2 # Copyright 2007 The OpenLDAP Foundation, All Rights Reserved.
3 # COPYING RESTRICTIONS APPLY, see COPYRIGHT.
7 Overlays are software components that provide hooks to functions analogous to
8 those provided by backends, which can be stacked on top of the backend calls
9 and as callbacks on top of backend responses to alter their behavior.
11 Overlays may be compiled statically into slapd, or when module support
12 is enabled, they may be dynamically loaded. Most of the overlays
13 are only allowed to be configured on individual databases, but some
14 may also be configured globally.
16 Essentially they represent a means to:
18 * customize the behavior of existing backends without changing the backend
19 code and without requiring one to write a new custom backend with
20 complete functionality
21 * write functionality of general usefulness that can be applied to
22 different backend types
24 Overlays are usually documented by separate specific man pages in section 5;
25 the naming convention is
27 > slapo-<overlay name>
29 Not all distributed overlays have a man page yet. Feel free to contribute one,
30 if you think you well understood the behavior of the component and the
31 implications of all the related configuration directives.
33 Official overlays are located in
35 > servers/slapd/overlays/
37 That directory also contains the file slapover.txt, which describes the
38 rationale of the overlay implementation, and may serve as guideline for the
39 development of custom overlays.
41 Contribware overlays are located in
43 > contrib/slapd-modules/<overlay name>/
45 along with other types of run-time loadable components; they are officially
46 distributed, but not maintained by the project.
48 They can be stacked on the frontend as well; this means that they can be
49 executed after a request is parsed and validated, but right before the
50 appropriate database is selected. The main purpose is to affect operations
51 regardless of the database they will be handled by, and, in some cases,
52 to influence the selection of the database by massaging the request DN.
54 All the current overlays in 2.4 are listed and described in detail in the
63 This overlay can record accesses to a given backend database on another
67 H3: Access Logging Configuration
72 This overlay records changes on a given backend database to an LDIF log
79 H3: Audit Logging Configuration
87 The chain overlay provides basic chaining capability to the underlying
90 What is chaining? It indicates the capability of a DSA to follow referrals on
91 behalf of the client, so that distributed systems are viewed as a single
92 virtual DSA by clients that are otherwise unable to "chase" (i.e. follow)
93 referrals by themselves.
95 The chain overlay is built on top of the ldap backend; it is compiled by
96 default when --enable-ldap.
99 H3: Chaining Configuration
101 In order to demonstrate how this overlay works, we shall discuss a typical
102 scenario which might be one master server and three Syncrepl slaves.
104 On each replica, add this near the top of the file (global), before any database
108 > chain-uri "ldap://ldapmaster.example.com"
109 > chain-idassert-bind bindmethod="simple"
110 > binddn="cn=Manager,dc=example,dc=com"
111 > credentials="<secret>"
114 > chain-idassert-authzFrom "*"
115 > chain-return-error TRUE
116 > updateref "ldap://ldapmaster.example.com/"
118 The {{B:chain-tls}} statement enables TLS from the slave to the ldap master.
119 The {{B:chain-idassert-authzFrom}} statement will assert the identity of whatever
120 bound dn on the slave is making the update request. The DITs are exactly the
121 same between these machines, therefore whatever user bound to the slave will
122 also exist on the master. If that DN does not have update privileges on the master,
125 You will need to restart the slave after these changes. Then, if you are using
126 {{loglevel 256}}, you can monitor an {{ldapmodify}} on the slave and the master.
128 Now start an {{ldapmodify}} on the slave and watch the logs. You should expect
131 > Sep 6 09:27:25 slave1 slapd[29274]: conn=11 fd=31 ACCEPT from IP=143.199.102.216:45181 (IP=143.199.102.216:389)
132 > Sep 6 09:27:25 slave1 slapd[29274]: conn=11 op=0 STARTTLS
133 > Sep 6 09:27:25 slave1 slapd[29274]: conn=11 op=0 RESULT oid= err=0 text=
134 > Sep 6 09:27:25 slave1 slapd[29274]: conn=11 fd=31 TLS established tls_ssf=256 ssf=256
135 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=1 BIND dn="uid=user1,ou=people,dc=example,dc=com" method=128
136 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=1 BIND dn="uid=user1,ou=People,dc=example,dc=com" mech=SIMPLE ssf=0
137 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=1 RESULT tag=97 err=0 text=
138 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=2 MOD dn="uid=user1,ou=People,dc=example,dc=com"
139 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=2 MOD attr=mail
140 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=2 RESULT tag=103 err=0 text=
141 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=3 UNBIND
142 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 fd=31 closed
143 > Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: LDAP_RES_SEARCH_ENTRY(LDAP_SYNC_MODIFY)
144 > Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: be_search (0)
145 > Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: uid=user1,ou=People,dc=example,dc=com
146 > Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: be_modify (0)
148 And on the master you will see this:
150 > Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 PROXYAUTHZ dn="uid=user1,ou=people,dc=example,dc=com"
151 > Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 MOD dn="uid=user1,ou=People,dc=example,dc=com"
152 > Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 MOD attr=mail
153 > Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 RESULT tag=103 err=0 text=
155 Note: You can clearly see the PROXYAUTHZ line on the master, indicating the
156 proper identity assertion for the update on the master. Also note the slave
157 immediately receiving the Syncrepl update from the master.
