Most playbooks and roles will make use of variables; these variables can be overridden in several ways. The simplest way is to create files in the host_vars and groups_vars folders, these allow you to override variables either based on the host or group membership, respectively. For this, perform the following steps:

1. Create a directory /etc/ansible/group_vars.
2. Create a file in group_vars named mons. Add the following in mons:

       a_variable: "foo"

3. Create a file in group_vars named osds. Add the following in osds:

       a_variable: "bar"

Variables follow a precedence order; you can also create an all file, which will apply to all groups. However, a variable of the same name that is in a more specific matching group will override it. The Ceph Ansible modules make use of this to allow you to have a set of default variables and then also allow you to specify different values for the specific roles.