ansible conditional notes

check if first node in group.yaml

---
- name: do stuff only if first member in a group
  command: echo "hello"
  when: groups.some_group[0] == inventory_hostname

when check for OS and version.yaml

---
- name: do stuff only if RHEL6 or CentOS6
  command: 
  when: ansible_os_family == "RedHat" and ansible_lsb.major_release|int >= 6

when in groups.yaml

# group_names is a magic variable, list of groups that a host is a membeer of

- name: some module
  file:
  when: "'app1' in group_names"