tripleo-docs/deploy-guide/source/features/composable_services.rst

Deploying with Composable Services

TripleO offers the option of deploying with a user-defined list of services per role (where "role" means group of nodes, e.g "Controller", and "service" refers to the individual services or configurations e.g "Nova API").

Deploying with custom service lists

Each role to be used in the deployment is defined in a roles_data.yaml file. There is a sample file in /usr/share/openstack-tripleo-heat-templates, or the tripleo-heat-templates git repository. Additional example roles are located in the /usr/share/openstack-tripleo-heat-templates/roles directory and can be used to create a custom roles_data.yaml file. See custom_roles for additional usage details.

The data in roles_data.yaml is used to set the defaults for per-role parameters e.g ControllerServices. These defaults can be overridden via environment files, e.g:

cat > keystone_only_params.yaml << EOF

parameter_defaults:
  ControllerServices:
    - OS::TripleO::Services::Keystone
    - OS::TripleO::Services::RabbitMQ
    - OS::TripleO::Services::HAproxy
    - OS::TripleO::Services::MySQL
    - OS::TripleO::Services::Keepalived
  ComputeCount: 0
EOF

The example above overrides the default list of services, and instead deploys Keystone and the services it requires. It also sets the ComputeCount to zero to enable a minimal "keystone only" deployment on a single node.

You can then pass the environment file on deployment as follows:

openstack overcloud deploy -e keystone_only_params.yaml

The same approach can be used for any role.

Warning

While considerable flexibility is available regarding service placement with these interfaces, the flexible placement of pacemaker managed services is only available since the Ocata release.

Warning

In general moving control-plane services to the Compute role is not recommended, as the compute nodes require a different upgrade lifecycle and thus control-plane services on this role may present problems during major upgrades between releases.