.TH SLAPD-ASYNCMETA 5 "RELEASEDATE" "OpenLDAP LDVERSION"
.\" Copyright 2016-2021 The OpenLDAP Foundation.
.\" Portions Copyright 2016 Symas Corporation.
.\" Copying restrictions apply.  See the COPYRIGHT file.
.\" $OpenLDAP$
.\"

.SH NAME
slapd\-asyncmeta \- asynchronous metadirectory backend to slapd
.SH SYNOPSIS
ETCDIR/slapd.conf
.SH DESCRIPTION
The
.B asyncmeta
backend to
.BR 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 (DIT).

.LP
A good knowledge of the functionality of the
.BR slapd\-meta(5)
backend  is recommended.   This  backend has been designed as
an asynchronous version of the
.B meta
backend. Unlike
.B meta
, the operation handling threads are no longer pending
on the response from the remote server, thus decreasing the
number of threads necessary to handle the same load. While
.B asyncmeta
maintains the functionality of
.B meta
and has a largely similar codebase,
some changes in operation and some new configuration directives have been
added. Some configuration options, such as
.B conn\-pool\-max ,
.B conn\-ttl ,
.B single\-conn ,
and
.B use\-temporary\-conn
have been removed, as they are no longer relevant.
.LP
.B New connection handling:
.LP

Unlike
.B meta,
which caches bound connections, the
.B asyncmeta
works with a configured maximum number of connections per target.
For each request redirected to a target, a different connection is selected.
Each connection has a queue, to which the request is added before it is sent to the
remote server, and is removed after the last response for that request is received.
 For each new request, the connection with the smallest number of pending requests
is selected, or using round\-robin if the numbers are equal.
.LP
.B Overlays:
.LP
Due to implementation specifics, there is no guarantee that any of the existing OpenLDAP overlays will work with
.B asyncmeta
backend.

.SH EXAMPLES
Refer to
.B slapd\-meta(5)
for configuration examples.

.SH CONFIGURATION
These
.B slapd.conf
options apply to the ASYNCMETA backend database.
That is, they must follow a "database asyncmeta" line and come before any
subsequent "backend" or "database" lines.
Other database options are described in the
.BR slapd.conf (5)
manual page.

.SH SPECIAL CONFIGURATION DIRECTIVES
Target configuration starts with the "uri" directive.
All the configuration directives that are not specific to targets
should be defined first for clarity, including those that are common
to all backends.
They are:

.TP
.B default\-target none
This directive forces the backend to reject all those operations
that must resolve to a single target in case none or multiple
targets are selected.
They include: add, delete, modify, modrdn; compare is not included, as
well as bind since, as they don't alter entries, in case of multiple
matches an attempt is made to perform the operation on any candidate
target, with the constraint that at most one must succeed.
This directive can also be used when processing targets to mark a
specific target as default.

.TP
.B dncache\-ttl {DISABLED|forever|<ttl>}
This directive sets the time-to-live of the DN cache.
This caches the target that holds a given DN to speed up target
selection in case multiple targets would result from an uncached
search; forever means cache never expires; disabled means no DN
caching; otherwise a valid ( > 0 ) ttl is required, in the format
illustrated for the
.B idle\-timeout
directive.

.TP
.B onerr {CONTINUE|report|stop}
This directive allows one to select the behavior in case an error is returned
by one target during a search.
The default, \fBcontinue\fP, consists in continuing the operation,
trying to return as much data as possible.
If the value is set to \fBstop\fP, the search is terminated as soon
as an error is returned by one target, and the error is immediately
propagated to the client.
If the value is set to \fBreport\fP, the search is continued to the end
but, in case at least one target returned an error code, the first
non-success error code is returned.

.TP
.B max\-timeout\-ops <number>
Specify the number of consecutive timed out requests,
after which the connection will be considered faulty and dropped.

