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-return-error TRUE
115 > updateref "ldap://ldapmaster.example.com/"
117 The {{B:chain-tls}} statement enables TLS from the slave to the ldap master.
118 The DITs are exactly the same between these machines, therefore whatever user
119 bound to the slave will also exist on the master. If that DN does not have
120 update privileges on the master, nothing will happen.
122 You will need to restart the slave after these changes. Then, if you are using
123 {{loglevel 256}}, you can monitor an {{ldapmodify}} on the slave and the master.
125 Now start an {{ldapmodify}} on the slave and watch the logs. You should expect
128 > 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)
129 > Sep 6 09:27:25 slave1 slapd[29274]: conn=11 op=0 STARTTLS
130 > Sep 6 09:27:25 slave1 slapd[29274]: conn=11 op=0 RESULT oid= err=0 text=
131 > Sep 6 09:27:25 slave1 slapd[29274]: conn=11 fd=31 TLS established tls_ssf=256 ssf=256
132 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=1 BIND dn="uid=user1,ou=people,dc=example,dc=com" method=128
133 > 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
134 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=1 RESULT tag=97 err=0 text=
135 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=2 MOD dn="uid=user1,ou=People,dc=example,dc=com"
136 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=2 MOD attr=mail
137 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=2 RESULT tag=103 err=0 text=
138 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=3 UNBIND
139 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 fd=31 closed
140 > Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: LDAP_RES_SEARCH_ENTRY(LDAP_SYNC_MODIFY)
141 > Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: be_search (0)
142 > Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: uid=user1,ou=People,dc=example,dc=com
143 > Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: be_modify (0)
145 And on the master you will see this:
147 > Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 PROXYAUTHZ dn="uid=user1,ou=people,dc=example,dc=com"
148 > Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 MOD dn="uid=user1,ou=People,dc=example,dc=com"
149 > Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 MOD attr=mail
150 > Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 RESULT tag=103 err=0 text=
152 Note: You can clearly see the PROXYAUTHZ line on the master, indicating the
153 proper identity assertion for the update on the master. Also note the slave
154 immediately receiving the Syncrepl update from the master.
162 This overlay enforces a regular expression constraint on all values
163 of specified attributes. It is used to enforce a more rigorous
164 syntax when the underlying attribute syntax is too general.
167 H3: Constraint Configuration
170 H2: Dynamic Directory Services
175 This overlay supports dynamic objects, which have a limited life after
176 which they expire and are automatically deleted.
179 H3: Dynamic Directory Service Configuration
187 This overlay extends the Compare operation to detect
188 members of a dynamic group. This overlay is now deprecated
189 as all of its functions are available using the
190 {{SECT:Dynamic Lists}} overlay.
193 H3: Dynamic Group Configuration
201 This overlay allows expansion of dynamic groups and more.
204 H3: Dynamic List Configuration
207 H2: Reverse Group Membership Maintenance
211 In some scenarios, it may be desirable for a client to be able to determine
212 which groups an entry is a member of, without performing an additional search.
213 Examples of this are applications using the {{TERM:DIT}} for access control
214 based on group authorization.
216 The {{B:memberof}} overlay updates an attribute (by default {{B:memberOf}}) whenever
217 changes occur to the membership attribute (by default {{B:member}}) of entries of the
218 objectclass (by default {{B:groupOfNames}}) configured to trigger updates.
