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Ansible config-download differences
Starting with the Queens release, it is possible to use Ansible to apply the overcloud configuration. In the Rocky release, this method is the new default behavior.
The feature is fully documented at ansible_config_download, while this page details the
differences to the deployer experience with config-download.
Ansible vs. os-collect-config
Previously, TripleO used an agent running on each overcloud node
called os-collect-config. This agent periodically polled
the undercloud Heat API for software configuration changes that needed
to be applied to the node.
os-collect-config ran os-refresh-config and
os-apply-config as needed whenever new software
configuration changes were detected. This model is a
"pull" style model given each node polled the Heat API
and pulled changes, then applied them locally.
With config-download, TripleO has switched to a
"push" style model. Ansible is run from a central
control node which is the undercloud. ansible-playbook is
run from the undercloud and software configuration changes are pushed
out to each overcloud node via ssh.
With the new model, os-collect-config,
os-refresh-config, and os-apply-config are no
longer used in a TripleO deployment. The os-collect-config
service is now disabled by default and won't start on boot.
Note
Heat standalone software deployments still rely on
os-collect-config. They are a type of deployment that can
be applied to overcloud nodes directly via Heat outside of the overcloud
stack, and without having to do a full stack update of the overcloud
stack.
These types of deployments are NOT typically used when doing TripleO.
However, if these deployments are being used in an environment to
manage overcloud nodes, then the os-collect-config service
must be started and enabled on the overcloud nodes where these types of
deployments are applied.
For reference, the Heat CLI commands that are used to create these types of deployments are:
openstack software config create ...
openstack software deployment create ...If these commands are not being used in the environment, then
os-collect-config can be left disabled.
Deployment workflow
The default workflow executed by
openstack overcloud deploy takes care of all the necessary
changes when using config-download. In both the previous and new
workflows, openstack overcloud deploy (tripleoclient) takes
care of automating all the steps through Mistral workflow(s). Therefore,
existing CLI scripts that called openstack overcloud deploy
will continue to work with no changes.
It's important to recognize the differences in the workflow to aid in understanding the deployment and operator experience. Previously, Heat was responsible for:
- (Heat) Creating OpenStack resources (Neutron networks, Nova/Ironic instances, etc)
- (Heat) Creating software configuration
- (Heat) Applying the created software configuration to the Nova/Ironic instances
With config-download, Heat is no longer responsible for the last item
of applying the created software configuration as
ansible-playbook is used instead.
Therefore, only creating the Heat stack for an overcloud is no longer all that is required to fully deploy the overcloud. Ansible also must be run from the undercloud to apply the software configuration, and do all the required tasks to fully deploy an overcloud such as configuring services, bootstrap tasks, and starting containers.
The new steps are summarized as:
- (Heat) Creating OpenStack resources (Neutron networks, Nova/Ironic instances, etc)
- (Heat) Creating software configuration
- (tripleoclient) Enable tripleo-admin ssh user
- (ansible) Applying the created software configuration to the Nova/Ironic instances
See ansible_config_download for details on the
tripleo-admin ssh user step.
Deployment CLI output
During a deployment, the expected output from
openstack overcloud deploy has changed. Output up to and
including the stack create/update is similar to previous releases. Stack
events will be shown until the stack operation is complete.
After the stack goes to CREATE_COMPLETE (or
UPDATE_COMPLETE), output from the steps to enable the
tripleo-admin user via ssh are shown.