Run kolla-ansible limit on compute node cause creating Nova databases

I would like to let kolla-ansible run plays for compute nodes only without touching existing control nodes(which are not deployed by kolla-ansible).
But if I run kolla-ansible with --limit compute_node, The ansible tasks of creating Nova databases still run which seems wrong, and I got failure like the following if I erase all control nodes from inventory file.

TASK [nova : include] ***********************************************************************************************************************************************************
included: /home/huzhj/daisy4nfv_inner_repo/daisy4nfv/kolla-ansible/ansible/roles/nova/tasks/bootstrap.yml for tanabata

TASK [nova : Creating Nova databases] *******************************************************************************************************************************************
fatal: [tanabata]: FAILED! => {"failed": true, "msg": "list object has no element 0"}

NO MORE HOSTS LEFT **************************************************************************************************************************************************************
        to retry, use: --limit @/home/huzhj/daisy4nfv_inner_repo/daisy4nfv/kolla-ansible/ansible/site.retry

PLAY RECAP **********************************************************************************************************************************************************************
localhost : ok=1 changed=0 unreachable=0 failed=0
tanabata : ok=30 changed=19 unreachable=0 failed=1

Command failed ansible-playbook -i ./ansible/inventory/multinode -e @/etc/kolla/globals.yml -e @/etc/kolla/passwords.yml -e CONFIG_DIR=/etc/kolla -e action=deploy /home/huzhj/daisy4nfv_inner_repo/daisy4nfv/kolla-ansible/ansible/site.yml

My inventory file is like this:

[control]

[network]

[compute]
tanabata

[monitoring]

[storage]

[deployment]
localhost ansible_connection=local
...

I took a look at ansible/roles/nova/tasks/deploy.yml, it shows that bootstrap.yml runs for both nova-api and compute groups, why we need to do like this? I thought bootstrap.yml is for nova-api group only, isn't it?

- include: bootstrap.yml
  when: inventory_hostname in groups['nova-api'] or
        inventory_hostname in groups['compute']