Provided by: slapd_2.5.13+dfsg-1ubuntu1_amd64 
NAME
slapo-dds - Dynamic Directory Services overlay to slapd
SYNOPSIS
/etc/ldap/slapd.conf
DESCRIPTION
The dds overlay to slapd(8) implements dynamic objects as per RFC 2589. The name dds
stands for Dynamic Directory Services. It allows one 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 one 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 database:
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 <time>
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 <time>
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 <time>
Specifies the default TTL value that newly created dynamic objects get. If set to
0 (the default), the dds-max-ttl is used.
dds-interval <time>
Specifies the interval between expiration checks; defaults to 1 hour.
dds-tolerance <time>
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 one to limit the amount of resources (mostly
in terms of run-queue size) that are used by dynamic objects. By default, no limit
is set.
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.
ACCESS CONTROL
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"
attrs=children
by users write
access to dn.onelevel="cn=Meetings"
attrs=entry
by dnattr=creatorsName write
by * read
access to dn.onelevel="cn=Meetings"
attrs=participant
by dnattr=creatorsName write
by users selfwrite
by * read
access to dn.onelevel="cn=Meetings"
attrs=entryTtl
by dnattr=participant manage
by * read
REPLICATION
This implementation of RFC 2589 provides a restricted interpretation of how dynamic
objects replicate. Only the provider takes care of handling dynamic object expiration,
while consumers 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 ...
exattrs=entryTtl,entryExpireTimestamp
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 one
to see the dynamic properties of the object.
FILES
/etc/ldap/slapd.conf
default slapd configuration file
SEE ALSO
slapd.conf(5), slapd-config(5), slapd(8).
AUTHOR
Implemented by Pierangelo Masarati.