1SLAPO-PCACHE(5) File Formats Manual SLAPO-PCACHE(5)
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6 slapo-pcache - proxy cache overlay to slapd
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9 /etc/openldap/slapd.conf
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12 The pcache overlay to slapd(8) allows caching of LDAP search requests
13 (queries) in a local database. For an incoming query, the proxy cache
14 determines its corresponding template. If the template was specified as
15 cacheable using the pcacheTemplate directive and the request is con‐
16 tained in a cached request, it is answered from the proxy cache. Oth‐
17 erwise, the search is performed as usual and cacheable search results
18 are saved in the cache for use in future queries.
19 A template is defined by a filter string and an index identifying a set
21 of attributes. The template string for a query can be obtained by
22 removing assertion values from the RFC 4515 representation of its
23 search filter. A query belongs to a template if its template string and
24 set of projected attributes correspond to a cacheable template. Exam‐
25 ples of template strings are (mail=), (|(sn=)(cn=)), (&(sn=)(given‐
26 Name=)).
27 The config directives that are specific to the pcache overlay can be
30 prefixed by pcache-, to avoid conflicts with directives specific to the
31 underlying database or to other stacked overlays. This may be particu‐
32 larly useful for those directives that refer to the backend used for
33 local storage. The following cache specific directives can be used to
34 configure the proxy cache:
35 overlay pcache
37 This directive adds the proxy cache overlay to the current back‐
38 end. The proxy cache overlay may be used with any backend but is
39 intended for use with the ldap, meta, and sql backends. Please
40 note that the underlying backend must have a configured rootdn.
41 pcache <database> <max_entries> <numattrsets> <entry_limit> <cc_period>
43 The directive enables proxy caching in the current backend and
44 sets general cache parameters. A <database> backend will be used
45 internally to maintain the cached entries. The chosen database
46 will need to be configured as well, as shown below. Cache
47 replacement is invoked when the cache size grows to
48 <max_entries> entries and continues till the cache size drops
49 below this size. <numattrsets> should be equal to the number of
50 following pcacheAttrset directives. Queries are cached only if
51 they correspond to a cacheable template (specified by the pca‐
52 cheTemplate directive) and the number of entries returned is
53 less than <entry_limit>. Consistency check is performed every
54 <cc_period> duration (specified in secs). In each cycle queries
55 with expired "time to live(TTL)" are removed. A sample cache
56 configuration is:
57 pcache mdb 10000 1 50 100
59 pcacheAttrset <index> <attrs...>
62 Used to associate a set of attributes <attrs..> with an <index>.
63 Each attribute set is associated with an integer from 0 to
64 <numattrsets>-1. These indices are used by the pcacheTemplate
65 directive to define cacheable templates. A set of attributes
66 cannot be empty. A set of attributes can contain the special
67 attributes "*" (all user attributes), "+" (all operational
68 attributes) or both; in the latter case, any other attribute is
69 redundant and should be avoided for clarity. A set of
70 attributes can contain "1.1" as the only attribute; in this
71 case, only the presence of the entries is cached. Attributes
72 prefixed by "undef:" need not be present in the schema.
73 pcacheMaxQueries <queries>
76 Specify the maximum number of queries to cache. The default is
77 10000.
78 pcacheValidate { TRUE | FALSE }
81 Check whether the results of a query being cached can actually
82 be returned from the cache by the proxy DSA. When enabled, the
83 entries being returned while caching the results of a query are
84 checked to ensure consistency with the schema known to the proxy
85 DSA. In case of failure, the query is not cached. By default,
86 the check is off.
87 pcacheOffline { TRUE | FALSE }
90 Set the cache to offline mode. While offline, the consistency
91 checker will be stopped and no expirations will occur. This
92 allows the cache contents to be used indefinitely while the
93 proxy is cut off from network access to the remote DSA. The
94 default is FALSE, i.e. consistency checks and expirations will
95 be performed.
96 pcachePersist { TRUE | FALSE }
99 Specify whether the cached queries should be saved across
100 restarts of the caching proxy, to provide hot startup of the
101 cache. Only non-expired queries are reloaded. The default is
102 FALSE.
103 CAVEAT: of course, the configuration of the proxy cache must not
105 change across restarts; the pcache overlay does not perform any
106 consistency checks in this sense. In detail, this option should
107 be disabled unless the existing pcacheAttrset and pcacheTemplate
108 directives are not changed neither in order nor in contents. If
109 new sets and templates are added, or if other details of the
110 pcache overlay configuration changed, this feature should not be
111 affected.
112 pcacheTemplate <template_string> <attrset_index> <ttl> [<negttl>
115 [<limitttl> [<ttr>]]]
116 Specifies a cacheable template and "time to live" <ttl> of
117 queries belonging to the template. An optional <negttl> can be
118 used to specify that negative results (i.e., queries that
119 returned zero entries) should also be cached for the specified
120 amount of time. Negative results are not cached by default
121 (<negttl> set to 0). An optional <limitttl> can be used to
122 specify that results hitting a sizelimit should also be cached
123 for the specified amount of time. Results hitting a sizelimit
124 are not cached by default (<limitttl> set to 0). An optional
125 <ttr> "time to refresh" can be used to specify that cached
126 entries should be automatically refreshed after a certain time.
127 Entries will only be refreshed while they have not expired, so
128 the <ttl> should be larger than the <ttr> for this option to be
129 useful. Entries are not refreshed by default (<ttr> set to 0).
