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):

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

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

      inventory file or script group vars 2

      inventory group_vars/all 3

      playbook group_vars/all 3

      inventory group_vars/* 3

      playbook group_vars/* 3

      inventory file or script host vars 2

      inventory host_vars/* 3

      playbook host_vars/* 3

      host facts / cached set_facts 4

      play vars

      play vars_prompt

      play vars_files

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

      block vars (only for tasks in block)

      task vars (only for the task)

      include_vars

      set_facts / registered vars

      role (and include_role) params

      include params

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

In general, Ansible gives precedence to variables that were defined more recently, more actively, and with more explicit scope. Variables in the defaults folder inside a role are easily overridden. Anything in the vars directory of the role overrides previous versions of that variable in the namespace. Host and/or inventory variables override role defaults, but explicit includes such as the vars directory or an include_vars task override inventory variables.