# $OpenLDAP: pkg/openldap-guide/admin/backends.sdf,v 1.8.2.10 2011/01/04 23:49:38 kurt Exp $
# Copyright 2007-2011 The OpenLDAP Foundation, All Rights Reserved.
# COPYING RESTRICTIONS APPLY, see COPYRIGHT.

H1: Backends

Backends do the actual work of storing or retrieving data in response
to LDAP requests. Backends may be compiled statically into {{slapd}},
or when module support is enabled, they may be dynamically loaded.

If your installation uses dynamic modules, you may need to add the
relevant {{moduleload}} directives to the examples that follow. The
name of the module for a backend is usually of the form:

>	back_<backend name>.la

So for example, if you need to load the {{hdb}} backend, you would configure

>	moduleload back_hdb.la

H2: Berkeley DB Backends


H3: Overview

The {{bdb}} backend to {{slapd}}(8) is the recommended primary backend for a 
normal {{slapd}} database.  It uses the Oracle Berkeley DB ({{TERM:BDB}}) 
package to store data. It makes extensive use of indexing and caching 
(see the {{SECT:Tuning}} section) to speed data access.

{{hdb}} is a variant of the {{bdb}} backend that uses a hierarchical database 
layout which supports subtree renames. It is otherwise identical to the {{bdb}}
 behavior, and all the same configuration options apply.

Note: An {{hdb}} database needs a large {{idlcachesize}} for good search performance, 
typically three times the {{cachesize}} (entry cache size) or larger.

H3: back-bdb/back-hdb Configuration

MORE LATER

H3: Further Information

{{slapd-bdb}}(5)

H2: LDAP


H3: Overview

The LDAP backend to {{slapd}}(8) is not an actual database; instead it acts 
as a proxy to forward incoming requests to another LDAP server. While 
processing requests it will also chase referrals, so that referrals are fully
processed instead of being returned to the {{slapd}} client.

Sessions that explicitly {{Bind}} to the {{back-ldap}} database always create 
their own private connection to the remote LDAP server. Anonymous sessions 
will share a single anonymous connection to the remote server. For sessions 
bound through other mechanisms, all sessions with the same DN will share the 
same connection. This connection pooling strategy can enhance the proxy's 
efficiency by reducing the overhead of repeatedly making/breaking multiple 
connections.

The ldap database can also act as an information service, i.e. the identity 
of locally authenticated clients is asserted to the remote server, possibly 
in some modified form. For this purpose, the proxy binds to the remote server 
with some administrative identity, and, if required, authorizes the asserted 
identity. 

It is heavily used by a lot of other {{SECT: Backends}} and {{SECT: Overlays}}.

H3: back-ldap Configuration

As previously mentioned, {{slapd-ldap(5)}} is used behind the scenes by many 
other {{SECT: Backends}} and {{SECT: Overlays}}. Some of them merely provide a 
few configuration directive themselves, but have available to the administrator
the whole of the {{slapd-ldap(5)}} options. 

For example, the {{SECT: Translucent Proxy}}, which retrieves entries from a 
remote LDAP server that can be partially overridden by the defined database, has
only four specific {{translucent-}} directives, but can be configured using any 
of the normal {{slapd-ldap(5)}} options. See {[slapo-translucent(5)}} for details.

Other {{SECT: Overlays}} allow you to tag directives in front of a normal 
{{slapd-ldap(5)}} directive. For example, the {{slapo-chain(5)}} overlay does 
this:

{{"There are very few chain overlay specific directives; however, directives 
related to the instances of the ldap backend that may be implicitly instantiated 
by the overlay may assume a special meaning when used in conjunction with this 
overlay.  They are described in slapd-ldap(5), and they also need to be prefixed 
by chain-."}}

You may have also seen the {{slapd-ldap(5)}} backend used and described in the
{{SECT: Push Based}} {{SECT: Replication}} section of the guide.

It should therefore be obvious that the {{slapd-ldap(5)}} backend is extremely
flexible and heavily used throughout the OpenLDAP Suite.

The following is a very simple example, but already the power of the {{slapd-ldap(5)}}
backend is seen by use of a {{uri list}}:

>	database        ldap
>	suffix          "dc=suretecsystems,dc=com"
>	rootdn          "cn=slapd-ldap"
>	uri             ldap://localhost/ ldap://remotehost ldap://remotehost2

The URI list is space or comma-separated. Whenever the server that responds 
is not the first one in the list, the list is rearranged and the responsive 
server is moved to the head, so that it will be first contacted the next time 
a connection needs be created.

