Provided by: slapd_2.4.42+dfsg-2ubuntu3.13_amd64 bug


       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)

       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


       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).