1SLAPO-DDS(5) File Formats Manual SLAPO-DDS(5)
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6 slapo-dds - Dynamic Directory Services overlay to slapd
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9 /etc/openldap/slapd.conf
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12 The dds overlay to slapd(8) implements dynamic objects as per RFC 2589.
13 The name dds stands for Dynamic Directory Services. It allows one to
14 define dynamic objects, characterized by the dynamicObject objectClass.
15 Dynamic objects have a limited lifetime, determined by a time-to-live
17 (TTL) that can be refreshed by means of a specific refresh extended
18 operation. This operation allows one to set the Client Refresh Period
19 (CRP), namely the period between refreshes that is required to preserve
20 the dynamic object from expiration. The expiration time is computed by
21 adding the requested TTL to the current time. When dynamic objects
22 reach the end of their lifetime without being further refreshed, they
23 are automatically deleted. There is no guarantee of immediate dele‐
24 tion, so clients should not count on it.
25 Dynamic objects can have subordinates, provided these also are dynamic
27 objects. RFC 2589 does not specify what the behavior of a dynamic
28 directory service should be when a dynamic object with (dynamic) subor‐
29 dinates expires. In this implementation, the lifetime of dynamic
30 objects with subordinates is prolonged until all the dynamic subordi‐
31 nates expire.
32 This slapd.conf(5) directive adds the dds overlay to the current data‐
35 base:
36 overlay dds
39 The database must have a rootdn specified, otherwise, the dds overlay
42 will not be able to delete expired objects. The dds overlay may be used
43 with any backend that implements the add, modify, search, and delete
44 operations. Since its use may result in many internal entry lookups,
45 adds and deletes, it should be best used in conjunction with backends
46 that have reasonably good write performances.
47 The config directives that are specific to the dds overlay are prefixed
50 by dds-, to avoid potential conflicts with directives specific to the
51 underlying database or to other stacked overlays.
52 dds-max-ttl <ttl>
55 Specifies the max TTL value. This is also the default TTL newly
56 created dynamic objects receive, unless dds-default-ttl is set.
57 When the client with a refresh extended operation requests a TTL
58 higher than it, sizeLimitExceeded is returned. This value must
59 be between 86400 (1 day, the default) and 31557600 (1 year plus
60 6 hours, as per RFC 2589).
61 dds-min-ttl <ttl>
64 Specifies the min TTL value; clients requesting a lower TTL by
65 means of the refresh extended operation actually obtain this
66 value as CRP. If set to 0 (the default), no lower limit is set.
67 dds-default-ttl <ttl>
70 Specifies the default TTL value that newly created dynamic
71 objects get. If set to 0 (the default), the dds-max-ttl is
72 used.
73 dds-interval <ttl>
76 Specifies the interval between expiration checks; defaults to 1
77 hour.
78 dds-tolerance <ttl>
81 Specifies an extra time that is added to the timer that actually
82 wakes up the thread that will delete an expired dynamic object.
83 So the nominal lifetime of the entry is that specified in the
84 entryTtl attribute, but its lifetime will actually be entryTtl +
85 tolerance. Note that there is no guarantee that the lifetime of
86 a dynamic object will be exactly the requested TTL; due to
87 implementation details, it may be longer, which is allowed by
88 RFC 2589. By default, tolerance is 0.
89 dds-max-dynamicObjects <num>
92 Specifies the maximum number of dynamic objects that can simul‐
93 taneously exist within a naming context. This allows one to
94 limit the amount of resources (mostly in terms of run-queue
95 size) that are used by dynamic objects. By default, no limit is
96 set.
97 dds-state {TRUE|false}
100 Specifies if the Dynamic Directory Services feature is enabled
101 or not. By default it is; however, a proxy does not need to
102 keep track of dynamic objects itself, it only needs to inform
103 the frontend that support for dynamic objects is available.
104
107 The dds overlay restricts the refresh operation by requiring manage
108 access to the entryTtl attribute (see slapd.access(5) for details about
109 the manage access privilege). Since the entryTtl is an operational,
110 NO-USER-MODIFICATION attribute, no direct write access to it is possi‐
111 ble. So the dds overlay turns refresh extended operation into an
112 internal modification to the value of the entryTtl attribute with the
113 relax control set.
114 RFC 2589 recommends that anonymous clients should not be allowed to
116 refresh a dynamic object. This can be implemented by appropriately
117 crafting access control to obtain the desired effect.
118 Example: restrict refresh to authenticated clients
120 access to attrs=entryTtl
122 by users manage
123 by * read
124 Example: restrict refresh to the creator of the dynamic object
126 access to attrs=entryTtl
128 by dnattr=creatorsName manage
129 by * read
130 Another suggested usage of dynamic objects is to implement dynamic
132 meetings; in this case, all the participants to the meeting are allowed
133 to refresh the meeting object, but only the creator can delete it (oth‐
134 erwise it will be deleted when the TTL expires)
135 Example: assuming participant is a valid DN-valued attribute, allow
137 users to start a meeting and to join it; restrict refresh to the par‐
138 ticipants; restrict delete to the creator
139 access to dn.base="cn=Meetings"
141 attrs=children
142 by users write
143 access to dn.onelevel="cn=Meetings"
145 attrs=entry
146 by dnattr=creatorsName write
147 by * read
148 access to dn.onelevel="cn=Meetings"
150 attrs=participant
151 by dnattr=creatorsName write
152 by users selfwrite
153 by * read
154 access to dn.onelevel="cn=Meetings"
156 attrs=entryTtl
157 by dnattr=participant manage
158 by * read
159
163 This implementation of RFC 2589 provides a restricted interpretation of
164 how dynamic objects replicate. Only the master takes care of handling
165 dynamic object expiration, while replicas simply see the dynamic object
166 as a plain object.
167 When replicating these objects, one needs to explicitly exclude the
169 dynamicObject class and the entryTtl attribute. This implementation of
170 RFC 2589 introduces a new operational attribute, entryExpireTimestamp,
171 that contains the expiration timestamp. This must be excluded from
172 replication as well.
173 The quick and dirty solution is to set schemacheck=off in the syncrepl
175 configuration and, optionally, exclude the operational attributes from
176 replication, using
177 syncrepl ...
179 exattrs=entryTtl,entryExpireTimestamp
180 In any case the overlay must be either statically built in or run-time
182 loaded by the consumer, so that it is aware of the entryExpireTimestamp
183 operational attribute; however, it must not be configured in the shadow
184 database. Currently, there is no means to remove the dynamicObject
185 class from the entry; this may be seen as a feature, since it allows
186 one to see the dynamic properties of the object.
187
190 /etc/openldap/slapd.conf
191 default slapd configuration file
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194 slapd.conf(5), slapd-config(5), slapd(8).
195
197 Implemented by Pierangelo Masarati.
198OpenLDAP 2.4.47 2018/12/19 SLAPO-DDS(5)