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 op‐
18 eration. 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 di‐
28 rectory service should be when a dynamic object with (dynamic) subordi‐
29 nates expires. In this implementation, the lifetime of dynamic objects
30 with subordinates is prolonged until all the dynamic subordinates ex‐
31 pire.
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 ob‐
71 jects get. If set to 0 (the default), the dds-max-ttl is used.
72 dds-interval <ttl>
75 Specifies the interval between expiration checks; defaults to 1
76 hour.
77 dds-tolerance <ttl>
80 Specifies an extra time that is added to the timer that actually
81 wakes up the thread that will delete an expired dynamic object.
82 So the nominal lifetime of the entry is that specified in the
83 entryTtl attribute, but its lifetime will actually be entryTtl +
84 tolerance. Note that there is no guarantee that the lifetime of
85 a dynamic object will be exactly the requested TTL; due to im‐
86 plementation details, it may be longer, which is allowed by RFC
87 2589. By default, tolerance is 0.
88 dds-max-dynamicObjects <num>
91 Specifies the maximum number of dynamic objects that can simul‐
92 taneously exist within a naming context. This allows one to
93 limit the amount of resources (mostly in terms of run-queue
94 size) that are used by dynamic objects. By default, no limit is
95 set.
96 dds-state {TRUE|false}
99 Specifies if the Dynamic Directory Services feature is enabled
100 or not. By default it is; however, a proxy does not need to
101 keep track of dynamic objects itself, it only needs to inform
102 the frontend that support for dynamic objects is available.
103
106 The dds overlay restricts the refresh operation by requiring manage ac‐
107 cess to the entryTtl attribute (see slapd.access(5) for details about
108 the manage access privilege). Since the entryTtl is an operational,
109 NO-USER-MODIFICATION attribute, no direct write access to it is possi‐
110 ble. So the dds overlay turns refresh extended operation into an in‐
111 ternal modification to the value of the entryTtl attribute with the re‐
112 lax control set.
113 RFC 2589 recommends that anonymous clients should not be allowed to re‐
115 fresh a dynamic object. This can be implemented by appropriately
116 crafting access control to obtain the desired effect.
117 Example: restrict refresh to authenticated clients
119 access to attrs=entryTtl
121 by users manage
122 by * read
123 Example: restrict refresh to the creator of the dynamic object
125 access to attrs=entryTtl
127 by dnattr=creatorsName manage
128 by * read
129 Another suggested usage of dynamic objects is to implement dynamic
131 meetings; in this case, all the participants to the meeting are allowed
132 to refresh the meeting object, but only the creator can delete it (oth‐
133 erwise it will be deleted when the TTL expires)
134 Example: assuming participant is a valid DN-valued attribute, allow
136 users to start a meeting and to join it; restrict refresh to the par‐
137 ticipants; restrict delete to the creator
138 access to dn.base="cn=Meetings"
140 attrs=children
141 by users write
142 access to dn.onelevel="cn=Meetings"
144 attrs=entry
145 by dnattr=creatorsName write
146 by * read
147 access to dn.onelevel="cn=Meetings"
149 attrs=participant
150 by dnattr=creatorsName write
151 by users selfwrite
152 by * read
153 access to dn.onelevel="cn=Meetings"
155 attrs=entryTtl
156 by dnattr=participant manage
157 by * read
158
162 This implementation of RFC 2589 provides a restricted interpretation of
163 how dynamic objects replicate. Only the provider takes care of han‐
164 dling dynamic object expiration, while consumers simply see the dynamic
165 object as a plain object.
166 When replicating these objects, one needs to explicitly exclude the dy‐
168 namicObject class and the entryTtl attribute. This implementation of
169 RFC 2589 introduces a new operational attribute, entryExpireTimestamp,
170 that contains the expiration timestamp. This must be excluded from
171 replication as well.
172 The quick and dirty solution is to set schemacheck=off in the syncrepl
174 configuration and, optionally, exclude the operational attributes from
175 replication, using
176 syncrepl ...
178 exattrs=entryTtl,entryExpireTimestamp
179 In any case the overlay must be either statically built in or run-time
181 loaded by the consumer, so that it is aware of the entryExpireTimestamp
182 operational attribute; however, it must not be configured in the shadow
183 database. Currently, there is no means to remove the dynamicObject
184 class from the entry; this may be seen as a feature, since it allows
185 one to see the dynamic properties of the object.
186
189 /etc/openldap/slapd.conf
190 default slapd configuration file
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193 slapd.conf(5), slapd-config(5), slapd(8).
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196 Implemented by Pierangelo Masarati.
197OpenLDAP 2.4.57 2021/01/18 SLAPO-DDS(5)