This feature can be used to provide a form of load balancing when using 
{{SECT: MirrorMode replication}}.

H3: Further Information

{{slapd-ldap}}(5)

H2: LDIF


H3: Overview

The LDIF backend to {{slapd}}(8) is a basic storage backend that stores 
entries in text files in LDIF format, and exploits the filesystem to create 
the tree structure of the database. It is intended as a cheap, low performance 
easy to use backend.

When using the {{cn=config}} dynamic configuration database with persistent
storage, the configuration data is stored using this backend. See {{slapd-config}}(5)
for more information

H3: back-ldif Configuration

Like many other backends, the LDIF backend can be instantiated with very few
configuration lines:

>	include ./schema/core.schema
>	
>	database  ldif
>	directory "./ldif"
>	suffix    "dc=suretecsystems,dc=com"
>	rootdn    "cn=LDIF,dc=suretecsystems,dc=com"
>	rootpw    LDIF

If we add the {{dcObject}} for {{dc=suretecsystems,dc=com}}, you can see how this
is added behind the scenes on the file system:

>   dn: dc=suretecsystems,dc=com
>   objectClass: dcObject
>   objectClass: organization
>   dc: suretecsystems
>   o: Suretec Systems Ltd

Now we add it to the directory:

>   ldapadd -x -H ldap://localhost:9011 -f suretec.ldif -D "cn=LDIF,dc=suretecsystems,dc=com" -w LDIF
>   adding new entry "dc=suretecsystems,dc=com"

And inside {{F: ./ldif}} we have:

>   ls ./ldif
>   dc=suretecsystems,dc=com.ldif

which again contains:

>   cat ldif/dc\=suretecsystems\,dc\=com.ldif 
>   
>   dn: dc=suretecsystems
>   objectClass: dcObject
>   objectClass: organization
>   dc: suretecsystems
>   o: Suretec Systems Ltd.
>   structuralObjectClass: organization
>   entryUUID: 2134b714-e3a1-102c-9a15-f96ee263886d
>   creatorsName: cn=LDIF,dc=suretecsystems,dc=com
>   createTimestamp: 20080711142643Z
>   entryCSN: 20080711142643.661124Z#000000#000#000000
>   modifiersName: cn=LDIF,dc=suretecsystems,dc=com
>   modifyTimestamp: 20080711142643Z

This is the complete format you would get when exporting your directory using
{{F: slapcat}} etc.

H3: Further Information

{{slapd-ldif}}(5)

H2: Metadirectory


H3: Overview

The meta backend to {{slapd}}(8) performs basic LDAP proxying with respect 
to a set of remote LDAP servers, called "targets". The information contained 
in these servers can be presented as belonging to a single Directory Information 
Tree ({{TERM:DIT}}).

A basic knowledge of the functionality of the {{slapd-ldap}}(5) backend is 
recommended. This backend has been designed as an enhancement of the ldap 
backend. The two backends share many features (actually they also share portions
 of code). While the ldap backend is intended to proxy operations directed 
 to a single server, the meta backend is mainly intended for proxying of 
 multiple servers and possibly naming context  masquerading.

These features, although useful in many scenarios, may result in excessive 
overhead for some applications, so its use should be carefully considered.


H3: back-meta Configuration

LATER

H3: Further Information

{{slapd-meta}}(5)

H2: Monitor


H3: Overview

The monitor backend to {{slapd}}(8) is not an actual database; if enabled, 
it is automatically generated and dynamically maintained by slapd with 
information about the running status of the daemon.

To inspect all monitor information, issue a subtree search with base {{cn=Monitor}}, 
requesting that attributes "+" and "*" are returned. The monitor backend produces 
mostly operational attributes, and LDAP only returns operational attributes 
that are explicitly requested.  Requesting attribute "+" is an extension which 
requests all operational attributes.

See the {{SECT:Monitoring}} section.

H3: back-monitor Configuration

The monitor database can be instantiated only once, i.e. only one occurrence 
of "database monitor" can occur in the {{slapd.conf(5)}} file.  Also the suffix 
is automatically set to {{"cn=Monitor"}}.

You can however set a {{rootdn}} and {{rootpw}}. The following is all that is
needed to instantiate a monitor backend:

>	include ./schema/core.schema
>	
>	database monitor
>	rootdn "cn=monitoring,cn=Monitor"
>	rootpw monitoring

You can also apply Access Control to this database like any other database, for 
example:

>	access to dn.subtree="cn=Monitor"
>	     by dn.exact="uid=Admin,dc=my,dc=org" write
>	     by users read
>	     by * none

Note: The {{F: core.schema}} must be loaded for the monitor database to work. 

