ansible - example of dynamic even/odd groups

play.yml

# requirement
# given 2 groups (A and B), target 50% of each for code deploy
- hosts: localhost
  tasks:
  
    # this might need to be group_by or add_host
    - set_fact: 
        even: "{{ groups['groupA'][::2] | union(groups['groupB'][::2] }}"
        odd: "{{ groups['groupA'][1::2] | union(groups['groupB'][1::2] }}"


- hosts: even
  roles:
    - deploy something

- hosts: odd
  roles:
    - deploy something
    
# it may also be possible to do
#- hosts: even;odd
#  serial: 50%