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<modulesynopsis metafile="mod_ldap.xml.meta">

<name>mod_ldap</name>

<description>LDAP connection pooling and result caching services for use

by other LDAP modules</description>

<status>Experimental</status>

<sourcefile>util_ldap.c</sourcefile>

<identifier>ldap_module</identifier>

<compatibility>Available in version 2.0.41 and later</compatibility>

<summary>

<p>This module was created to improve the performance of

websites relying on backend connections to LDAP servers. In

addition to the functions provided by the standard LDAP

libraries, this module adds an LDAP connection pool and an LDAP

shared memory cache.</p>

<p>To enable this module, LDAP support must be compiled into

apr-util. This is achieved by adding the <code>--with-ldap</code>

flag to the <program>configure</program> script when building

Apache.</p>

<p>SSL support requires that <module>mod_ldap</module> be linked

with one of the following LDAP SDKs: <a href="http://www.openldap.org/">

OpenLDAP SDK</a> (both 1.x and 2.x), <a href="http://developer.novell.com/ndk/cldap.htm">

Novell LDAP SDK</a> or the <a href="http://www.iplanet.com/downloads/developer/">

iPlanet(Netscape)</a> SDK.</p>

</summary>

<section id="exampleconfig"><title>Example Configuration</title>

<p>The following is an example configuration that uses

<module>mod_ldap</module> to increase the performance of HTTP Basic

authentication provided by <module>mod_authnz_ldap</module>.</p>

<example>

# Enable the LDAP connection pool and shared<br />

# memory cache. Enable the LDAP cache status<br />

# handler. Requires that mod_ldap and mod_authnz_ldap<br />

# be loaded. Change the "yourdomain.example.com" to<br />

# match your domain.<br />

<br />

LDAPSharedCacheSize 200000<br />

LDAPCacheEntries 1024<br />

LDAPCacheTTL 600<br />

LDAPOpCacheEntries 1024<br />

LDAPOpCacheTTL 600<br />

<br />

&lt;Location /ldap-status&gt;<br />

<indent>

SetHandler ldap-status<br />

Order deny,allow<br />

Deny from all<br />

Allow from yourdomain.example.com<br />

AuthLDAPEnabled on<br />

AuthLDAPURL ldap://127.0.0.1/dc=example,dc=com?uid?one<br />

AuthLDAPAuthoritative on<br />

require valid-user<br />

</indent>

&lt;/Location&gt;

</example>

</section>

<section id="pool"><title>LDAP Connection Pool</title>

<p>LDAP connections are pooled from request to request. This

allows the LDAP server to remain connected and bound ready for

the next request, without the need to unbind/connect/rebind.

The performance advantages are similar to the effect of HTTP

keepalives.</p>

<p>On a busy server it is possible that many requests will try

and access the same LDAP server connection simultaneously.

Where an LDAP connection is in use, Apache will create a new

connection alongside the original one. This ensures that the

connection pool does not become a bottleneck.</p>

<p>There is no need to manually enable connection pooling in

the Apache configuration. Any module using this module for

access to LDAP services will share the connection pool.</p>

</section>

<section id="cache"><title>LDAP Cache</title>

<p>For improved performance, <module>mod_ldap</module> uses an aggressive

caching strategy to minimize the number of times that the LDAP

server must be contacted. Caching can easily double or triple

the throughput of Apache when it is serving pages protected

with mod_authnz_ldap. In addition, the load on the LDAP server

will be significantly decreased.</p>

<p><module>mod_ldap</module> supports two types of LDAP caching during

the search/bind phase with a <em>search/bind cache</em> and

during the compare phase with two <em>operation

caches</em>. Each LDAP URL that is used by the server has

its own set of these three caches.</p>

<section id="search-bind"><title>The Search/Bind Cache</title>

<p>The process of doing a search and then a bind is the

most time-consuming aspect of LDAP operation, especially if

the directory is large. The search/bind cache is used to

cache all searches that resulted in successful binds.

Negative results (<em>i.e.</em>, unsuccessful searches, or searches

that did not result in a successful bind) are not cached.

The rationale behind this decision is that connections with

invalid credentials are only a tiny percentage of the total

number of connections, so by not caching invalid

credentials, the size of the cache is reduced.</p>

<p><module>mod_ldap</module> stores the username, the DN

retrieved, the password used to bind, and the time of the bind

in the cache. Whenever a new connection is initiated with the

same username, <module>mod_ldap</module> compares the password

of the new connection with the password in the cache. If the

passwords match, and if the cached entry is not too old,

<module>mod_ldap</module> bypasses the search/bind phase.</p>

<p>The search and bind cache is controlled with the <directive

module="mod_ldap">LDAPCacheEntries</directive> and <directive

module="mod_ldap">LDAPCacheTTL</directive> directives.</p>

</section>

<section id="opcaches"><title>Operation Caches</title>

<p>During attribute and distinguished name comparison

functions, <module>mod_ldap</module> uses two operation caches

to cache the compare operations. The first compare cache is

used to cache the results of compares done to test for LDAP

group membership. The second compare cache is used to cache

the results of comparisons done between distinguished

names.</p>

<p>The behavior of both of these caches is controlled with

the <directive module="mod_ldap">LDAPOpCacheEntries</directive>

and <directive module="mod_ldap">LDAPOpCacheTTL</directive>

directives.</p>

</section>

<section id="monitoring"><title>Monitoring the Cache</title>

<p><module>mod_ldap</module> has a content handler that allows

administrators to monitor the cache performance. The name of

the content handler is <code>ldap-status</code>, so the

following directives could be used to access the

<module>mod_ldap</module> cache information:</p>

<example>

&lt;Location /server/cache-info&gt;<br />

<indent>

SetHandler ldap-status<br />

</indent>

&lt;/Location&gt;

