Apache HTTP Server Version 2.0
Apache HTTP Server Version 2.0
| Description: | LDAP connection pooling and result caching services for use by other LDAP modules |
|---|---|
| Status: | Experimental |
| Module Identifier: | ldap_module |
| Source File: | util_ldap.c |
| Compatibility: | Available in version 2.0.41 and later |
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.
To enable this module, LDAP support must be compiled into
apr-util. This is achieved by adding the --with-ldap
flag to the ./configure script when building
Apache.
The following is an example configuration that uses
mod_ldap to increase the performance of HTTP Basic
authentication provided by mod_auth_ldap.
# Enable the LDAP connection pool and shared
# memory cache. Enable the LDAP cache status
# handler. Requires that mod_ldap and mod_auth_ldap
# be loaded. Change the "yourdomain.example.com" to
# match your domain.
LDAPSharedCacheSize 200000
LDAPCacheEntries 1024
LDAPCacheTTL 600
LDAPOpCacheEntries 1024
LDAPOpCacheTTL 600
<Location /ldap-status>
SetHandler ldap-status
Order deny,allow
Deny from all
Allow from yourdomain.example.com
AuthLDAPEnabled on
AuthLDAPURL ldap://127.0.0.1/dc=example,dc=com?uid?one
AuthLDAPAuthoritative on
require valid-user
</Location>
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.
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.
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.
For improved performance, mod_ldap 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.
mod_ldap supports two types of LDAP caching during
the search/bind phase with a search/bind cache and
during the compare phase with two operation
caches. Each LDAP URL that is used by the server has
its own set of these three caches.
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 (i.e., 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.
mod_ldap 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, mod_ldap 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,
mod_ldap bypasses the search/bind phase.
The search and bind cache is controlled with the LDAPCacheEntries and LDAPCacheTTL directives.
During attribute and distinguished name comparison
functions, mod_ldap 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.
The behavior of both of these caches is controlled with
the LDAPOpCacheEntries
and LDAPOpCacheTTL
directives.
mod_ldap has a content handler that allows
administrators to monitor the cache performance. The name of
the content handler is ldap-status, so the
following directives could be used to access the
mod_ldap cache information:
<Location /server/cache-info>
SetHandler ldap-status
</Location>
By fetching the URL http://servername/cache-info,
the administrator can get a status report of every cache that is used
by mod_ldap cache. Note that if Apache does not
support shared memory, then each httpd instance has its
own cache, so reloading the URL will result in different
information each time, depending on which httpd
instance processes the request.
| Description: | Maximum number of entires in the primary LDAP cache |
|---|---|
| Syntax: | LDAPCacheEntries number |
| Default: | LDAPCacheEntries 1024 |
| Context: | server config |
| Status: | Experimental |
| Module: | mod_ldap |
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.
| Description: | Time that cached items remain valid |
|---|---|
| Syntax: | LDAPCacheTTL seconds |
| Default: | LDAPCacheTTL 600 |
| Context: | server config |
| Status: | Experimental |
| Module: | mod_ldap |
Specifies the time (in seconds) that an item in the search/bind cache remains valid. The default is 600 seconds (10 minutes).
| Description: | Directory containing certificates for SSL support |
|---|---|
| Syntax: | LDAPCertDBPath directory-path |
| Context: | server config |
| Status: | Experimental |
| Module: | mod_ldap |
This directive is only valid if Apache has been linked against the Netscape/iPlanet Directory SDK.
It specifies in which directory mod_ldap
should look for the certificate authorities database for SSL
support. There should be a file named cert7.db in that
directory.
| Description: | Number of entries used to cache LDAP compare operations |
|---|---|
| Syntax: | LDAPOpCacheEntries number |
| Default: | LDAPOpCacheEntries 1024 |
| Context: | server config |
| Status: | Experimental |
| Module: | mod_ldap |
This specifies the number of entries mod_ldap
will use to cache LDAP compare operations. The default is 1024
entries. Setting it to 0 disables operation caching.
| Description: | Time that entries in the operation cache remain valid |
|---|---|
| Syntax: | LDAPOpCacheTTL seconds |
| Default: | LDAPOpCacheTTL 600 |
| Context: | server config |
| Status: | Experimental |
| Module: | mod_ldap |
Specifies the time (in seconds) that entries in the operation cache remain valid. The default is 600 seconds.
| Description: | Size in bytes of the shared-memory cache |
|---|---|
| Syntax: | LDAPSharedCacheSize bytes |
| Default: | LDAPSharedCacheSize 102400 |
| Context: | server config |
| Status: | Experimental |
| Module: | mod_ldap |
Specifies the number of bytes to specify for the shared memory cache. The default is 100kb.
