systemd configuration lookups are lightweights and straightforward compared to ansible variables lookups rules : -- Understanding variable precedence

  Ansible does apply variable precedence, and you might have a use for it. Here is the order of precedence from least to greatest (the last listed variables override all other variables):

        1 command line values (for example, -u my_user, these are not variables)

        2 role defaults (defined in role/defaults/main.yml) 1

        3 inventory file or script group vars 2

        4 inventory group_vars/all 3

        5 playbook group_vars/all 3

        6 inventory group_vars/* 3

        7 playbook group_vars/* 3

        8 inventory file or script host vars 2

        9 inventory host_vars/* 3

        10 playbook host_vars/* 3

        11 host facts / cached set_facts 4

        12 play vars

        13 play vars_prompt

        14 play vars_files

        15 role vars (defined in role/vars/main.yml)

        16 block vars (only for tasks in block)

        17 task vars (only for the task)

        18 include_vars

        19 set_facts / registered vars

        20 role (and include_role) params

        21 include params

        22 extra vars (for example, -e "user=my_user")(always win precedence)

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that is a RedHat-isim