We need to make one change, the droplet role, which can be found at roles/droplet/tasks/main.yml; this change takes the dynamically assigned IP address and adds it to our droplets group of hosts. To do this, replace the following task:

- name: "print the IP address of the droplet" 
  debug:
    msg: "The IP of the droplet is {{ droplet_ip }}"

Replace it with the following task:

- name: add our droplet to a host group for use in the next step
  add_host:
    name: "{{ droplet_ip }}"
    ansible_ssh_host: "{{ droplet_ip }}"
    groups: "droplets"

As you can see, this takes the droplet_ip variable and adds a host using the add_host module to the group.