[389-devel] One Way AD Sync

[Nathan Kinder]

Please review these design notes for implementing one way AD sync.  In 
particular, I'm concerned about the possible inconsistencies that can 
arise from directly modifying a synced entry on the DS side.  Does using 
access control seem sufficient for avoiding these inconsistencies?

If these notes look OK, I'll get everything posted up on the 389 wiki.

Thanks,
-NGK

One Way Sync

Some deployments would prefer that AD sync is only performed in one 
direction.  More specifically, updates will be pulled from AD, but 
changes to DS will not be pushed back to AD.  Ideally, one would 
restrict direct updates to synchronized entries in DS by configuring 
access control.

To implement one-way sync, we need to add a new configuration attribute 
to the sync agreement entry.  This attribute will be named "oneWaySync" 
and will default to "false" if it is not specified to maintain backwards 
compatibility.  When this attribute is set to "true", updates will only 
go in the AD->DS direction.

If one way sync is enabled and changes are made to a synced entry on the 
DS side, a replication session with AD will be started.  In this 
session, we will not send any updates, but we will send the Dirsync 
control to AD to pull any updates.  This will result in an inconsistency 
in the modified entry between AD and DS.  This inconsistency will be 
resolved the next time any update is made to the entry on the AD side 
since we compare the entire entry between AD and DS when we receive a 
change via Dirsync.  To avoid these inconsistencies, it is recommended 
to not allow direct updates to synced attributes in entries on the DS side.

Another inconsistency that can occur is if a synced entry is directly 
deleted from DS.  This deletion is not sent to AD.  In this case, an 
update to the entry on the AD side will result in the entry being added 
back to DS.  The direct deletion of synced entries on the DS side should 
be avoided to prevent these inconsistencies.

Inside of the replication plug-in, we simply skip sending updates in 
both the total and incremental replication protocol sessions when using 
a one way sync agreement.  We don't want to change the RUV 
implementation for a one way sync agreement, so we will just 
fast-forward the RUV that we maintain for the AD system as if we had 
successfully sent the changes.