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Just to illustrate the discussion, we have a bug fix that currently tries
to drop a FK between the federation and identity subsystems [1].

The previous fix for this bug (which has been merged and had the backport
abandoned) took advantage of the FK in order to cascade delete federated
users when a protocol or an identity provider is deleted [2].

[1] https://review.openstack.org/#/c/445505/
[2] https://review.openstack.org/#/c/420893/

On Wed, Apr 12, 2017 at 11:58 AM, Lance Bragstad <lbragstad at gmail.com>
wrote:

>
>
> 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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>
>
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-- 
Rodrigo Duarte Sousa
Senior Quality Engineer @ Red Hat
MSc in Computer Science
http://rodrigods.com
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