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On Wed, Apr 12, 2017 at 9:28 AM, David Stanek <dstanek at dstanek.com> wrote:

> [tl;dr I want to remove the artificial restriction of not allowing FKs
> between
> subsystems and I want to stop FK enforcement in code.]
>
> The keystone code architecture is pretty simple. The data and
> functionality are
> divided up into subsystems. Each subsystem can be configured to use a
> different
> backend datastore. Of course, there are always exceptions to the rule like
> how
> the federation and identity subsystems are highly coupled in the data
> model.
>
> On the surface this flexible model sounds good, but there are some
> interesting
> consequences. First, you can't tell from looking at the data model that
> there
> actually is a lot of coupling between the subsystems. So instead of
> looking at
> our sqlalchemy models to see relationships, we must look throughout the
> code
> for where a particular primary key is used and look for enforcement.
> (Hopefully
> we enforce it in all of the right places.) Additionally, a DBA/data
> architect/
> whenever can't see the relationship at all by looking at the database.
>
> Second, this has polluted our code and causes erroneous API errors. We
> have added
> lots of get_*() calls in our code that checks for the existence of IDs in
> another subsystem. In some cases we probably don't do the check and thus
> would
> allow bad data to be stored. The check often causes 404s instead of 400s
> when
> bad data is provided.
>

Having these cleaned up would be awesome. I imagine we'd also see some sort
of performance benefit as a result, too.


>
> So I'd like us to be more deliberate in defining which parts of the data
> model
> are truly independent and a separate backend datastore would make sense.
> For
> instance, we know we want to support LDAP for identity (although this
> still puts
> identity info into a SQL database) and catalog is very isolated from the
> rest of
> the data model.
>
> As a side effect this means that if deployers wished to use a separate
> backend
> for something they would need to also implement it for the other highly
> coupled
> subsystems. They would also have to provide any FK enforcement that their
> own
> datastore does not provide.
>

So for deployers, this would mean that if today they only deploy keystone
backed with LDAP for *only* identity, tomorrow they will have to ensure
that LDAP has all the proper things for other subsystems that use to have
an in-code constraint with identity (i.e. assignment). I wonder how many
folks that would be? What would an upgrade look like for deployments
wishing to stick to LDAP? I imagine we'd be raising the bar for that
particular upgrade.


>
> Thoughts?
>
> --
> david stanek
> web: https://dstanek.com
> twitter: https://twitter.com/dstanek
>
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