220 Thus, it provides maintenance of the list of groups an entry is a member of,
221 when usual maintenance of groups is done by modifying the members on the group
224 H3: Member Of Configuration
226 The typical use of this overlay requires just enabling the overlay for a
227 specific database. For example, with the following minimal slapd.conf:
229 > include /usr/share/openldap/schema/core.schema
230 > include /usr/share/openldap/schema/cosine.schema
231 > modulepath /usr/lib/openldap
232 > moduleload memberof.la
233 > authz-regexp "gidNumber=0\\\+uidNumber=0,cn=peercred,cn=external,cn=auth"
234 > "cn=Manager,dc=example,dc=com"
236 > suffix "dc=example,dc=com"
237 > rootdn "cn=Manager,dc=example,dc=com"
239 > directory /var/lib/ldap2.4
241 > index objectClass eq
246 adding the following ldif:
249 > dn: dc=example,dc=com
250 > objectclass: domain
253 > dn: ou=Group,dc=example,dc=com
254 > objectclass: organizationalUnit
257 > dn: ou=People,dc=example,dc=com
258 > objectclass: organizationalUnit
261 > dn: uid=test1,ou=People,dc=example,dc=com
262 > objectclass: account
265 > dn: cn=testgroup,ou=Group,dc=example,dc=com
266 > objectclass: groupOfNames
268 > member: uid=test1,ou=People,dc=example,dc=com
270 Results in the following output from a search on the test1 user:
272 > # ldapsearch -LL -Y EXTERNAL -H ldapi:/// "(uid=test1)" -b dc=example,dc=com memberOf
273 > SASL/EXTERNAL authentication started
274 > SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
278 > dn: uid=test1,ou=People,dc=example,dc=com
279 > memberOf: cn=testgroup,ou=Group,dc=example,dc=com
281 Note that the {{B:memberOf}} attribute is an operational attribute, so it must be
282 requested explicitly.
285 H2: The Proxy Cache Engine
287 {{TERM:LDAP}} servers typically hold one or more subtrees of a
288 {{TERM:DIT}}. Replica (or shadow) servers hold shadow copies of
289 entries held by one or more master servers. Changes are propagated
290 from the master server to replica (slave) servers using LDAP Sync
291 replication. An LDAP cache is a special type of replica which holds
292 entries corresponding to search filters instead of subtrees.
296 The proxy cache extension of slapd is designed to improve the
297 responsiveness of the ldap and meta backends. It handles a search
299 by first determining whether it is contained in any cached search
300 filter. Contained requests are answered from the proxy cache's local
301 database. Other requests are passed on to the underlying ldap or
302 meta backend and processed as usual.
304 E.g. {{EX:(shoesize>=9)}} is contained in {{EX:(shoesize>=8)}} and
305 {{EX:(sn=Richardson)}} is contained in {{EX:(sn=Richards*)}}
307 Correct matching rules and syntaxes are used while comparing
308 assertions for query containment. To simplify the query containment
309 problem, a list of cacheable "templates" (defined below) is specified
310 at configuration time. A query is cached or answered only if it
311 belongs to one of these templates. The entries corresponding to
312 cached queries are stored in the proxy cache local database while
313 its associated meta information (filter, scope, base, attributes)
314 is stored in main memory.
316 A template is a prototype for generating LDAP search requests.
317 Templates are described by a prototype search filter and a list of
318 attributes which are required in queries generated from the template.
319 The representation for prototype filter is similar to {{REF:RFC4515}},
320 except that the assertion values are missing. Examples of prototype
321 filters are: (sn=),(&(sn=)(givenname=)) which are instantiated by
322 search filters (sn=Doe) and (&(sn=Doe)(givenname=John)) respectively.
324 The cache replacement policy removes the least recently used (LRU)
325 query and entries belonging to only that query. Queries are allowed
326 a maximum time to live (TTL) in the cache thus providing weak
327 consistency. A background task periodically checks the cache for
328 expired queries and removes them.
330 The Proxy Cache paper
331 ({{URL:http://www.openldap.org/pub/kapurva/proxycaching.pdf}}) provides
332 design and implementation details.
335 H3: Proxy Cache Configuration
337 The cache configuration specific directives described below must
338 appear after a {{EX:overlay proxycache}} directive within a
339 {{EX:"database meta"}} or {{EX:database ldap}} section of
340 the server's {{slapd.conf}}(5) file.
342 H4: Setting cache parameters
344 > proxyCache <DB> <maxentries> <nattrsets> <entrylimit> <period>
346 This directive enables proxy caching and sets general cache
347 parameters. The <DB> parameter specifies which underlying database
348 is to be used to hold cached entries. It should be set to
349 {{EX:bdb}} or {{EX:hdb}}. The <maxentries> parameter specifies the
350 total number of entries which may be held in the cache. The
351 <nattrsets> parameter specifies the total number of attribute sets
352 (as specified by the {{EX:proxyAttrSet}} directive) that may be
353 defined. The <entrylimit> parameter specifies the maximum number of
354 entries in a cacheable query. The <period> specifies the consistency
355 check period (in seconds). In each period, queries with expired
358 H4: Defining attribute sets
360 > proxyAttrset <index> <attrs...>
362 Used to associate a set of attributes to an index. Each attribute
363 set is associated with an index number from 0 to <numattrsets>-1.
