.TH SLAPD-RELAY 5 "RELEASEDATE" "OpenLDAP LDVERSION"
+.\" Copyright 1998-2011 The OpenLDAP Foundation All Rights Reserved.
+.\" Copying restrictions apply. See COPYRIGHT/LICENSE.
+.\" $OpenLDAP$
.SH NAME
-slapd-relay \- relay backend to slapd
+slapd\-relay \- relay backend to slapd
.SH SYNOPSIS
ETCDIR/slapd.conf
.SH DESCRIPTION
instance into a virtual naming context, with attributeType
and objectClass manipulation, if required.
It requires the
-.B rwm
-.BR overlay .
+.BR slapo\-rwm (5)
+overlay.
.LP
This backend and the above mentioned overlay are experimental.
.SH CONFIGURATION
-These
+The following
.B slapd.conf
-options apply to the relay backend database.
+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
.BR slapd.conf (5)
-manual page.
+manual page; only the
+.B suffix
+directive is allowed by the
+.I relay
+backend.
.TP
-.B relay <real naming context> [massage]
+.B relay <real naming context>
The naming context of the database that is presented
under a virtual naming context.
-The presence of the directive implies that one single database
+The presence of this directive implies that one specific database,
+i.e. the one serving the
+.BR "real naming context" ,
will be presented under a virtual naming context.
-This directive automatically instantiates the
-.B rwm
-.BR overlay .
-If the optional
-.B massage
-keyword is present, the suffix massaging is automatically
-configured as well.
+
+.SH MASSAGING
+The
+.B relay
+database does not automatically rewrite the naming context
+of requests and responses.
+For this purpose, the
+.BR slapo\-rwm (5)
+overlay must be explicitly instantiated, and configured
+as appropriate.
+Usually, the
+.B rwm\-suffixmassage
+directive suffices if only naming context rewriting is required.
+
+.SH ACCESS RULES
+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
+.B 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
+.B relay
+database must refer to identities in the real naming context.
+Examples are reported in the EXAMPLES section.
.SH SCENARIOS
.LP
If no
.B relay
directive is given, the
-.B relay
+.I 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 and so.
+database, and searches to another, or different target databases
+can be selected based on the DN of the request, and so.
.LP
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.
.LP
-.SH Caveats
-The
-.B rwm overlay
-is far from complete.
-.LP
.SH EXAMPLES
To implement a plain virtual naming context mapping
that refers to a single database, use
.LP
.nf
- database relay
- suffix "dc=virtual,dc=naming,dc=context"
- relay "dc=real,dc=naming,dc=context" massage
+ 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"
.fi
.LP
To implement a plain virtual naming context mapping
that looks up the real naming context for each operation, use
.LP
.nf
- database relay
- suffix "dc=virtual,dc=naming,dc=context"
- overlay rwm
- suffixmassage "dc=virtual,dc=naming,dc=context"
- "dc=real,dc=naming,dc=context"
+ database relay
+ suffix "dc=virtual,dc=naming,dc=context"
+ overlay rwm
+ rwm\-suffixmassage "dc=real,dc=naming,dc=context"
.fi
.LP
+This is useful, for instance, to relay different databases that
+share the terminal portion of the naming context (the one that
+is rewritten).
+.LP
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
.LP
.nf
- database relay
- suffix "dc=virtual,dc=naming,dc=context"
- relay "dc=real,dc=naming,dc=context"
- rewriteEngine on
- rewriteContext default
- rewriteRule "dc=virtual,dc=naming,dc=context"
- "dc=real,dc=naming,dc=context" ":"
- rewriteRule searchFilter
- rewriteRule searchResult
- rewriteRule searchResultAttrDN
- rewriteRule matchedDN
+ 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
.fi
.LP
-Note that the virtual database is bound to a single real database,
-so the
-.B rwm overlay
-is automatically instantiated, but the rewrite rules
-are written explicitly to map all the virtual to real
-naming context data flow, but none of the real to virtual.
+Note that the
+.BR slapo\-rwm (5)
+overlay is instantiated, but the rewrite rules are written explicitly,
+rather than automatically as with the
+.B rwm\-suffixmassage
+statement, to map all the virtual to real naming context data flow,
+but none of the real to virtual.
+.LP
+Access rules:
+.LP
+.nf
+ 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
+.fi
+.LP
+Note that, in both databases, the identities (the
+.B <who>
+clause) are in the
+.BR "real naming context" ,
+i.e.
+.BR "`dc=example,dc=com'" ,
+while the targets (the
+.B <what>
+clause) are in the
+.B real
+and in the
+.BR "virtual naming context" ,
+respectively.
+.SH ACCESS CONTROL
+The
+.B relay
+backend does not honor any of the access control semantics described in
+.BR slapd.access (5);
+all access control is delegated to the relayed database(s).
+Only
+.B read (=r)
+access to the
+.B entry
+pseudo-attribute and to the other attribute values of the entries
+returned by the
+.B search
+operation is honored, which is performed by the frontend.
.SH FILES
.TP
ETCDIR/slapd.conf
default slapd configuration file
.SH SEE ALSO
.BR slapd.conf (5),
+.BR slapd\-config (5),
+.BR slapo\-rwm (5),
.BR slapd (8).
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