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.
156 H3: Handling Chaining Errors
158 By default, if chaining fails, the original referral is returned to the client
159 under the assumption that the client might want to try and follow the referral.
161 With the following directive however, if the chaining fails at the provider
162 side, the actual error is returned to the client.
164 > chain-return-error TRUE
172 This overlay enforces a regular expression constraint on all values
173 of specified attributes. It is used to enforce a more rigorous
174 syntax when the underlying attribute syntax is too general.
177 H3: Constraint Configuration
180 H2: Dynamic Directory Services
185 This overlay supports dynamic objects, which have a limited life after
186 which they expire and are automatically deleted.
189 H3: Dynamic Directory Service Configuration
197 This overlay extends the Compare operation to detect
198 members of a dynamic group. This overlay is now deprecated
199 as all of its functions are available using the
200 {{SECT:Dynamic Lists}} overlay.
203 H3: Dynamic Group Configuration
211 This overlay allows expansion of dynamic groups and more.
214 H3: Dynamic List Configuration
217 H2: Reverse Group Membership Maintenance
221 In some scenarios, it may be desirable for a client to be able to determine
222 which groups an entry is a member of, without performing an additional search.
223 Examples of this are applications using the {{TERM:DIT}} for access control
224 based on group authorization.
226 The {{B:memberof}} overlay updates an attribute (by default {{B:memberOf}}) whenever
227 changes occur to the membership attribute (by default {{B:member}}) of entries of the
228 objectclass (by default {{B:groupOfNames}}) configured to trigger updates.
230 Thus, it provides maintenance of the list of groups an entry is a member of,
231 when usual maintenance of groups is done by modifying the members on the group
234 H3: Member Of Configuration
236 The typical use of this overlay requires just enabling the overlay for a
237 specific database. For example, with the following minimal slapd.conf:
239 > include /usr/share/openldap/schema/core.schema
240 > include /usr/share/openldap/schema/cosine.schema
241 > modulepath /usr/lib/openldap
242 > moduleload memberof.la
243 > authz-regexp "gidNumber=0\\\+uidNumber=0,cn=peercred,cn=external,cn=auth"
244 > "cn=Manager,dc=example,dc=com"
246 > suffix "dc=example,dc=com"
247 > rootdn "cn=Manager,dc=example,dc=com"
249 > directory /var/lib/ldap2.4
251 > index objectClass eq
256 adding the following ldif:
259 > dn: dc=example,dc=com
260 > objectclass: domain
263 > dn: ou=Group,dc=example,dc=com
264 > objectclass: organizationalUnit
267 > dn: ou=People,dc=example,dc=com
268 > objectclass: organizationalUnit
271 > dn: uid=test1,ou=People,dc=example,dc=com
272 > objectclass: account
275 > dn: cn=testgroup,ou=Group,dc=example,dc=com
276 > objectclass: groupOfNames
278 > member: uid=test1,ou=People,dc=example,dc=com
280 Results in the following output from a search on the test1 user:
282 > # ldapsearch -LL -Y EXTERNAL -H ldapi:/// "(uid=test1)" -b dc=example,dc=com memberOf
283 > SASL/EXTERNAL authentication started
284 > SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
288 > dn: uid=test1,ou=People,dc=example,dc=com
289 > memberOf: cn=testgroup,ou=Group,dc=example,dc=com
291 Note that the {{B:memberOf}} attribute is an operational attribute, so it must be
292 requested explicitly.
295 H2: The Proxy Cache Engine
297 {{TERM:LDAP}} servers typically hold one or more subtrees of a
298 {{TERM:DIT}}. Replica (or shadow) servers hold shadow copies of
299 entries held by one or more master servers. Changes are propagated
300 from the master server to replica (slave) servers using LDAP Sync
301 replication. An LDAP cache is a special type of replica which holds
302 entries corresponding to search filters instead of subtrees.
306 The proxy cache extension of slapd is designed to improve the
307 responsiveness of the ldap and meta backends. It handles a search
309 by first determining whether it is contained in any cached search
310 filter. Contained requests are answered from the proxy cache's local
311 database. Other requests are passed on to the underlying ldap or
312 meta backend and processed as usual.
314 E.g. {{EX:(shoesize>=9)}} is contained in {{EX:(shoesize>=8)}} and
315 {{EX:(sn=Richardson)}} is contained in {{EX:(sn=Richards*)}}
317 Correct matching rules and syntaxes are used while comparing
318 assertions for query containment. To simplify the query containment
319 problem, a list of cacheable "templates" (defined below) is specified
320 at configuration time. A query is cached or answered only if it
321 belongs to one of these templates. The entries corresponding to
322 cached queries are stored in the proxy cache local database while
323 its associated meta information (filter, scope, base, attributes)
324 is stored in main memory.
326 A template is a prototype for generating LDAP search requests.
327 Templates are described by a prototype search filter and a list of
328 attributes which are required in queries generated from the template.
329 The representation for prototype filter is similar to {{REF:RFC4515}},
330 except that the assertion values are missing. Examples of prototype
331 filters are: (sn=),(&(sn=)(givenname=)) which are instantiated by
332 search filters (sn=Doe) and (&(sn=Doe)(givenname=John)) respectively.