</example>

<p>By fetching the URL <code>http://servername/cache-info</code>,

the administrator can get a status report of every cache that is used

by <module>mod_ldap</module> cache. Note that if Apache does not

support shared memory, then each <program>httpd</program> instance has its

own cache, so reloading the URL will result in different

information each time, depending on which <program>httpd</program>

instance processes the request.</p>

</section>

</section>

<section id="usingssltls"><title>Using SSL</title>

<p>The ability to create an SSL connections to an LDAP server

is defined by the directives <directive module="mod_ldap">

LDAPTrustedCA</directive> and <directive module="mod_ldap">

LDAPTrustedCAType</directive>. These directives specify the certificate

file or database and the certificate type. Whenever the LDAP url

includes <em>ldaps://</em>, <module>mod_ldap</module> will establish

a secure connection to the LDAP server.</p>

<example>

# Establish an SSL LDAP connection. Requires that <br />

# mod_ldap and mod_authnz_ldap be loaded. Change the <br />

# "yourdomain.example.com" to match your domain.<br />

<br />

LDAPTrustedCA /certs/certfile.der<br />

LDAPTrustedCAType DER_FILE<br />

<br />

&lt;Location /ldap-status&gt;<br />

<indent>

SetHandler ldap-status<br />

Order deny,allow<br />

Deny from all<br />

Allow from yourdomain.example.com<br />

AuthLDAPEnabled on<br />

AuthLDAPURL ldaps://127.0.0.1/dc=example,dc=com?uid?one<br />

AuthLDAPAuthoritative on<br />

require valid-user<br />

</indent>

&lt;/Location&gt;

</example>

<p>If <module>mod_ldap</module> is linked against the

Netscape/iPlanet LDAP SDK, it will not talk to any SSL server

unless that server has a certificate signed by a known Certificate

Authority. As part of the configuration

<module>mod_ldap</module> needs to be told where it can find

a database containing the known CAs. This database is in the same

format as Netscape Communicator's <code>cert7.db</code>

database. The easiest way to get this file is to start up a fresh

copy of Netscape, and grab the resulting

<code>$HOME/.netscape/cert7.db</code> file.</p>

</section>

<directivesynopsis>

<name>LDAPSharedCacheSize</name>

<description>Size in bytes of the shared-memory cache</description>

<syntax>LDAPSharedCacheSize <var>bytes</var></syntax>

<default>LDAPSharedCacheSize 102400</default>

<contextlist><context>server config</context></contextlist>

<usage>

<p>Specifies the number of bytes to allocate for the shared

memory cache. The default is 100kb. If set to 0, shared memory

caching will not be used.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>LDAPSharedCacheFile</name>

<description>Sets the shared memory cache file</description>

<syntax>LDAPSharedCacheFile <var>directory-path/filename</var></syntax>

<contextlist><context>server config</context></contextlist>

<usage>

<p>Specifies the directory path and file name of the shared memory

cache file. If not set, anonymous shared memory will be used if the

platform supports it.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>LDAPCacheEntries</name>

<description>Maximum number of entries in the primary LDAP cache</description>

<syntax>LDAPCacheEntries <var>number</var></syntax>

<default>LDAPCacheEntries 1024</default>

<contextlist><context>server config</context></contextlist>

<usage>

<p>Specifies the maximum size of the primary LDAP cache. This

cache contains successful search/binds. Set it to 0 to turn off

search/bind caching. The default size is 1024 cached

searches.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>LDAPCacheTTL</name>

<description>Time that cached items remain valid</description>

<syntax>LDAPCacheTTL <var>seconds</var></syntax>

<default>LDAPCacheTTL 600</default>

<contextlist><context>server config</context></contextlist>

<usage>

<p>Specifies the time (in seconds) that an item in the

search/bind cache remains valid. The default is 600 seconds (10

minutes).</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>LDAPOpCacheEntries</name>

<description>Number of entries used to cache LDAP compare

operations</description>

<syntax>LDAPOpCacheEntries <var>number</var></syntax>

<default>LDAPOpCacheEntries 1024</default>

<contextlist><context>server config</context></contextlist>

<usage>

<p>This specifies the number of entries <module>mod_ldap</module>

will use to cache LDAP compare operations. The default is 1024

entries. Setting it to 0 disables operation caching.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>LDAPOpCacheTTL</name>

<description>Time that entries in the operation cache remain

valid</description>

<syntax>LDAPOpCacheTTL <var>seconds</var></syntax>

<default>LDAPOpCacheTTL 600</default>

<contextlist><context>server config</context></contextlist>

<usage>

<p>Specifies the time (in seconds) that entries in the

operation cache remain valid. The default is 600 seconds.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>LDAPTrustedCA</name>

<description>Sets the file containing the trusted Certificate Authority certificate or database</description>

<syntax>LDAPTrustedCA <var>directory-path/filename</var></syntax>

<contextlist><context>server config</context></contextlist>

<usage>

<p>It specifies the directory path and file name of the trusted CA

<module>mod_ldap</module> should use when establishing an SSL

connection to an LDAP server. If using the Netscape/iPlanet Directory

SDK, the file name should be <code>cert7.db</code>.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>LDAPTrustedCAType</name>

<description>Specifies the type of the Certificate Authority file</description>

<syntax>LDAPTrustedCAType <var>type</var></syntax>

<contextlist><context>server config</context></contextlist>

<usage>

<p>The following types are supported:<br />

DER_FILE - file in binary DER format<br />

BASE64_FILE - file in Base64 format<br />

CERT7_DB_PATH - Netscape certificate database file ")</p>

</usage>

</directivesynopsis>

</modulesynopsis>