serial: "25%"
  max_fail_percentage: 40
  roles:
    - web_lb

- hosts: db
  serial: 1
  max_fail_percentage: 10
  roles:
    - web_db

- hosts: worker
  serial: 2
  max_fail_percentage: 20
  roles:
    - web_worker