165 This overlay enforces a regular expression constraint on all values
166 of specified attributes. It is used to enforce a more rigorous
167 syntax when the underlying attribute syntax is too general.
170 H3: Constraint Configuration
173 H2: Dynamic Directory Services
178 This overlay supports dynamic objects, which have a limited life after
179 which they expire and are automatically deleted.
182 H3: Dynamic Directory Service Configuration
190 This overlay extends the Compare operation to detect
191 members of a dynamic group. This overlay is now deprecated
192 as all of its functions are available using the
193 {{SECT:Dynamic Lists}} overlay.
196 H3: Dynamic Group Configuration
204 This overlay allows expansion of dynamic groups and more.
207 H3: Dynamic List Configuration
210 H2: Reverse Group Membership Maintenance
213 H3: Member Of Configuration
216 H2: The Proxy Cache Engine
218 {{TERM:LDAP}} servers typically hold one or more subtrees of a
219 {{TERM:DIT}}. Replica (or shadow) servers hold shadow copies of
220 entries held by one or more master servers. Changes are propagated
221 from the master server to replica (slave) servers using LDAP Sync
222 replication. An LDAP cache is a special type of replica which holds
223 entries corresponding to search filters instead of subtrees.
227 The proxy cache extension of slapd is designed to improve the
228 responsiveness of the ldap and meta backends. It handles a search
230 by first determining whether it is contained in any cached search
231 filter. Contained requests are answered from the proxy cache's local
232 database. Other requests are passed on to the underlying ldap or
233 meta backend and processed as usual.
235 E.g. {{EX:(shoesize>=9)}} is contained in {{EX:(shoesize>=8)}} and
236 {{EX:(sn=Richardson)}} is contained in {{EX:(sn=Richards*)}}
238 Correct matching rules and syntaxes are used while comparing
239 assertions for query containment. To simplify the query containment
240 problem, a list of cacheable "templates" (defined below) is specified
241 at configuration time. A query is cached or answered only if it
242 belongs to one of these templates. The entries corresponding to
243 cached queries are stored in the proxy cache local database while
244 its associated meta information (filter, scope, base, attributes)
245 is stored in main memory.
247 A template is a prototype for generating LDAP search requests.
248 Templates are described by a prototype search filter and a list of
249 attributes which are required in queries generated from the template.
250 The representation for prototype filter is similar to {{REF:RFC4515}},
251 except that the assertion values are missing. Examples of prototype
252 filters are: (sn=),(&(sn=)(givenname=)) which are instantiated by
253 search filters (sn=Doe) and (&(sn=Doe)(givenname=John)) respectively.
255 The cache replacement policy removes the least recently used (LRU)
256 query and entries belonging to only that query. Queries are allowed
257 a maximum time to live (TTL) in the cache thus providing weak
258 consistency. A background task periodically checks the cache for
259 expired queries and removes them.
261 The Proxy Cache paper
262 ({{URL:http://www.openldap.org/pub/kapurva/proxycaching.pdf}}) provides
263 design and implementation details.
266 H3: Proxy Cache Configuration
268 The cache configuration specific directives described below must
269 appear after a {{EX:overlay proxycache}} directive within a
270 {{EX:"database meta"}} or {{EX:database ldap}} section of
271 the server's {{slapd.conf}}(5) file.
