hosts.ini
[group]
dbclient.example.com ip=x.x.x.x
db.example.com       ip=y.y.y.y


group_vars/group.yml
ansible_host: "{{ip}}"


playbook.yml
hosts: dbclient.example.com
tasks:
- name: 'Test hostname'
  command: 'hostname'
  delegate_to: db.example.com


expected output
changed: [dbclient.example.com -> db.example.com] => {
    "changed": true,
    ...
    "stdout": "db.example.com"
}

actual output
changed: [dbclient.example.com -> {{ip}}] => {
    "changed": true,
    ...
    "stdout": "dbclient.example.com"
}