Pubkeys should be added to the root user as well.

roles/ubuntu_base/tasks/users.yml

@@ -13,3 +13,9 @@
     user: "{{ item.key }}"
     key: "{{ item.value.key }}"
   with_dict: "{{ users | default({}) }}"
+
+- name: "Add ssh authorized_keys to root user"
+  authorized_key:
+    user: "root"
+    key: "{{ item.value.key }}"
+  with_dict: "{{ users | default({}) }}"