.TP
.B max\-pending\-ops <number>
The maximum number of pending requests stored in a connection's queue.
The default is 128. When this number is exceeded,
.B LDAP_BUSY
will be returned to the client.

.TP
.B max\-target\-conns <number>
The maximum number of connections per target. Unlike
.B slapd\-meta(5),
no new connections will be created
once this number is reached. The default value is 255.

.TP
.B norefs <NO|yes>
If
.BR yes ,
do not return search reference responses.
By default, they are returned unless request is LDAPv2.
If set before any target specification, it affects all targets, unless
overridden by any per-target directive.

.TP
.B noundeffilter <NO|yes>
If
.BR yes ,
return success instead of searching if a filter is undefined or contains
undefined portions.
By default, the search is propagated after replacing undefined portions
with
.BR (!(objectClass=*)) ,
which corresponds to the empty result set.
If set before any target specification, it affects all targets, unless
overridden by any per-target directive.

.TP
.B protocol\-version {0,2,3}
This directive indicates what protocol version must be used to contact
the remote server.
If set to 0 (the default), the proxy uses the same protocol version
used by the client, otherwise the requested protocol is used.
The proxy returns \fIunwillingToPerform\fP if an operation that is
incompatible with the requested protocol is attempted.
If set before any target specification, it affects all targets, unless
overridden by any per-target directive.

.TP
.B pseudoroot\-bind\-defer {YES|no}
This directive, when set to
.BR yes ,
causes the authentication to the remote servers with the pseudo-root
identity (the identity defined in each
.B idassert-bind
directive) to be deferred until actually needed by subsequent operations.
Otherwise, all binds as the rootdn are propagated to the targets.

.TP
.B quarantine <interval>,<num>[;<interval>,<num>[...]]
Turns on quarantine of URIs that returned
.IR LDAP_UNAVAILABLE ,
so that an attempt to reconnect only occurs at given intervals instead
of any time a client requests an operation.
The pattern is: retry only after at least
.I interval
seconds elapsed since last attempt, for exactly
.I num
times; then use the next pattern.
If
.I num
for the last pattern is "\fB+\fP", it retries forever; otherwise,
no more retries occur.
This directive must appear before any target specification;
it affects all targets with the same pattern.

.TP
.B rebind\-as\-user {NO|yes}
If this option is given, the client's bind credentials are remembered
for rebinds, when trying to re-establish a broken connection,
or when chasing a referral, if
.B chase\-referrals
is set to
.IR yes .

.TP
.B session\-tracking\-request {NO|yes}
Adds session tracking control for all requests.
The client's IP and hostname, and the identity associated to each request,
if known, are sent to the remote server for informational purposes.
This directive is incompatible with setting \fIprotocol\-version\fP to 2.
If set before any target specification, it affects all targets, unless
overridden by any per-target directive.

.SH TARGET SPECIFICATION
Target specification starts with a "uri" directive:

.TP
.B uri <protocol>://[<host>]/<naming context> [...]
Identical to
.B meta.
See
.B slapd\-meta(5)
for details.

.TP
.B acl\-authcDN "<administrative DN for access control purposes>"
DN which is used to query the target server for acl checking,
as in the LDAP backend; it is supposed to have read access
on the target server to attributes used on the proxy for acl checking.
There is no risk of giving away such values; they are only used to
check permissions.
.B The acl\-authcDN identity is by no means implicitly used by the proxy
.B when the client connects anonymously.

.TP
.B acl\-passwd <password>
Password used with the
.B acl\-authcDN
above.

.TP
.B bind\-timeout <microseconds>
This directive defines the timeout, in microseconds, used when polling
for response after an asynchronous bind connection. See
.B slapd\-meta(5)
for details.

.TP
.B chase\-referrals {YES|no}
enable/disable automatic referral chasing, which is delegated to the
underlying libldap, with rebinding eventually performed if the
\fBrebind\-as\-user\fP directive is used.  The default is to chase referrals.
If set before any target specification, it affects all targets, unless
overridden by any per-target directive.