130 pcacheBind <filter_template> <attrset_index> <ttr> <scope> <base>
133 Specifies a template for caching Simple Bind credentials based
134 on an already defined pcacheTemplate. The <filter_template> is
135 similar to a <template_string> except that it may have some val‐
136 ues present. Its purpose is to allow the overlay to generate
137 filters similar to what other applications do when they do a
138 Search immediately before a Bind. E.g., if a client like
139 nss_ldap is configured to search for a user with the filter
140 "(&(objectClass=posixAccount)(uid=<username>))" then the corre‐
141 sponding template "(&(objectClass=posixAccount)(uid=))" should
142 be used here. When converted to a regular template e.g.
143 "(&(objectClass=)(uid=))" this template and the <attrset_index>
144 must match an already defined pcacheTemplate clause. The "time
145 to refresh" <ttr> determines the time interval after which the
146 cached credentials may be refreshed. The first Bind request that
147 occurs after that time will trigger the refresh attempt.
148 Refreshes are not performed when the overlay is Offline. There
149 is no "time to live" parameter for the Bind credentials; the
150 credentials will expire according to the pcacheTemplate ttl. The
151 <scope> and <base> should match the search scope and base used
152 by the authentication clients. The cached credentials are not
153 stored in cleartext, they are hashed using the default password
154 hash. By default Bind caching is not enabled.
155 pcachePosition { head | tail }
158 Specifies whether the response callback should be placed at the
159 tail (the default) or at the head (actually, wherever the stack‐
160 ing sequence would make it appear) of the callback list. This
161 affects how the overlay interacts with other overlays, since the
162 proxycache overlay should be executed as early as possible (and
163 thus configured as late as possible), to get a chance to return
164 the cached results; however, if executed early at response, it
165 would cache entries that may be later "massaged" by other data‐
166 bases and thus returned after massaging the first time, and
167 before massaging when cached.
168 There are some constraints:
171 all values must be positive;
173 <entry_limit> must be less than or equal to <max_entries>;
175 <numattrsets> attribute sets SHOULD be defined by using the
177 directive pcacheAttrset;
178 all attribute sets SHOULD be referenced by (at least) one pca‐
180 cheTemplate directive;
181 The following adds a template with filter string (&(sn=)(givenName=))
184 and attributes mail, postaladdress, telephonenumber and a TTL of 1
185 hour.
186 pcacheAttrset 0 mail postaladdress telephonenumber
188 pcacheTemplate (&(sn=)(givenName=)) 0 3600
189 Directives for configuring the underlying database must also be given,
192 as shown here:
193 directory /var/tmp/cache
195 cachesize 100
196 Any valid directives for the chosen database type may be used. Indexing
198 should be used as appropriate for the queries being handled. In addi‐
199 tion, an equality index on the pcacheQueryid attribute should be con‐
200 figured, to assist in the removal of expired query data.
201
203 The configuration keywords have been renamed and the older form is dep‐
204 recated. These older keywords are still recognized but may disappear in
205 future releases.
206 proxycache
209 use pcache
210 proxyattrset
213 use pcacheAttrset
214 proxycachequeries
217 use pcacheMaxQueries
218 proxycheckcacheability
221 use pcacheValidate
222 proxysavequeries
225 use pcachePersist
226 proxytemplate
229 use pcacheTemplate
230 response-callback
233 use pcachePosition
234
237 Caching data is prone to inconsistencies because updates on the remote
238 server will not be reflected in the response of the cache at least (and
239 at most) for the duration of the pcacheTemplate TTL. These inconsis‐
240 tencies can be minimized by careful use of the TTR.
241 The remote server should expose the objectClass attribute because the
243 underlying database that actually caches the entries may need it for
244 optimal local processing of the queries.
245 The proxy server should contain all the schema information required for
247 caching. Significantly, it needs the schema of attributes used in the
248 query templates. If the objectClass attribute is used in a query tem‐
249 plate, it needs the definition of the objectClasses of the entries it
250 is supposed to cache. It is the responsibility of the proxy adminis‐
251 trator to keep the proxy schema lined up with that of the proxied
252 server.
253 Another potential (and subtle) inconsistency may occur when data is
255 retrieved with different identities and specific per-identity access
256 control is enforced by the remote server. If data was retrieved with
257 an identity that collected only partial results because of access rules
258 enforcement on the remote server, other users with different access
259 privileges on the remote server will get different results from the
260 remote server and from the cache. If those users have higher access
261 privileges on the remote server, they will get from the cache only a
262 subset of the results they would get directly from the remote server;
263 but if they have lower access privileges, they will get from the cache
264 a superset of the results they would get directly from the remote
265 server. Either occurrence may or may not be acceptable, based on the
266 security policy of the cache and of the remote server. It is important
267 to note that in this case the proxy is violating the security of the
268 remote server by disclosing to an identity data that was collected by
269 another identity. For this reason, it is suggested that, when using
270 back-ldap, proxy caching be used in conjunction with the identity
271 assertion feature of slapd-ldap(5) (see the idassert-bind and the
272 idassert-authz statements), so that remote server interrogation occurs
273 with a vanilla identity that has some relatively high search and read
274 access privileges, and the "real" access control is delegated to the
275 proxy's ACLs. Beware that since only the cached fraction of the real
276 datum is available to the cache, it may not be possible to enforce the
277 same access rules that are defined on the remote server. When security
278 is a concern, cached proxy access must be carefully tailored.
279
281 /etc/openldap/slapd.conf
282 default slapd configuration file
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285 slapd.conf(5), slapd-config(5), slapd-ldap(5), slapd-meta(5),
286 slapd-sql(5), slapd(8).
287
289 Originally implemented by Apurva Kumar as an extension to back-meta;
290 turned into an overlay by Howard Chu.
291OpenLDAP 2.4.50 2020/04/28 SLAPO-PCACHE(5)