Open Stack

If you haven't followed the "Configuration management with etcd /
confd" thread [1], Doug found out that using confd to generate
configuration files wouldn't work for the Cinder case where we don't
know in advance of the deployment what settings to tell confd to look
at.
We are still looking for a generic way to generate *.conf files for
OpenStack, that would be usable by Deployment tools and operators.
Right now, Doug and I are investigating some tooling that would be
useful to achieve this goal.

Doug has prototyped an Ansible role that would generate configuration
files by consumming 2 things:

* Configuration schema, generated by Ben's work with Machine Readable
Sample Config.
  $ oslo-config-generator --namespace cinder --format yaml > cinder-schema.yaml

It also needs: https://review.openstack.org/#/c/474306/ to generate
some extra data not included in the original version.

* Parameters values provided in config_data directly in the playbook:
   config_data:
     DEFAULT:
       transport_url: rabbit://user:password@hostname
       verbose: true

There are 2 options disabled by default but which would be useful for
production environments:
* Set to true to always show all configuration values: config_show_defaults
* Set to true to show the help text: config_show_help: true

The Ansible module is available on github:
https://github.com/dhellmann/oslo-config-ansible

To try this out, just run:
  $ ansible-playbook ./playbook.yml

You can quickly see the output of cinder.conf:
    https://clbin.com/HmS58


What are the next steps:

* Getting feedback from Deployment Tools and operators on the concept
of this module.
  Maybe this module could replace what is done by Kolla with
merge_configs and OpenStack Ansible with config_template.
* On the TripleO side, we would like to see if this module could
replace the Puppet OpenStack modules that are now mostly used for
generating configuration files for containers.
  A transition path would be having Heat to generate Ansible vars
files and give it to this module. We could integrate the playbook into
a new task in the composable services, something like
  "os_gen_config_tasks", a bit like we already have for upgrade tasks,
also driven by Ansible.
* Another similar option to what Doug did is to write a standalone
tool that would generate configuration, and for Ansible users we would
write a new module to use this tool.
  Example:
      Step 1. oslo-config-generator --namespace cinder --format yaml >
cinder-schema.yaml (note this tool already exists)
      Step 2. Create config_data.yaml in a specific format with
parameters values for what we want to configure (note this format
doesn't exist yet but look at what Doug did in the role, we could use
the same kind of schema).
      Step 3. oslo-gen-config -i config_data.yaml -s schema.yaml >
cinder.conf (note this tool doesn't exist yet)

      For Ansible users, we would write an Ansible module that would
take in entry 2 files: the schema and the data. The module would just
run the tool provided by oslo.config.
      Example:
          - name: Generate cinder.conf
            oslo-gen-config: schema=cinder-schema.yaml
                                       data=config_data.yaml


Please bring feedback and thoughts, it's really important to know what
folks from Installers think about this idea; again the ultimate goal
is to provide a reference tool to generate configuration in OpenStack,
in a way that scales and is friendly for our operators.

Thanks,

[1] http://lists.openstack.org/pipermail/openstack-dev/2017-June/118176.html
-- 
Emilien Macchi