On 1.3.2017 14:58, Alexander Bokovoy wrote:
On ke, 01 maalis 2017, Jan Cholasta wrote:
On 1.3.2017 14:05, Alexander Bokovoy wrote:
On ke, 01 maalis 2017, Jan Cholasta wrote:
On 1.3.2017 13:39, Martin Babinsky wrote:

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

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
of this list, we have decided that this information is no longer
to trust configuration and should be a part of the global config

Also we have purposefully cut down the API only to a raw
of the attribute using an option of `ipa config-mod`. The reasons
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
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
allowed in AD domain names.

I have discussed this with Jan and consulted the same document that
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?

Actually I would prefer something else than whitespace as a separator.
A ':' maybe?
or ',' or ';'. Any would work.

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
retrieve it and this signals that it should continue operate in usual

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

It doesn't have to be literally empty (LDAP character string syntaxes
don't allow it anyway IIRC), there can be a value which denotes an
empty list of domain (e.g. the separator alone).
I don't see *why* there should be this distinction. The deciding party
is SSSD. Whether this attirbute exists and empty or does not exist at
all does not change anything. Changing how SSSD interprets own defaults
depending on absense or emptiness of certain attribute in IPA config
object is not user friendly at all.

SSSD default behavior should stay the same whether it finds missing or
empty attribute because the attribute will not be known to older SSSD
anyway. Missing or empty attribute should, in my opinion, be equal to
older SSSD behavior.

"No value is set in configuration => use built-in default / some value
is set configuration => use the value" is perfectly user friendly and
pretty much common virtually everywhere I believe, much more so than
"empty value is set in configuration => ignore the value even if the
user deliberately set it empty and use the default value instead".
I'm not arguing with "no value is set in configuration -> use built-in
default". I do argue on having empty but present attribute because it
does not add anything useful for SSSD to decide on. And as it is not
adding anything useful, why there should be such difference at all?

This is the only question open I see in this design.

The list does not have to contain all available domains, therefore it can also be empty. When a domain is not present in the list, a fully qualified name must be used for users in that domain, therefore when the list is empty, fully qualified name must be used for users in all domains.

This might be useful to someone, and even if it wasn't, I still don't think it warrants making a (IMO counter-intuitive) special case out of the empty list.

Jan Cholasta

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