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
116 Add this below your {{syncrepl}} statement:
118 > updateref "ldap://ldapmaster.example.com/"
120 The {{B:chain-tls}} statement enables TLS from the slave to the ldap master.
121 The DITs are exactly the same between these machines, therefore whatever user
122 bound to the slave will also exist on the master. If that DN does not have
123 update privileges on the master, nothing will happen.
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.
159 H3: Handling Chaining Errors
161 By default, if chaining fails, the original referral is returned to the client
162 under the assumption that the client might want to try and follow the referral.
164 With the following directive however, if the chaining fails at the provider
165 side, the actual error is returned to the client.
167 > chain-return-error TRUE
175 This overlay enforces a regular expression constraint on all values
176 of specified attributes. It is used to enforce a more rigorous
177 syntax when the underlying attribute syntax is too general.
180 H3: Constraint Configuration
183 H2: Dynamic Directory Services
188 This overlay supports dynamic objects, which have a limited life after
189 which they expire and are automatically deleted.
192 H3: Dynamic Directory Service Configuration
200 This overlay extends the Compare operation to detect
201 members of a dynamic group. This overlay is now deprecated
202 as all of its functions are available using the
203 {{SECT:Dynamic Lists}} overlay.
206 H3: Dynamic Group Configuration
214 This overlay allows expansion of dynamic groups and more.
217 H3: Dynamic List Configuration
220 H2: Reverse Group Membership Maintenance
224 In some scenarios, it may be desirable for a client to be able to determine
225 which groups an entry is a member of, without performing an additional search.
226 Examples of this are applications using the {{TERM:DIT}} for access control
227 based on group authorization.
229 The {{B:memberof}} overlay updates an attribute (by default {{B:memberOf}}) whenever
230 changes occur to the membership attribute (by default {{B:member}}) of entries of the
231 objectclass (by default {{B:groupOfNames}}) configured to trigger updates.
233 Thus, it provides maintenance of the list of groups an entry is a member of,
234 when usual maintenance of groups is done by modifying the members on the group
237 H3: Member Of Configuration
239 The typical use of this overlay requires just enabling the overlay for a
240 specific database. For example, with the following minimal slapd.conf:
242 > include /usr/share/openldap/schema/core.schema
243 > include /usr/share/openldap/schema/cosine.schema
244 > modulepath /usr/lib/openldap
245 > moduleload memberof.la
246 > authz-regexp "gidNumber=0\\\+uidNumber=0,cn=peercred,cn=external,cn=auth"
247 > "cn=Manager,dc=example,dc=com"
249 > suffix "dc=example,dc=com"
250 > rootdn "cn=Manager,dc=example,dc=com"
252 > directory /var/lib/ldap2.4
254 > index objectClass eq
259 adding the following ldif:
262 > dn: dc=example,dc=com
263 > objectclass: domain
266 > dn: ou=Group,dc=example,dc=com
267 > objectclass: organizationalUnit
270 > dn: ou=People,dc=example,dc=com
271 > objectclass: organizationalUnit
274 > dn: uid=test1,ou=People,dc=example,dc=com
275 > objectclass: account
278 > dn: cn=testgroup,ou=Group,dc=example,dc=com
279 > objectclass: groupOfNames
281 > member: uid=test1,ou=People,dc=example,dc=com
283 Results in the following output from a search on the test1 user:
285 > # ldapsearch -LL -Y EXTERNAL -H ldapi:/// "(uid=test1)" -b dc=example,dc=com memberOf
286 > SASL/EXTERNAL authentication started
287 > SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
291 > dn: uid=test1,ou=People,dc=example,dc=com
292 > memberOf: cn=testgroup,ou=Group,dc=example,dc=com
294 Note that the {{B:memberOf}} attribute is an operational attribute, so it must be
295 requested explicitly.
298 H2: The Proxy Cache Engine
300 {{TERM:LDAP}} servers typically hold one or more subtrees of a
301 {{TERM:DIT}}. Replica (or shadow) servers hold shadow copies of
302 entries held by one or more master servers. Changes are propagated
303 from the master server to replica (slave) servers using LDAP Sync
304 replication. An LDAP cache is a special type of replica which holds
305 entries corresponding to search filters instead of subtrees.
309 The proxy cache extension of slapd is designed to improve the
310 responsiveness of the ldap and meta backends. It handles a search
312 by first determining whether it is contained in any cached search
313 filter. Contained requests are answered from the proxy cache's local
314 database. Other requests are passed on to the underlying ldap or
315 meta backend and processed as usual.
317 E.g. {{EX:(shoesize>=9)}} is contained in {{EX:(shoesize>=8)}} and
318 {{EX:(sn=Richardson)}} is contained in {{EX:(sn=Richards*)}}
320 Correct matching rules and syntaxes are used while comparing
321 assertions for query containment. To simplify the query containment
322 problem, a list of cacheable "templates" (defined below) is specified
323 at configuration time. A query is cached or answered only if it
324 belongs to one of these templates. The entries corresponding to
325 cached queries are stored in the proxy cache local database while
326 its associated meta information (filter, scope, base, attributes)
327 is stored in main memory.
329 A template is a prototype for generating LDAP search requests.
330 Templates are described by a prototype search filter and a list of
331 attributes which are required in queries generated from the template.