364 These indices are used by the proxyTemplate directive to define
367 H4: Specifying cacheable templates
369 > proxyTemplate <prototype_string> <attrset_index> <TTL>
371 Specifies a cacheable template and the "time to live" (in sec) <TTL>
372 for queries belonging to the template. A template is described by
373 its prototype filter string and set of required attributes identified
379 An example {{slapd.conf}}(5) database section for a caching server
380 which proxies for the {{EX:"dc=example,dc=com"}} subtree held
381 at server {{EX:ldap.example.com}}.
384 > suffix "dc=example,dc=com"
385 > rootdn "dc=example,dc=com"
386 > uri ldap://ldap.example.com/dc=example%2cdc=com
388 > proxycache bdb 100000 1 1000 100
389 > proxyAttrset 0 mail postaladdress telephonenumber
390 > proxyTemplate (sn=) 0 3600
391 > proxyTemplate (&(sn=)(givenName=)) 0 3600
392 > proxyTemplate (&(departmentNumber=)(secretary=*)) 0 3600
395 > directory ./testrun/db.2.a
396 > index objectClass eq
397 > index cn,sn,uid,mail pres,eq,sub
400 H5: Cacheable Queries
402 A LDAP search query is cacheable when its filter matches one of the
403 templates as defined in the "proxyTemplate" statements and when it references
404 only the attributes specified in the corresponding attribute set.
405 In the example above the attribute set number 0 defines that only the
406 attributes: {{EX:mail postaladdress telephonenumber}} are cached for the following
411 > Filter: (&(sn=Richard*)(givenName=jack))
412 > Attrs: mail telephoneNumber
414 is cacheable, because it matches the template {{EX:(&(sn=)(givenName=))}} and its
415 attributes are contained in proxyAttrset 0.
417 > Filter: (&(sn=Richard*)(telephoneNumber))
420 is not cacheable, because the filter does not match the template,
421 nor is the attribute givenName stored in the cache
423 > Filter: (|(sn=Richard*)(givenName=jack))
424 > Attrs: mail telephoneNumber
426 is not cacheable, because the filter does not match the template ( logical
427 OR "|" condition instead of logical AND "&" )
430 H2: Password Policies
435 This overlay provides a variety of password control mechanisms,
436 e.g. password aging, password reuse and duplication control, mandatory
437 password resets, etc.
440 H3: Password Policy Configuration
443 H2: Referential Integrity
448 This overlay can be used with a backend database such as slapd-bdb (5)
449 to maintain the cohesiveness of a schema which utilizes reference
453 H3: Referential Integrity Configuration
461 This overlay is useful to test the behavior of clients when
462 server-generated erroneous and/or unusual responses occur.
465 H3: Return Code Configuration
473 It performs basic DN/data rewrite and
474 objectClass/attributeType mapping.
477 H3: Rewrite/Remap Configuration
485 This overlay implements the provider-side support for syncrepl
486 replication, including persistent search functionality
489 H3: Sync Provider Configuration
492 H2: Translucent Proxy
497 This overlay can be used with a backend database such as slapd-bdb (5)
498 to create a "translucent proxy".
500 Content of entries retrieved from a remote LDAP server can be partially
501 overridden by the database.
504 H3: Translucent Proxy Configuration
507 H2: Attribute Uniqueness
512 This overlay can be used with a backend database such as slapd-bdb (5)
513 to enforce the uniqueness of some or all attributes within a subtree.
516 H3: Attribute Uniqueness Configuration
524 This overlay can be used to enforce a specific order for the values
525 of an attribute when it is returned in a search.
528 H3: Value Sorting Configuration
537 H3: Example Scenarios