Appendix D: Customizing host and service layouts

Appendix D: Customizing host and service layouts

The default layout of containers and services in OpenStack-Ansible (OSA) is determined by the /etc/openstack_deploy/openstack_user_config.yml file and the contents of both the /etc/openstack_deploy/conf.d/ and /etc/openstack_deploy/env.d/ directories. You use these sources to define the group mappings that the playbooks use to target hosts and containers for roles used in the deploy.

  • You define host groups, which gather the target hosts into inventory groups, through the /etc/openstack_deploy/openstack_user_config.yml file and the contents of the /etc/openstack_deploy/conf.d/ directory.
  • You define container groups, which can map from the service components to be deployed up to host groups, through files in the /etc/openstack_deploy/env.d/ directory.

To customize the layout of the components for your deployment, modify the host groups and container groups appropriately before running the installation playbooks.

Understanding host groups

As part of the initial configuration, each target host appears either in the /etc/openstack_deploy/openstack_user_config.yml file or in files within the /etc/openstack_deploy/conf.d/ directory. The format used for files in the conf.d/ directory is identical to the syntax used in the openstack_user_config.yml file.

In these files, the target hosts are listed under one or more headings, such as shared-infra_hosts or storage_hosts, which serve as Ansible group mappings. These groups map to the physical hosts.

The haproxy.yml.example file in the conf.d/ directory provides a simple example of defining a host group (haproxy_hosts) with two hosts (infra1 and infra2).

The swift.yml.example file provides a more complex example. Here, host variables for a target host are specified by using the container_vars key. OpenStack-Ansible applies all entries under this key as host-specific variables to any component containers on the specific host.


To manage file size, we recommend that you define new inventory groups, particularly for new services, by using a new file in the conf.d/ directory.

Understanding container groups

Additional group mappings are located within files in the /etc/openstack_deploy/env.d/ directory. These groups are treated as virtual mappings from the host groups (described above) onto the container groups, that define where each service deploys. By reviewing files within the env.d/ directory, you can begin to see the nesting of groups represented in the default layout.

For example, the shared-infra.yml file defines a container group, shared- infra_containers, as a subset of the all_containers inventory group. The shared- infra_containers container group is mapped to the shared-infra_hosts host group. All of the service components in the shared-infra_containers container group are deployed to each target host in the shared-infra_hosts host group.

Within a physical_skel section, the OpenStack-Ansible dynamic inventory expects to find a pair of keys. The first key maps to items in the container_skel section, and the second key maps to the target host groups (described above) that are responsible for hosting the service component.

To continue the example, the memcache.yml file defines the memcache_container container group. This group is a subset of the shared-infra_containers group, which is itself a subset of the all_containers inventory group.


The all_containers group is automatically defined by OpenStack-Ansible. Any service component managed by OpenStack-Ansible maps to a subset of the all_containers inventory group, directly or indirectly through another intermediate container group.

The default layout does not rely exclusively on groups being subsets of other groups. The memcache component group is part of the memcache_container group, as well as the memcache_all group and also contains a memcached component group. If you review the playbooks/memcached-install.yml playbook, you see that the playbook applies to hosts in the memcached group. Other services might have more complex deployment needs. They define and consume inventory container groups differently. Mapping components to several groups in this way allows flexible targeting of roles and tasks.

Customizing existing components

Deploying directly on hosts

To deploy a component directly on the host instead of within a container, set the is_metal property to true for the container group in the container_skel section in the appropriate file.

The use of container_vars and mapping from container groups to host groups is the same for a service deployed directly onto the host.


The cinder-volume component is deployed directly on the host by default. See the env.d/cinder.yml file for this example.

Omit a service or component from the deployment

To omit a component from a deployment, you can use one of several options:

  • Remove the physical_skel link between the container group and the host group by deleting the related file located in the env.d/ directory.
  • Do not run the playbook that installs the component. Unless you specify the component to run directly on a host by using the is_metal property, a container is created for this component.
  • Adjust the affinity to 0 for the host group. Similar to the second option listed here, Unless you specify the component to run directly on a host by using the``is_metal`` property, a container is created for this component.

Deploy existing components on dedicated hosts

To deploy a shared-infra component to dedicated hosts, modify the files that specify the host groups and container groups for the component.

For example, to run Galera directly on dedicated hosts, you would perform the following steps:

  1. Modify the container_skel section of the env.d/galera.yml file. For example:

          - db_containers
          - galera
          is_metal: true


    To deploy within containers on these dedicated hosts, omit the is_metal: true property.

  2. Assign the db_containers container group (from the preceding step) to a host group by providing a physical_skel section for the host group in a new or existing file, such as env.d/galera.yml. For example:

          - all_containers
          - hosts
  3. Define the host group (db_hosts) in a conf.d/ file (such as galera.yml). For example:



    Each of the custom group names in this example (db_containers and db_hosts) are arbitrary. Choose your own group names, but ensure the references are consistent among all relevant files.

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