SLAPO-DDS(5)                  File Formats Manual                 SLAPO-DDS(5)

       slapo-dds - Dynamic Directory Services overlay to slapd


       The dds overlay to slapd(8) implements dynamic objects as per RFC 2589.
       The name dds stands for Dynamic Directory Services.  It allows to
       define dynamic objects, characterized by the dynamicObject objectClass.

       Dynamic objects have a limited lifetime, determined by a time-to-live
       (TTL) that can be refreshed by means of a specific refresh extended
       operation.  This operation allows to set the Client Refresh Period
       (CRP), namely the period between refreshes that is required to preserve
       the dynamic object from expiration.  The expiration time is computed by
       adding the requested TTL to the current time.  When dynamic objects
       reach the end of their lifetime without being further refreshed, they
       are automatically deleted.  There is no guarantee of immediate
       deletion, so clients should not count on it.

       Dynamic objects can have subordinates, provided these also are dynamic
       objects.  RFC 2589 does not specify what the behavior of a dynamic
       directory service should be when a dynamic object with (dynamic)
       subordinates expires.  In this implementation, the lifetime of dynamic
       objects with subordinates is prolonged until all the dynamic
       subordinates expire.

       This slapd.conf(5) directive adds the dds overlay to the current

       overlay dds

       The database must have a rootdn specified, otherwise, the dds overlay
       will not be able to delete expired objects. The dds overlay may be used
       with any backend that implements the add, modify, search, and delete
       operations.  Since its use may result in many internal entry lookups,
       adds and deletes, it should be best used in conjunction with backends
       that have reasonably good write performances.

       The config directives that are specific to the dds overlay are prefixed
       by dds-, to avoid potential conflicts with directives specific to the
       underlying database or to other stacked overlays.

       dds-max-ttl <ttl>
              Specifies the max TTL value.  This is also the default TTL newly
              created dynamic objects receive, unless dds-default-ttl is set.
              When the client with a refresh extended operation requests a TTL
              higher than it, sizeLimitExceeded is returned.  This value must
              be between 86400 (1 day, the default) and 31557600 (1 year plus
              6 hours, as per RFC 2589).

       dds-min-ttl <ttl>
              Specifies the min TTL value; clients requesting a lower TTL by
              means of the refresh extended operation actually obtain this
              value as CRP.  If set to 0 (the default), no lower limit is set.

       dds-default-ttl <ttl>
              Specifies the default TTL value that newly created dynamic
              objects get.  If set to 0 (the default), the dds-max-ttl is

       dds-interval <ttl>
              Specifies the interval between expiration checks; defaults to 1

       dds-tolerance <ttl>
              Specifies an extra time that is added to the timer that actually
              wakes up the thread that will delete an expired dynamic object.
              So the nominal lifetime of the entry is that specified in the
              entryTtl attribute, but its lifetime will actually be entryTtl +
              tolerance.  Note that there is no guarantee that the lifetime of
              a dynamic object will be exactly the requested TTL; due to
              implementation details, it may be longer, which is allowed by
              RFC 2589.  By default, tolerance is 0.

       dds-max-dynamicObjects <num>
              Specifies the maximum number of dynamic objects that can
              simultaneously exist within a naming context.  This allows to
              limit the amount of resources (mostly in terms of run-queue
              size) that are used by dynamic objects.  By default, no limit is

       dds-state {TRUE|false}
              Specifies if the Dynamic Directory Services feature is enabled
              or not.  By default it is; however, a proxy does not need to
              keep track of dynamic objects itself, it only needs to inform
              the frontend that support for dynamic objects is available.

       The dds overlay restricts the refresh operation by requiring manage
       access to the entryTtl attribute (see slapd.access(5) for details about
       the manage access privilege).  Since the entryTtl is an operational,
       NO-USER-MODIFICATION attribute, no direct write access to it is
       possible.  So the dds overlay turns refresh extended operation into an
       internal modification to the value of the entryTtl attribute with the
       relax control set.

       RFC 2589 recommends that anonymous clients should not be allowed to
       refresh a dynamic object.  This can be implemented by appropriately
       crafting access control to obtain the desired effect.

       Example: restrict refresh to authenticated clients

              access to attrs=entryTtl
                   by users manage
                   by * read

       Example: restrict refresh to the creator of the dynamic object

              access to attrs=entryTtl
                   by dnattr=creatorsName manage
                   by * read

       Another suggested usage of dynamic objects is to implement dynamic
       meetings; in this case, all the participants to the meeting are allowed
       to refresh the meeting object, but only the creator can delete it
       (otherwise it will be deleted when the TTL expires)

       Example: assuming participant is a valid DN-valued attribute, allow
       users to start a meeting and to join it; restrict refresh to the
       participants; restrict delete to the creator

              access to dn.base="cn=Meetings"
                   by users write

              access to dn.onelevel="cn=Meetings"
                   by dnattr=creatorsName write
                   by * read

              access to dn.onelevel="cn=Meetings"
                   by dnattr=creatorsName write
                   by users selfwrite
                   by * read

              access to dn.onelevel="cn=Meetings"
                   by dnattr=participant manage
                   by * read

       This implementation of RFC 2589 provides a restricted interpretation of
       how dynamic objects replicate.  Only the master takes care of handling
       dynamic object expiration, while replicas simply see the dynamic object
       as a plain object.

       When replicating these objects, one needs to explicitly exclude the
       dynamicObject class and the entryTtl attribute.  This implementation of
       RFC 2589 introduces a new operational attribute, entryExpireTimestamp,
       that contains the expiration timestamp.  This must be excluded from
       replication as well.

       The quick and dirty solution is to set schemacheck=off in the syncrepl
       configuration and, optionally, exclude the operational attributes from
       replication, using

              syncrepl ...

       In any case the overlay must be either statically built in or run-time
       loaded by the consumer, so that it is aware of the entryExpireTimestamp
       operational attribute; however, it must not be configured in the shadow
       database.  Currently, there is no means to remove the dynamicObject
       class from the entry; this may be seen as a feature, since it allows to
       see the dynamic properties of the object.

              default slapd configuration file

       slapd.conf(5), slapd-config(5), slapd(8).

       Implemented by Pierangelo Masarati.

OpenLDAP 2.4.40                   2014/09/20                      SLAPO-DDS(5)