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NAME | SYNOPSIS | DESCRIPTION | ACCESS CONTROL | REPLICATION | FILES | SEE ALSO | AUTHOR | COLOPHON |
SLAPO-DDS(5) File Formats Manual SLAPO-DDS(5)
slapo-dds - Dynamic Directory Services overlay to slapd
ETCDIR/slapd.conf
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 <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
used.
dds-interval <ttl>
Specifies the interval between expiration checks; defaults to
1 hour.
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 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.
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
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 ...
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.
ETCDIR/slapd.conf
default slapd configuration file
slapd.conf(5), slapd-config(5), slapd(8).
Implemented by Pierangelo Masarati.
This page is part of the OpenLDAP (an open source implementation of
the Lightweight Directory Access Protocol) project. Information
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⟨http://www.openldap.org/its/⟩. This page was obtained from the
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COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
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