.TP
.B client\-pr {accept-unsolicited|DISABLE|<size>}
This feature allows one to use RFC 2696 Paged Results control when performing
search operations with a specific target,
irrespective of the client's request. See
.B slapd\-meta(5)
for details.

.TP
.B default\-target [<target>]
The "default\-target" directive can also be used during target specification.
With no arguments it marks the current target as the default.
The optional number marks target <target> as the default one, starting
from 1.
Target <target> must be defined.

.TP
.B filter <pattern>
This directive allows specifying a
.BR regex (5)
pattern to indicate what search filter terms are actually served by a target.

In a search request, if the search filter matches the \fIpattern\fP
the target is considered while fulfilling the request; otherwise
the target is ignored. There may be multiple occurrences of
the
.B filter
directive for each target.

.TP
.B idassert\-authzFrom <authz-regexp>
if defined, selects what
.I local
identities are authorized to exploit the identity assertion feature.
The string
.B <authz-regexp>
follows the rules defined for the
.I authzFrom
attribute.
See
.BR slapd.conf (5),
section related to
.BR authz\-policy ,
for details on the syntax of this field.

.HP
.hy 0
.B idassert\-bind
.B bindmethod=none|simple|sasl [binddn=<simple DN>] [credentials=<simple password>]
.B [saslmech=<SASL mech>] [secprops=<properties>] [realm=<realm>]
.B [authcId=<authentication ID>] [authzId=<authorization ID>]
.B [authz={native|proxyauthz}] [mode=<mode>] [flags=<flags>]
.B [starttls=no|yes|critical]
.B [tls_cert=<file>]
.B [tls_key=<file>]
.B [tls_cacert=<file>]
.B [tls_cacertdir=<path>]
.B [tls_reqcert=never|allow|try|demand]
.B [tls_reqsan=never|allow|try|demand]
.B [tls_cipher_suite=<ciphers>]
.B [tls_ecname=<names>]
.B [tls_protocol_min=<major>[.<minor>]]
.B [tls_crlcheck=none|peer|all]
Allows one to define the parameters of the authentication method that is
internally used by the proxy to authorize connections that are
authenticated by other databases. See
.B slapd\-meta(5)
for details.

.TP
.B idle\-timeout <time>
This directive causes a a persistent connection  to  be  dropped after
it  has been idle for the specified time. The connection will be re-created
the next time it is selected for use. A connection is considered idle if no
attempts have been made by the backend to use it to send a request to
the backend server. If there are still pending requests in
its queue, the connection will be dropped after the last
request one has either received a result or has timed out.

[<d>d][<h>h][<m>m][<s>[s]]

where <d>, <h>, <m> and <s> are respectively treated as days, hours,
minutes and seconds.
If set before any target specification, it affects all targets, unless
overridden by any per-target directive.

.TP
.B keepalive  <idle>:<probes>:<interval>
The
.B keepalive
parameter sets the values of \fIidle\fP, \fIprobes\fP, and \fIinterval\fP
used to check whether a socket is alive;
.I idle
is the number of seconds a connection needs to remain idle before TCP
starts sending keepalive probes;
.I probes
is the maximum number of keepalive probes TCP should send before dropping
the connection;
.I interval
is interval in seconds between individual keepalive probes.
Only some systems support the customization of these values;
the
.B keepalive
parameter is ignored otherwise, and system-wide settings are used.

.TP
.B tcp\-user\-timeout  <milliseconds>
If non-zero, corresponds to the
.B TCP_USER_TIMEOUT
set on the target connections, overriding the operating system setting.
Only some systems support the customization of this parameter, it is
ignored otherwise and system-wide settings are used.

.TP
.B map "{attribute|objectclass} [<local name>|*] {<foreign name>|*}"
This maps object classes and attributes as in the LDAP backend.
See
.BR slapd\-ldap (5).

