Section (5) slapd-relay
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.
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;
directive is allowed by the
- 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.
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.
directive suffices if only naming context rewriting is
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.
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 one 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
statement, to map all the virtual to real naming context data
flow, but none of the real to virtual.
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
are in the real naming
the targets (the
<what> clause) are in
real and in the
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
pseudo-attribute and to the other attribute values of the
entries returned by the
search operation is honored,
which is performed by the frontend.