A small example of the data returned via {{ldapsearch}} would be:

>	ldapsearch -x -H ldap://localhost:9011 -b 'cn=Monitor'
>	# extended LDIF
>	#
>	# LDAPv3
>	# base <cn=Monitor> with scope subtree
>	# filter: (objectclass=*)
>	# requesting: ALL
>	#
>	
>	# Monitor
>	dn: cn=Monitor
>	objectClass: monitorServer
>	cn: Monitor
>	description: This subtree contains monitoring/managing objects.
>	description: This object contains information about this server.
>	description: Most of the information is held in operational attributes, which 
>	 must be explicitly requested.
>	
>	# Backends, Monitor
>	dn: cn=Backends,cn=Monitor
>	objectClass: monitorContainer
>	cn: Backends
>	description: This subsystem contains information about available backends.

Please see the {{SECT: Monitoring}} section for complete examples of information
available via this backend.

H3: Further Information

{{slapd-monitor}}(5)

H2: Null


H3: Overview

The Null backend to {{slapd}}(8) is surely the most useful part of slapd:

* Searches return success but no entries.
* Compares return compareFalse.
* Updates return success (unless readonly is on) but do nothing.
* Binds other than as the rootdn fail unless the database option "bind on" is given.
* The slapadd(8) and slapcat(8) tools are equally exciting.

Inspired by the {{F:/dev/null}} device.

H3: back-null Configuration

This has to be one of the shortest configurations you'll ever do. In order to 
test this, your {{F: slapd.conf}} file would look like:

>	database null
>	suffix "cn=Nothing"
>	bind on

{{bind on}} means:

{{"Allow binds as any DN in this backend's suffix, with any password. The default is "off"."}}

To test this backend with {{ldapsearch}}:

>	ldapsearch -x -H ldap://localhost:9011 -D "uid=none,cn=Nothing" -w testing -b 'cn=Nothing'
>	# extended LDIF
>	#
>	# LDAPv3
>	# base <cn=Nothing> with scope subtree
>	# filter: (objectclass=*)
>	# requesting: ALL
>	#
>	
>	# search result
>	search: 2
>	result: 0 Success
>	
>	# numResponses: 1


H3: Further Information

{{slapd-null}}(5)

H2: Passwd


H3: Overview

The PASSWD backend to {{slapd}}(8) serves up the user account information 
listed in the system {{passwd}}(5) file (defaulting to {{F: /etc/passwd}}).

This backend is provided for demonstration purposes only. The DN of each entry 
is "uid=<username>,<suffix>".

H3: back-passwd Configuration

The configuration using {{F: slapd.conf}} a slightly longer, but not much. For 
example:

>	include ./schema/core.schema
>	
>	database passwd
>	suffix "cn=passwd"

Again, testing this with {{ldapsearch}} would result in something like:

>	ldapsearch -x -H ldap://localhost:9011 -b 'cn=passwd'
>	# extended LDIF
>	#
>	# LDAPv3
>	# base <cn=passwd> with scope subtree
>	# filter: (objectclass=*)
>	# requesting: ALL
>	#
>	
>	# passwd
>	dn: cn=passwd
>	cn: passwd
>	objectClass: organizationalUnit
>	
>	# root, passwd
>	dn: uid=root,cn=passwd
>	objectClass: person
>	objectClass: uidObject
>	uid: root
>	cn: root
>	sn: root
>	description: root


H3: Further Information

{{slapd-passwd}}(5)

H2: Perl/Shell

H3: Overview

The Perl backend to {{slapd}}(8) works by embedding a {{perl}}(1) interpreter 
into {{slapd}}(8). Any perl database section of the configuration file 
{{slapd.conf}}(5) must then specify what Perl module to use. Slapd then creates 
a new Perl object that handles all the requests for that particular instance of the backend.

The Shell backend to {{slapd}}(8) executes external programs to implement 
operations, and is designed to make it easy to tie an existing database to the 
slapd front-end. This backend is is primarily intended to be used in prototypes.

H3: back-perl/back-shell Configuration

LATER

H3: Further Information

{{slapd-shell}}(5) and {{slapd-perl}}(5)

H2: Relay


H3: Overview

The primary purpose of this {{slapd}}(8) backend is to map a naming context 
defined in a database running in the same {{slapd}}(8) instance into a 
virtual naming context, with attributeType and objectClass manipulation, if
required. It requires the rwm overlay.