334 The cache replacement policy removes the least recently used (LRU)
335 query and entries belonging to only that query. Queries are allowed
336 a maximum time to live (TTL) in the cache thus providing weak
337 consistency. A background task periodically checks the cache for
338 expired queries and removes them.
340 The Proxy Cache paper
341 ({{URL:http://www.openldap.org/pub/kapurva/proxycaching.pdf}}) provides
342 design and implementation details.
345 H3: Proxy Cache Configuration
347 The cache configuration specific directives described below must
348 appear after a {{EX:overlay proxycache}} directive within a
349 {{EX:"database meta"}} or {{EX:database ldap}} section of
350 the server's {{slapd.conf}}(5) file.
352 H4: Setting cache parameters
354 > proxyCache <DB> <maxentries> <nattrsets> <entrylimit> <period>
356 This directive enables proxy caching and sets general cache
357 parameters. The <DB> parameter specifies which underlying database
358 is to be used to hold cached entries. It should be set to
359 {{EX:bdb}} or {{EX:hdb}}. The <maxentries> parameter specifies the
360 total number of entries which may be held in the cache. The
361 <nattrsets> parameter specifies the total number of attribute sets
362 (as specified by the {{EX:proxyAttrSet}} directive) that may be
363 defined. The <entrylimit> parameter specifies the maximum number of
364 entries in a cacheable query. The <period> specifies the consistency
365 check period (in seconds). In each period, queries with expired
368 H4: Defining attribute sets
370 > proxyAttrset <index> <attrs...>
372 Used to associate a set of attributes to an index. Each attribute
373 set is associated with an index number from 0 to <numattrsets>-1.
374 These indices are used by the proxyTemplate directive to define
377 H4: Specifying cacheable templates
379 > proxyTemplate <prototype_string> <attrset_index> <TTL>
381 Specifies a cacheable template and the "time to live" (in sec) <TTL>
382 for queries belonging to the template. A template is described by
383 its prototype filter string and set of required attributes identified
389 An example {{slapd.conf}}(5) database section for a caching server
390 which proxies for the {{EX:"dc=example,dc=com"}} subtree held
391 at server {{EX:ldap.example.com}}.
394 > suffix "dc=example,dc=com"
395 > rootdn "dc=example,dc=com"
396 > uri ldap://ldap.example.com/dc=example%2cdc=com
398 > proxycache bdb 100000 1 1000 100
399 > proxyAttrset 0 mail postaladdress telephonenumber
400 > proxyTemplate (sn=) 0 3600
401 > proxyTemplate (&(sn=)(givenName=)) 0 3600
402 > proxyTemplate (&(departmentNumber=)(secretary=*)) 0 3600
405 > directory ./testrun/db.2.a
406 > index objectClass eq
407 > index cn,sn,uid,mail pres,eq,sub
410 H5: Cacheable Queries
412 A LDAP search query is cacheable when its filter matches one of the
413 templates as defined in the "proxyTemplate" statements and when it references
414 only the attributes specified in the corresponding attribute set.
415 In the example above the attribute set number 0 defines that only the
416 attributes: {{EX:mail postaladdress telephonenumber}} are cached for the following
421 > Filter: (&(sn=Richard*)(givenName=jack))
422 > Attrs: mail telephoneNumber
424 is cacheable, because it matches the template {{EX:(&(sn=)(givenName=))}} and its
425 attributes are contained in proxyAttrset 0.
427 > Filter: (&(sn=Richard*)(telephoneNumber))
430 is not cacheable, because the filter does not match the template,
431 nor is the attribute givenName stored in the cache
433 > Filter: (|(sn=Richard*)(givenName=jack))
434 > Attrs: mail telephoneNumber
436 is not cacheable, because the filter does not match the template ( logical
437 OR "|" condition instead of logical AND "&" )
440 H2: Password Policies
445 This overlay provides a variety of password control mechanisms,
446 e.g. password aging, password reuse and duplication control, mandatory
447 password resets, etc.
450 H3: Password Policy Configuration
453 H2: Referential Integrity
458 This overlay can be used with a backend database such as slapd-bdb (5)
459 to maintain the cohesiveness of a schema which utilizes reference
463 H3: Referential Integrity Configuration
471 This overlay is useful to test the behavior of clients when
472 server-generated erroneous and/or unusual responses occur.
475 H3: Return Code Configuration
483 It performs basic DN/data rewrite and
484 objectClass/attributeType mapping.
487 H3: Rewrite/Remap Configuration
495 This overlay implements the provider-side support for syncrepl
496 replication, including persistent search functionality
499 H3: Sync Provider Configuration
502 H2: Translucent Proxy
507 This overlay can be used with a backend database such as slapd-bdb (5)
508 to create a "translucent proxy".
510 Content of entries retrieved from a remote LDAP server can be partially
511 overridden by the database.
514 H3: Translucent Proxy Configuration
517 H2: Attribute Uniqueness
522 This overlay can be used with a backend database such as slapd-bdb (5)
523 to enforce the uniqueness of some or all attributes within a subtree.
526 H3: Attribute Uniqueness Configuration
534 This overlay can be used to enforce a specific order for the values
535 of an attribute when it is returned in a search.
538 H3: Value Sorting Configuration
547 H3: Example Scenarios