[Freeipa-devel] Please review: V4/AD user short names design draft

[Martin Babinsky]

Alexander,

thank you for your comments. Replies inline:

On 02/28/2017 01:48 PM, Alexander Bokovoy wrote:
> On ti, 28 helmi 2017, Martin Babinsky wrote:
>> Hello list,
>>
>> I have put together a draft of design page describing server-side
>> implementation of user short name -> fully-qualified name resolution.[1]
>>
>> In the end I have taken the liberty to change a few aspects of the
>> design we have agreed on before and I will be grad if we can discuss
>> them further.
>>
>> Me and Honza have discussed the object that should hold the domain
>> resolution order and given the fact that IPA domain can also be a part
>> of this list, we have decided that this information is no longer bound
>> to trust configuration and should be a part of the global config instead.
>>
>> Also we have purposefully cut down the API only to a raw manipulation
>> of the attribute using an option of `ipa config-mod`. The reasons for
>> this are twofold:
>>
>>  * the developer resources are quite scarce and it may be good to
>> follow YAGNI[2] principle to implement the dumbest API now and not to
>> invest into more high-level interface unless there is a demand for it
>>
>>  * we can imagine that the manipulation of the domain resolution order
>> is a rare operation (ideally only once all trusts are established), so
>> I am not convinced that it is worth investing into designing
>> higher-level API
>>
>> I propose we first develop the "dumber" parts first to unblock the
>> SSSD part. If we have spare cycle afterwards then we can design and
>> implement more bells-and-whistles afterwards.
> Looks mostly OK, but there are few comments I have:
>
> - I do not see you mention how validation of the
>  ipaDomainResolutionOrder is done. This is important to avoid hard to
>  debug issues because SSSD will ignore domains it doesn't know about.
>

The validation is described in a Design section as follows:

"""
Finally, any modification of the domain resolution order must ensure 
that each of the specified domain names corresponds either to that of 
FreeIPA domain or to one of the trusted AD domains stored in LDAP 
backend. In the case of trusted domains, the domain must not be marked 
as disabled.
"""

Is this sufficient or is a more thorough validation required? Shall I 
split the whole section into sub-sections for easier navigation?

> - Space separator initially caused me to look up DNS RFCs as strictly
>  speaking domain names can contain any 8-bit octet (while host names
>  should follow LDH rule). But then [1] does explicitly say space is not
>  allowed in AD domain names.
>

I have discussed this with Jan and consulted the same document that you 
cited, that's why I have arrived to the conclusion to use whitespace as 
separator. Jakub/Fabiano, is this ok with the way SSSD decodes domain 
names or should we consider other options to avoid breakage with more 
exotic domain names?

> - "If ipaDomainResolutionOrder is empty then *all* users must use fully
>  qualified names." This is not correct with regards to the current
>  behavior. I think we should change this to "if
>  ipaDomainResolutionOrder is empty, then standard SSSD configuration
>  logic applies on each client." This would make current behavior
>  compatible with either empty or ipaDomainResolutionOrder value of
>  a single IPA domain name.
>

I have considered a empty attribute value to be a distinct state from 
the missing attribute and assigned a different semantic meaning to it.

The reasoning is as follows: if the attribute is not set, SSSD will not 
retrieve it and this signals that it should continue operate in usual way.

If the attribute is present but is empty, the semantics change slightly 
as now we consider *no* domains during short name resolution (extension 
of the missing domain behavior to the case of all domains are missing 
from list).

That is however open to discussion and I think we can even get away from 
this by letting SSSD guys to decide how to handle this case.

> - There are typos in the page.
>

I know there was not much proofreading involved in this iteration. I 
have already tried to fix them.

> [1]
> https://support.microsoft.com/en-us/help/909264/naming-conventions-in-active-directory-for-computers,-domains,-sites,-and-ous
>
>
>


-- 
Martin^3 Babinsky