.TP
.B network\-timeout <time>
Sets the network timeout value after which
.BR poll (2)/ select (2)
following a
.BR connect (2)
returns in case of no activity while sending an operation to the remote target.
The value is in milliseconds, and it can be specified as for
.BR idle\-timeout .
If set before any target specification, it affects all targets, unless
overridden by any per-target directive.

.TP
.B nretries {forever|never|<nretries>}
This directive defines how many times forwarding an operation should be retried
in case of temporary failure in contacting a target. The number of retries
is per operation, so if a bind to the target is necessary first, the remaining
number is decremented. If defined
before any target specification, it applies to all targets (by default,
.BR 3
times);
the global value can be overridden by redefinitions inside each target
specification.

.TP
.B rewrite* ...
The rewrite options are identical to the
.B meta
backend. See the
.B REWRITING
section of
.B slapd\-meta(5).

.TP
.B subtree\-{exclude|include} "<rule>"
This directive allows one to indicate what subtrees are actually served
by a target. See
.B slapd\-meta(5)
for details.

.TP
.B suffixmassage "<local suffix>" "<remote suffix>"
.B slapd\-asyncmeta
does not support the rewrite engine used by
the LDAP and META backends.
.B suffixmassage
can be used to perform DN suffix rewriting, the same way as the obsoleted suffixmassage directive
previously used by the LDAP backend.

.TP
.B t\-f\-support {NO|yes|discover}
enable if the remote server supports absolute filters
(see \fIRFC 4526\fP for details).
If set to
.BR discover ,
support is detected by reading the remote server's root DSE.
If set before any target specification, it affects all targets, unless
overridden by any per-target directive.

.TP
.B timeout [<op>=]<val> [...]
This directive allows one to set per-operation timeouts.
Operations can be

\fB<op> ::= bind, add, delete, modrdn, modify, compare, search\fP

By default, the timeout for all operations is 2 seconds.

See
.B slapd\-meta(5)
for details.

.TP
.B tls {none|[try\-]start|[try\-]propagate|ldaps}
B [starttls=no]
.B [tls_cert=<file>]
.B [tls_key=<file>]
.B [tls_cacert=<file>]
.B [tls_cacertdir=<path>]
.B [tls_reqcert=never|allow|try|demand]
.B [tls_reqsan=never|allow|try|demand]
.B [tls_cipher_suite=<ciphers>]
.B [tls_ecname=<names>]
.B [tls_crlcheck=none|peer|all]
.RS
Specify TLS settings regular connections.

If the first parameter is not "none" then this configures the TLS
settings to be used for regular connections.
The StartTLS extended operation will be used when establishing the
connection unless the URI directive protocol scheme is \fBldaps://\fP.
In that case this keyword may only be set to "ldaps" and the StartTLS
operation will not be used.

\fBpropagate\fP issues the StartTLS operation only if the original
connection did.
The \fBtry\-\fP prefix instructs the proxy to continue operations
if the StartTLS operation failed; its use is highly deprecated.
The TLS settings default to the same as the main slapd TLS settings,
except for
.B tls_reqcert
which defaults to "demand",
.B tls_reqsan
which defaults to "allow", and
.B starttls
which is overshadowed by the first keyword and thus ignored.

If set before any target specification, it affects all targets, unless
overridden by any per-target directive.
.RE

.SH SCENARIOS
See
.B slapd\-meta(5)
for configuration scenarios.

.SH ACLs
ACL behavior is identical to meta. See
.B slapd\-meta(5).

.SH ACCESS CONTROL
The
.B asyncmeta
backend does not honor all ACL semantics as described in
.BR slapd.access (5).
In general, access checking is delegated to the remote server(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\-ldap (5),
.BR slapd\-meta (5),
.BR slapo\-pcache (5),
.BR slapd (8),
.BR regex (7),
.BR re_format (7).
.SH AUTHOR
Nadezhda Ivanova, based on back-meta by Pierangelo Masarati.