This backend and the above mentioned overlay are experimental.

H3: back-relay Configuration

LATER

H3: Further Information

{{slapd-relay}}(5)

H2: SQL


H3: Overview

The primary purpose of this {{slapd}}(8) backend is to PRESENT information 
stored in some RDBMS as an LDAP subtree without any programming (some SQL and 
maybe stored procedures can't be considered programming, anyway ;).

That is, for example, when you (some ISP) have account information you use in 
an RDBMS, and want to use modern solutions that expect such information in LDAP 
(to authenticate users, make email lookups etc.). Or you want to synchronize or 
distribute information between different sites/applications that use RDBMSes 
and/or LDAP. Or whatever else...

It is {{B:NOT}} designed as a general-purpose backend that uses RDBMS instead of 
BerkeleyDB (as the standard BDB backend does), though it can be used as such with 
several limitations. Please see {{SECT: LDAP vs RDBMS}} for discussion.

The idea is to use some meta-information to translate LDAP queries to SQL queries, 
leaving relational schema untouched, so that old applications can continue using 
it without any modifications. This allows SQL and LDAP applications to interoperate 
without replication, and exchange data as needed.

The SQL backend is designed to be tunable to virtually any relational schema without 
having to change source (through that meta-information mentioned). Also, it uses 
ODBC to connect to RDBMSes, and is highly configurable for SQL dialects RDBMSes 
may use, so it may be used for integration and distribution of data on different 
RDBMSes, OSes, hosts etc., in other words, in highly heterogeneous environments.

This backend is experimental.

H3: back-sql Configuration

This backend has to be one of the most abused and complex backends there is. 
Therefore, we will go through a simple, small example that comes with the 
OpenLDAP source and can be found in {{F: servers/slapd/back-sql/rdbms_depend/README}}

For this example we will be using PostgreSQL.

First, we add to {{F: /etc/odbc.ini}} a block of the form:

>	[example]                        <===
>	Description         = Example for OpenLDAP's back-sql
>	Driver              = PostgreSQL
>	Trace               = No
>	Database            = example    <===
>	Servername          = localhost
>	UserName            = manager    <===
>	Password            = secret     <===
>	Port                = 5432
>	;Protocol            = 6.4
>	ReadOnly            = No
>	RowVersioning       = No
>	ShowSystemTables    = No
>	ShowOidColumn       = No
>	FakeOidIndex        = No
>	ConnSettings        =

The relevant information for our test setup is highlighted with '<===' on the 
right above.

Next, we add to {{F: /etc/odbcinst.ini}} a block of the form:

>	[PostgreSQL]
>	Description     = ODBC for PostgreSQL
>	Driver          = /usr/lib/libodbcpsql.so
>	Setup           = /usr/lib/libodbcpsqlS.so
>	FileUsage       = 1


We will presume you know how to create a database and user in PostgreSQL and 
how to set a password. Also, we'll presume you can populate the 'example'
database you've just created with the following files, as found in {{F: servers/slapd/back-sql/rdbms_depend/pgsql }} 

>	backsql_create.sql, testdb_create.sql, testdb_data.sql, testdb_metadata.sql

Lastly, run the test:

>	[root@localhost]# cd $SOURCES/tests
>	[root@localhost]# SLAPD_USE_SQL=pgsql ./run sql-test000

Briefly, you should see something like (cut short for space):

>	Cleaning up test run directory leftover from previous run.
>	Running ./scripts/sql-test000-read...
>	running defines.sh
>	Starting slapd on TCP/IP port 9011...
>	Testing SQL backend read operations...
>	Waiting 5 seconds for slapd to start...
>	Testing correct bind... dn:cn=Mitya Kovalev,dc=example,dc=com
>	Testing incorrect bind (should fail)... ldap_bind: Invalid credentials (49)
>	
>	......
>	
>	Filtering original ldif...
>	Comparing filter output...
>	>>>>> Test succeeded

The test is basically readonly; this can be performed by all RDBMSes 
(listed above). 

There is another test, sql-test900-write, which is currently enabled
only for PostgreSQL and IBM db2.

Using {{F: sql-test000}}, files in {{F: servers/slapd/back-sql/rdbms_depend/pgsql/}}
and the man page, you should be set.

Note: This backend is experimental.

H3: Further Information

{{slapd-sql}}(5) and {{F: servers/slapd/back-sql/rdbms_depend/README}}
