In order to run instances, OpenStack Compute needs to be aware of the physical resources on which to run the instances. As OpenStack has grown and matured over time, the process for adding a host has also grown with it. OpenStack-Ansible provides a very convenient and consistent method for adding new compute hosts which allows you to scale your environment as your needs grow. A compute host runs the nova-compute service and the hypervisor that spawns the appropriate instance type requested.
In order to add a compute host to an OpenStack cluster using openstack-ansible, you will need the following information:
- The IP address of the host
- SSH access to the host
- The SSH key from your deployment host
- Access to the deployment host
The values used in our example are as follows:
- Compute host:
172.29.236.15 - Deployment host:
controller-01.cook.book
We assume that your environment was already installed using OpenStack-Ansible as described in Chapter 1, Installing OpenStack with Ansible.
To install and configure an additional compute host using openstack-ansible, carry out the following steps:
- From the deployment host, add the additional compute host to the
/etc/openstack_deploy/openstack_user_config.ymlfile, as shown in the following example:compute_hosts: compute-01: ip: 172.29.236.13 compute-02: ip: 172.29.236.14 compute-03: ip: 172.29 236.15 - Run
setup-hosts.yml, limiting the tasks to justcompute-03:cd /opt/openstack-ansible/playbooks openstack-ansible setup-hosts.yml --limit compute-03
- Have Ansible gather facts about the new host:
ansible nova_all -m setup -a 'filter=ansible_local gather_subset="!all"' - Simply run
os-nova-install.ymlto install and configurenova-computeon our new compute host:openstack-ansible os-nova-install.yml --limit compute-03 - Confirm the new hypervisor by running the following commands on any of the controller servers (as they run the utility container):
lxc-attach --name $(lxc-ls -1 | grep utility) source openrc openstack hypervisor list
This should bring back output like the following:
The /etc/openstack_deploy/openstack_user_config file provides mappings of roles to hosts in our environment. Adding the IP address for compute-03.cook.book to the compute_hosts stanza, informs the openstack-ansible command to apply the packages, settings, and so forth to the new host. It also adds any required configuration to the remainder of your environment.
Tip
A full discussion of the Openstack-Ansible playbooks is beyond the scope of this book. For additional information on the playbooks and how they operate, you can review their documentation here: https://docs.openstack.org/project-deploy-guide/openstack-ansible/pike/