[Rdo-list] [OFI] data model reusing Foreman's AR models

[Petr Chalupa]

Hi guys,

After yesterdays IRC talk we (Marek and Petr) started to look at OFI 
models design. Unfortunately I haven't received any email with link to 
that so we jumped in quite late. Anyway we've tried to decode as much 
information as possible about staypuft model from etherpad [1]. Here's 
ER diagram we were able to construct from those information.

<see model A>

Our main concern is that we are recreating models that are already 
present in Foreman. We understand Astapor issue that it was very hard 
for user understand all Foreman specifics so now we try to do it 
Openstack way and use Foreman as provisioning and configuration backend. 
However we still think that we should built on top of existing and 
tested models and just create a new easy to use and intuitive UI.

inecas: +1 on reusing the Foreman model: the foreman model seems to have 
most of the things to support what is required, building something 
custom means:
   * duplication of what is already there
   * writing throw-away code, that nobody except the OFI itself will 
use: the power of Foreman is in the community: building it on the 
Foreman model (and enhancing it when needed) means the same work will be 
used outside of OFI with all the benefits that come with it
I would like to avoid doing that, especially when it doesn't seem that 
much work to use the existing model

So what we propose is following DB schema:

<see model B>

Each deployment is contained under an Organization for separation. Which 
also means that same Foreman instance could be normally used when user 
leaves the wizard.

Left side is ER model right side is representing relationships between 
Hostgroups instances. The one called 'Deploy' is lets say an common 
parent Hostgroup for all other hostgroups in the deployment. 'Deploy' 
allows sharing of configuration to the other hostgroups. Other 
hostgroups are representing Roles (like controller, compute, etc.)

Basically we'd map:
OpenStackDeployment -> Organization
OpenStackLayout -> organization's parameter
OpenStackRole -> Hostgroup (*)
OpenStackService -> N/A (at least for April)
OpenStackSeviceParam -> LookupKey (aka Smart Variable)
OpenStackDeployService -> N/A
OpenStackDeployServiceParam -> LookupKey (aka Smart Variable Value)
OpenStackDeployRole -> assignment of Host to Hostgroup (*)

At the moment, the only thing that's missing is that Foreman 1.4.1 does 
not allow us to set one hostgroup to be used in two parent hostgroups 
(one service in two roles). This is going to change in 1.5 when 
ConfigRoles will be merged. We suppose to use quickstack modules for 
April version so we still have just puppet classes on role level (not on 
service level) and therefore we won't allow user to customize services 
in roles. Since we need this post April we can stick with current 
Foreman model. Later we could either back-port ConfigRoles or base on 
newer Foreman.

Benefits we see by reusing foreman models
+ we save work on need to model everything again
+ we save work on writing logic that will copy all (Deploy)Service/Role 
(Deploy)ServiceParameters values to Hostgroup/LookupKey/LookupValue
+ ability to turn off the wizard plugin (something like removing the 
training wheels) and keeping the Foreman instance still usable

Cons
- people may spend some time to better understand existing Foreman code
inecas: that should be under Pros, and by people I don't mean the actual 
users of OFI, but its developers

Potential concerns we understood from yesterday
1. too foreman specific
2. need of doing some business logic before Deploy is triggered
3. writing some easy UI around existing models is bigger pain that 
creating new objects from scratch
4. to able to delay host provisioning until whole deployment is configured

Our answers to those
1. this is just about building new UI that we'll need anyway and 
re-labeling (we already have Smart Variable which in fact is LookupKey 
model), we could use STI or composition to modify Foreman objects 
behavior if they are too restricting
2. It's easy to extend Dynflow process with a plugin injecting any 
additional steps into the deployment process.
3. if this really becomes a problem we could always wrap existing models 
by some other classes
4. If the hosts are kept in unmanaged state nothing gets applied to 
them. Until orchestration takes over and switches them to managed state.

Are we sure that we need to allow user to prepare changes to an 
existing-deployment-configuration and then apply them all at the same 
time in April? I think we can postpone this for later and keep Foreman's 
behavior for now that changes made to a hostgroup are immediately applied.

[1]: http://etherpad.corp.redhat.com/staypuft-model-design-notes

Looking forward to your feedback Petr and Marek.

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