Re: (ITS#6531) Modify updateref to generate referrals on the backend

[hyc@symas.com]

masarati@aero.polimi.it wrote:
>> Full_Name: Ryan Steele
>> Version: 2.4.18
>> OS: Ubuntu Server
>> URL: ftp://ftp.openldap.org/incoming/
>> Submission from: (NULL) (207.106.239.81)
>>
>>
>> Per conversation on the #openldap IRC channel on Freenode with Howard Chu,
>> it
>> has been deemed appropriate to modify the behavior of updateref to answer
>> referrals on the backend.  This would allow one to use updateref to
>> automatically chase referrals for individual backends, instead of it being
>> all
>> or nothing.  Here is the tail end of the channel conversation:
>>
>>
>> <hyc>  when you configure an updateref on a backend, that referral is only
>> generated in the frontend so putting the overlay on the database, misses
>> it...
>>
>> <rgsteele>  Well, I am intending to set an updateref on that backend
>>
>> <hyc>  then you have a problem
>>
>> <rgsteele>  Hm, so you can't do automatic referrals on individual backends
>> then?
>>
>> <rgsteele>  That was my original question, or at least the intent of it.
>>
>> <hyc>  not using updateref, no
>>
>> <rgsteele>  Does your response imply there's another way?
>>
>> <hyc>  probably we should fix updateref to be generated at the backend
>> level
>>
>> <rgsteele>  That would be good - I'd be happy to write tests or something
>> to help
>> with that.
>>
>> <hyc>  the "other way" is the normal referral mechanism - using referral
>> entries
>> inside a database
>>
>> <hyc>  but like I said, updateref is a relic, we've carried it forward
>> without
>> really adapting it
>>
>> <hyc>  probably should file an ITS about this
>>
>> <rgsteele>  Interesting, I wasn't aware of that method. I'll have to do
>> some
>> research on that - thanks! Also, is there anything I can do to help get
>> the
>> process of fixing updateref to generate referrals on the backend?
>>
>> <rgsteele>  I can file the ITS if you like?
>>
>> <hyc>  go ahead
>
> It is correct that referrals are generated by the frontend, but the
> frontend uses information contained in the updateref of each database.
> The slapo-chain needs to be global, in order to intercept those referrals.
>
> Although redesigning referral generation in slapd could streamline things,
> I don't quite see what issues can't be addressed using a global instance
> of slapo-chain.  You can configure referral chasing differently for
> different domains using the chain-uri directive.  I favor fixing only
> what's actually broken.

The request revolves around having different behavior for different databases. 
With a global slapo-chain you cannot turn off referral chasing; URIs that are 
not explicitly configured will still be chased.

Also in terms of logical abstraction the current behavior is wrong; the 
frontend should of course generate the default_referral responses but 
updateref is a per-backend item and should be generated at the backend layer. 
Ideally this would all have been fixed to behave correctly by moving all 
replication support into an overlay, where it properly belongs. As an interim 
step it would be trivial to write an updateref overlay that supersedes the 
current updateref behavior.

-- 
   -- Howard Chu
   CTO, Symas Corp.           http://www.symas.com
   Director, Highland Sun     http://highlandsun.com/hyc/
   Chief Architect, OpenLDAP  http://www.openldap.org/project/