273 H4: Setting cache parameters
275 > proxyCache <DB> <maxentries> <nattrsets> <entrylimit> <period>
277 This directive enables proxy caching and sets general cache
278 parameters. The <DB> parameter specifies which underlying database
279 is to be used to hold cached entries. It should be set to
280 {{EX:bdb}} or {{EX:hdb}}. The <maxentries> parameter specifies the
281 total number of entries which may be held in the cache. The
282 <nattrsets> parameter specifies the total number of attribute sets
283 (as specified by the {{EX:proxyAttrSet}} directive) that may be
284 defined. The <entrylimit> parameter specifies the maximum number of
285 entries in a cacheable query. The <period> specifies the consistency
286 check period (in seconds). In each period, queries with expired
289 H4: Defining attribute sets
291 > proxyAttrset <index> <attrs...>
293 Used to associate a set of attributes to an index. Each attribute
294 set is associated with an index number from 0 to <numattrsets>-1.
295 These indices are used by the proxyTemplate directive to define
298 H4: Specifying cacheable templates
300 > proxyTemplate <prototype_string> <attrset_index> <TTL>
302 Specifies a cacheable template and the "time to live" (in sec) <TTL>
303 for queries belonging to the template. A template is described by
304 its prototype filter string and set of required attributes identified
310 An example {{slapd.conf}}(5) database section for a caching server
311 which proxies for the {{EX:"dc=example,dc=com"}} subtree held
312 at server {{EX:ldap.example.com}}.
315 > suffix "dc=example,dc=com"
316 > rootdn "dc=example,dc=com"
317 > uri ldap://ldap.example.com/dc=example%2cdc=com
319 > proxycache bdb 100000 1 1000 100
320 > proxyAttrset 0 mail postaladdress telephonenumber
321 > proxyTemplate (sn=) 0 3600
322 > proxyTemplate (&(sn=)(givenName=)) 0 3600
323 > proxyTemplate (&(departmentNumber=)(secretary=*)) 0 3600
326 > directory ./testrun/db.2.a
327 > index objectClass eq
328 > index cn,sn,uid,mail pres,eq,sub
331 H5: Cacheable Queries
333 A LDAP search query is cacheable when its filter matches one of the
334 templates as defined in the "proxyTemplate" statements and when it references
335 only the attributes specified in the corresponding attribute set.
336 In the example above the attribute set number 0 defines that only the
337 attributes: {{EX:mail postaladdress telephonenumber}} are cached for the following
342 > Filter: (&(sn=Richard*)(givenName=jack))
343 > Attrs: mail telephoneNumber
345 is cacheable, because it matches the template {{EX:(&(sn=)(givenName=))}} and its
346 attributes are contained in proxyAttrset 0.
348 > Filter: (&(sn=Richard*)(telephoneNumber))
351 is not cacheable, because the filter does not match the template,
352 nor is the attribute givenName stored in the cache
354 > Filter: (|(sn=Richard*)(givenName=jack))
355 > Attrs: mail telephoneNumber
357 is not cacheable, because the filter does not match the template ( logical
358 OR "|" condition instead of logical AND "&" )
361 H2: Password Policies
366 This overlay provides a variety of password control mechanisms,
367 e.g. password aging, password reuse and duplication control, mandatory
368 password resets, etc.
371 H3: Password Policy Configuration
374 H2: Referential Integrity
379 This overlay can be used with a backend database such as slapd-bdb (5)
380 to maintain the cohesiveness of a schema which utilizes reference
384 H3: Referential Integrity Configuration
392 This overlay is useful to test the behavior of clients when
393 server-generated erroneous and/or unusual responses occur.
396 H3: Return Code Configuration
404 It performs basic DN/data rewrite and
405 objectClass/attributeType mapping.
408 H3: Rewrite/Remap Configuration
416 This overlay implements the provider-side support for syncrepl
417 replication, including persistent search functionality
420 H3: Sync Provider Configuration
423 H2: Translucent Proxy
428 This overlay can be used with a backend database such as slapd-bdb (5)
429 to create a "translucent proxy".
431 Content of entries retrieved from a remote LDAP server can be partially
432 overridden by the database.
435 H3: Translucent Proxy Configuration
438 H2: Attribute Uniqueness
443 This overlay can be used with a backend database such as slapd-bdb (5)
444 to enforce the uniqueness of some or all attributes within a subtree.
447 H3: Attribute Uniqueness Configuration
455 This overlay can be used to enforce a specific order for the values
456 of an attribute when it is returned in a search.
459 H3: Value Sorting Configuration
468 H3: Example Scenarios