332 The representation for prototype filter is similar to {{REF:RFC4515}},
333 except that the assertion values are missing. Examples of prototype
334 filters are: (sn=),(&(sn=)(givenname=)) which are instantiated by
335 search filters (sn=Doe) and (&(sn=Doe)(givenname=John)) respectively.
337 The cache replacement policy removes the least recently used (LRU)
338 query and entries belonging to only that query. Queries are allowed
339 a maximum time to live (TTL) in the cache thus providing weak
340 consistency. A background task periodically checks the cache for
341 expired queries and removes them.
343 The Proxy Cache paper
344 ({{URL:http://www.openldap.org/pub/kapurva/proxycaching.pdf}}) provides
345 design and implementation details.
348 H3: Proxy Cache Configuration
350 The cache configuration specific directives described below must
351 appear after a {{EX:overlay proxycache}} directive within a
352 {{EX:"database meta"}} or {{EX:database ldap}} section of
353 the server's {{slapd.conf}}(5) file.
355 H4: Setting cache parameters
357 > proxyCache <DB> <maxentries> <nattrsets> <entrylimit> <period>
359 This directive enables proxy caching and sets general cache
360 parameters. The <DB> parameter specifies which underlying database
361 is to be used to hold cached entries. It should be set to
362 {{EX:bdb}} or {{EX:hdb}}. The <maxentries> parameter specifies the
363 total number of entries which may be held in the cache. The
364 <nattrsets> parameter specifies the total number of attribute sets
365 (as specified by the {{EX:proxyAttrSet}} directive) that may be
366 defined. The <entrylimit> parameter specifies the maximum number of
367 entries in a cacheable query. The <period> specifies the consistency
368 check period (in seconds). In each period, queries with expired
371 H4: Defining attribute sets
373 > proxyAttrset <index> <attrs...>
375 Used to associate a set of attributes to an index. Each attribute
376 set is associated with an index number from 0 to <numattrsets>-1.
377 These indices are used by the proxyTemplate directive to define
380 H4: Specifying cacheable templates
382 > proxyTemplate <prototype_string> <attrset_index> <TTL>
384 Specifies a cacheable template and the "time to live" (in sec) <TTL>
385 for queries belonging to the template. A template is described by
386 its prototype filter string and set of required attributes identified
392 An example {{slapd.conf}}(5) database section for a caching server
393 which proxies for the {{EX:"dc=example,dc=com"}} subtree held
394 at server {{EX:ldap.example.com}}.
397 > suffix "dc=example,dc=com"
398 > rootdn "dc=example,dc=com"
399 > uri ldap://ldap.example.com/dc=example%2cdc=com
401 > proxycache bdb 100000 1 1000 100
402 > proxyAttrset 0 mail postaladdress telephonenumber
403 > proxyTemplate (sn=) 0 3600
404 > proxyTemplate (&(sn=)(givenName=)) 0 3600
405 > proxyTemplate (&(departmentNumber=)(secretary=*)) 0 3600
408 > directory ./testrun/db.2.a
409 > index objectClass eq
410 > index cn,sn,uid,mail pres,eq,sub
413 H5: Cacheable Queries
415 A LDAP search query is cacheable when its filter matches one of the
416 templates as defined in the "proxyTemplate" statements and when it references
417 only the attributes specified in the corresponding attribute set.
418 In the example above the attribute set number 0 defines that only the
419 attributes: {{EX:mail postaladdress telephonenumber}} are cached for the following
424 > Filter: (&(sn=Richard*)(givenName=jack))
425 > Attrs: mail telephoneNumber
427 is cacheable, because it matches the template {{EX:(&(sn=)(givenName=))}} and its
428 attributes are contained in proxyAttrset 0.
430 > Filter: (&(sn=Richard*)(telephoneNumber))
433 is not cacheable, because the filter does not match the template,
434 nor is the attribute givenName stored in the cache
436 > Filter: (|(sn=Richard*)(givenName=jack))
437 > Attrs: mail telephoneNumber
439 is not cacheable, because the filter does not match the template ( logical
440 OR "|" condition instead of logical AND "&" )
443 H2: Password Policies
448 This overlay provides a variety of password control mechanisms,
449 e.g. password aging, password reuse and duplication control, mandatory
450 password resets, etc.
453 H3: Password Policy Configuration
456 H2: Referential Integrity
461 This overlay can be used with a backend database such as slapd-bdb (5)
462 to maintain the cohesiveness of a schema which utilizes reference
466 H3: Referential Integrity Configuration
474 This overlay is useful to test the behavior of clients when
475 server-generated erroneous and/or unusual responses occur.
478 H3: Return Code Configuration
486 It performs basic DN/data rewrite and
487 objectClass/attributeType mapping.
490 H3: Rewrite/Remap Configuration
498 This overlay implements the provider-side support for syncrepl
499 replication, including persistent search functionality
502 H3: Sync Provider Configuration
505 H2: Translucent Proxy
510 This overlay can be used with a backend database such as slapd-bdb (5)
511 to create a "translucent proxy".
513 Content of entries retrieved from a remote LDAP server can be partially
514 overridden by the database.
517 H3: Translucent Proxy Configuration
520 H2: Attribute Uniqueness
525 This overlay can be used with a backend database such as slapd-bdb (5)
526 to enforce the uniqueness of some or all attributes within a subtree.
529 H3: Attribute Uniqueness Configuration
537 This overlay can be used to enforce a specific order for the values
538 of an attribute when it is returned in a search.
541 H3: Value Sorting Configuration
550 H3: Example Scenarios