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
210 H3: Member Of Configuration
213 H2: The Proxy Cache Engine
215 {{TERM:LDAP}} servers typically hold one or more subtrees of a
216 {{TERM:DIT}}. Replica (or shadow) servers hold shadow copies of
217 entries held by one or more master servers. Changes are propagated
218 from the master server to replica (slave) servers using LDAP Sync
219 replication. An LDAP cache is a special type of replica which holds
220 entries corresponding to search filters instead of subtrees.
224 The proxy cache extension of slapd is designed to improve the
225 responsiveness of the ldap and meta backends. It handles a search
227 by first determining whether it is contained in any cached search
228 filter. Contained requests are answered from the proxy cache's local
229 database. Other requests are passed on to the underlying ldap or
230 meta backend and processed as usual.
232 E.g. {{EX:(shoesize>=9)}} is contained in {{EX:(shoesize>=8)}} and
233 {{EX:(sn=Richardson)}} is contained in {{EX:(sn=Richards*)}}
235 Correct matching rules and syntaxes are used while comparing
236 assertions for query containment. To simplify the query containment
237 problem, a list of cacheable "templates" (defined below) is specified
238 at configuration time. A query is cached or answered only if it
239 belongs to one of these templates. The entries corresponding to
240 cached queries are stored in the proxy cache local database while
241 its associated meta information (filter, scope, base, attributes)
242 is stored in main memory.
244 A template is a prototype for generating LDAP search requests.
245 Templates are described by a prototype search filter and a list of
246 attributes which are required in queries generated from the template.
247 The representation for prototype filter is similar to {{REF:RFC4515}},
248 except that the assertion values are missing. Examples of prototype
249 filters are: (sn=),(&(sn=)(givenname=)) which are instantiated by
250 search filters (sn=Doe) and (&(sn=Doe)(givenname=John)) respectively.
252 The cache replacement policy removes the least recently used (LRU)
253 query and entries belonging to only that query. Queries are allowed
254 a maximum time to live (TTL) in the cache thus providing weak
255 consistency. A background task periodically checks the cache for
256 expired queries and removes them.
258 The Proxy Cache paper
259 ({{URL:http://www.openldap.org/pub/kapurva/proxycaching.pdf}}) provides
260 design and implementation details.
263 H3: Proxy Cache Configuration
265 The cache configuration specific directives described below must
266 appear after a {{EX:overlay proxycache}} directive within a
267 {{EX:"database meta"}} or {{EX:database ldap}} section of
268 the server's {{slapd.conf}}(5) file.
270 H4: Setting cache parameters
272 > proxyCache <DB> <maxentries> <nattrsets> <entrylimit> <period>
274 This directive enables proxy caching and sets general cache
275 parameters. The <DB> parameter specifies which underlying database
276 is to be used to hold cached entries. It should be set to
277 {{EX:bdb}} or {{EX:hdb}}. The <maxentries> parameter specifies the
278 total number of entries which may be held in the cache. The
279 <nattrsets> parameter specifies the total number of attribute sets
280 (as specified by the {{EX:proxyAttrSet}} directive) that may be
281 defined. The <entrylimit> parameter specifies the maximum number of
282 entries in a cacheable query. The <period> specifies the consistency
283 check period (in seconds). In each period, queries with expired
286 H4: Defining attribute sets
288 > proxyAttrset <index> <attrs...>
290 Used to associate a set of attributes to an index. Each attribute
291 set is associated with an index number from 0 to <numattrsets>-1.
292 These indices are used by the proxyTemplate directive to define
295 H4: Specifying cacheable templates
297 > proxyTemplate <prototype_string> <attrset_index> <TTL>
299 Specifies a cacheable template and the "time to live" (in sec) <TTL>
300 for queries belonging to the template. A template is described by
301 its prototype filter string and set of required attributes identified
307 An example {{slapd.conf}}(5) database section for a caching server
308 which proxies for the {{EX:"dc=example,dc=com"}} subtree held
309 at server {{EX:ldap.example.com}}.
312 > suffix "dc=example,dc=com"
313 > rootdn "dc=example,dc=com"
314 > uri ldap://ldap.example.com/dc=example%2cdc=com
316 > proxycache bdb 100000 1 1000 100
317 > proxyAttrset 0 mail postaladdress telephonenumber
318 > proxyTemplate (sn=) 0 3600
319 > proxyTemplate (&(sn=)(givenName=)) 0 3600
320 > proxyTemplate (&(departmentNumber=)(secretary=*)) 0 3600
323 > directory ./testrun/db.2.a
324 > index objectClass eq
325 > index cn,sn,uid,mail pres,eq,sub
328 H5: Cacheable Queries
330 A LDAP search query is cacheable when its filter matches one of the
331 templates as defined in the "proxyTemplate" statements and when it references
332 only the attributes specified in the corresponding attribute set.
333 In the example above the attribute set number 0 defines that only the
334 attributes: {{EX:mail postaladdress telephonenumber}} are cached for the following
339 > Filter: (&(sn=Richard*)(givenName=jack))
340 > Attrs: mail telephoneNumber
342 is cacheable, because it matches the template {{EX:(&(sn=)(givenName=))}} and its
343 attributes are contained in proxyAttrset 0.
345 > Filter: (&(sn=Richard*)(telephoneNumber))
348 is not cacheable, because the filter does not match the template,
349 nor is the attribute givenName stored in the cache
351 > Filter: (|(sn=Richard*)(givenName=jack))
352 > Attrs: mail telephoneNumber
354 is not cacheable, because the filter does not match the template ( logical
355 OR "|" condition instead of logical AND "&" )
358 H2: Password Policies
363 This overlay provides a variety of password control mechanisms,
364 e.g. password aging, password reuse and duplication control, mandatory
365 password resets, etc.
368 H3: Password Policy Configuration
371 H2: Referential Integrity
376 This overlay can be used with a backend database such as slapd-bdb (5)
377 to maintain the cohesiveness of a schema which utilizes reference
381 H3: Referential Integrity Configuration
389 This overlay is useful to test the behavior of clients when
390 server-generated erroneous and/or unusual responses occur.
393 H3: Return Code Configuration
401 It performs basic DN/data rewrite and
402 objectClass/attributeType mapping.
405 H3: Rewrite/Remap Configuration
413 This overlay implements the provider-side support for syncrepl
414 replication, including persistent search functionality
417 H3: Sync Provider Configuration
420 H2: Translucent Proxy
425 This overlay can be used with a backend database such as slapd-bdb (5)
426 to create a "translucent proxy".
428 Content of entries retrieved from a remote LDAP server can be partially
429 overridden by the database.
432 H3: Translucent Proxy Configuration
435 H2: Attribute Uniqueness
440 This overlay can be used with a backend database such as slapd-bdb (5)
441 to enforce the uniqueness of some or all attributes within a subtree.
444 H3: Attribute Uniqueness Configuration
452 This overlay can be used to enforce a specific order for the values
453 of an attribute when it is returned in a search.
456 H3: Value Sorting Configuration
465 H3: Example Scenarios