Langue: en

Version: 2009/02/24 (ubuntu - 08/07/09)

Section: 5 (Format de fichier)


slapd-relay - relay backend to slapd




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 slapo-rwm(5) overlay.

This backend and the above mentioned overlay are experimental.


The following slapd.conf directives apply to the relay backend database. That is, they must follow a "database relay" line and come before any subsequent "backend" or "database" lines. Other database options are described in the slapd.conf(5) manual page; only the suffix directive is allowed by the relay backend.
relay <real naming context>
The naming context of the database that is presented under a virtual naming context. The presence of this directive implies that one specific database, i.e. the one serving the real naming context, will be presented under a virtual naming context.


The relay database does not automatically rewrite the naming context of requests and responses. For this purpose, the slapo-rwm(5) overlay must be explicitly instantiated, and configured as appropriate. Usually, the rwm-suffixmassage directive suffices if only naming context rewriting is required.


One important issue is that access rules are based on the identity that issued the operation. After massaging from the virtual to the real naming context, the frontend sees the operation as performed by the identity in the real naming context. Moreover, since back-relay bypasses the real database frontend operations by short-circuiting operations through the internal backend API, the original database access rules do not apply but in selected cases, i.e. when the backend itself applies access control. As a consequence, the instances of the relay database must provide own access rules that are consistent with those of the original database, possibly adding further specific restrictions. So, access rules in the relay database must refer to identities in the real naming context. Examples are reported in the EXAMPLES section.


If no relay directive is given, the relay database does not refer to any specific database, but the most appropriate one is looked-up after rewriting the request DN for the operation that is being handled.

This allows to write carefully crafted rewrite rules that cause some of the requests to be directed to one database, and some to another; e.g., authentication can be mapped to one database, and searches to another, or different target databases can be selected based on the DN of the request, and so.

Another possibility is to map the same operation to different databases based on details of the virtual naming context, e.g. groups on one database and persons on another.


To implement a plain virtual naming context mapping that refers to a single database, use
   database                relay
   suffix                  "dc=virtual,dc=naming,dc=context"
   relay                   "dc=real,dc=naming,dc=context"
   overlay                 rwm
   rwm-suffixmassage       "dc=real,dc=naming,dc=context"

To implement a plain virtual naming context mapping that looks up the real naming context for each operation, use

   database                relay
   suffix                  "dc=virtual,dc=naming,dc=context"
   overlay                 rwm
   rwm-suffixmassage       "dc=real,dc=naming,dc=context"

This is useful, for instance, to relay different databases that share the terminal portion of the naming context (the one that is rewritten).

To implement the old-fashioned suffixalias, e.g. mapping the virtual to the real naming context, but not the results back from the real to the virtual naming context, use

   database                relay
   suffix                  "dc=virtual,dc=naming,dc=context"
   relay                   "dc=real,dc=naming,dc=context"
   overlay                 rwm
   rwm-rewriteEngine       on
   rwm-rewriteContext      default
   rwm-rewriteRule         "dc=virtual,dc=naming,dc=context"
                           "dc=real,dc=naming,dc=context" ":@"
   rwm-rewriteContext      searchFilter
   rwm-rewriteContext      searchEntryDN
   rwm-rewriteContext      searchAttrDN
   rwm-rewriteContext      matchedDN

Note that the slapo-rwm(5) overlay is instantiated, but the rewrite rules are written explicitly, rather than automatically as with the rwm-suffixmassage statement, to map all the virtual to real naming context data flow, but none of the real to virtual.

Access rules:

   database                bdb
   suffix                  "dc=example,dc=com"
   # skip...
   access to dn.subtree="dc=example,dc=com"
           by dn.exact="cn=Supervisor,dc=example,dc=com" write
           by * read
   database                relay
   suffix                  "o=Example,c=US"
   relay                   "dc=example,dc=com"
   overlay                 rwm
   rwm-suffixmassage       "dc=example,dc=com"
   # skip ...
   access to dn.subtree="o=Example,c=US"
           by dn.exact="cn=Supervisor,dc=example,dc=com" write
           by dn.exact="cn=Relay Supervisor,dc=example,dc=com" write
           by * read

Note that, in both databases, the identities (the <who> clause) are in the real naming context, i.e. `dc=example,dc=com', while the targets (the <what> clause) are in the real and in the virtual naming context, respectively.


The relay backend does not honor any of the access control semantics described in slapd.access(5); all access control is delegated to the relayed database(s). Only read (=r) access to the entry pseudo-attribute and to the other attribute values of the entries returned by the search operation is honored, which is performed by the frontend.


default slapd configuration file


slapd.conf(5), slapd-config(5), slapo-rwm(5), slapd(8).