Role dependencies

I am using the roles + site.yml recommended setup.
Most, but not all boxes run telegraf (a stats collector), which is defined as an inventory group as a (tagged) role in site.yml.

In my Redis role, if the current host has the telegraf role I’d like to add a file a folder (so Telegraf will pick it up) and refresh the telegraf service.
Here is where it gets tricky - I would basically call out to a different role - what is the way to do this in Ansible?

I've used role dependencies to address a similar requirement (collectd
in our case).

http://docs.ansible.com/ansible/playbooks_roles.html#role-dependencies

If you make the telegraf role a dependency of the redis role, you'll
have access to vars
set by the telegraf role as well as its handlers by the time the redis
role runs.

you just a need a file roles/redis/meta/main.yml that looks like this: