path: root/docs/manual/mod/mod_ldap.xml

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<modulesynopsis>

<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 <code>./configure</code> script when building
    Apache.</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_auth_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_auth_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_auth_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 <code>httpd</code> instance has its
      own cache, so reloading the URL will result in different
      information each time, depending on which <code>httpd</code>
      instance processes the request.</p>
    </section>
</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 specify for the shared
    memory cache. The default is 100kb.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>LDAPCacheEntries</name>
<description>Maximum number of entires 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>LDAPCertDBPath</name>
<description>Directory containing certificates for SSL support</description>
<syntax>LDAPCertDBPath <var>directory-path</var></syntax>
<contextlist><context>server config</context></contextlist>

<usage>
    <p>This directive is only valid if Apache has been linked
    against the Netscape/iPlanet Directory SDK.</p>

    <p>It specifies in which directory <module>mod_ldap</module>
    should look for the certificate authorities database for SSL
    support. There should be a file named <code>cert7.db</code> in that
    directory.</p>
</usage>
</directivesynopsis>

</modulesynopsis>