2 $Id: gfs-virtual.xml,v 1.3 2005-08-05 09:36:15 adam Exp $
3 Description of the virtual host mechanism in YAZ GFS
4 Included in both manual and man page for yaz-ztest
8 The Virtual hosts mechanism allows a YAZ frontend server to
9 support multiple backends. A backend is selected on the basis of
10 the TCP/IP binding (port+listening adddress) and/or the virtual host.
13 A backend can be configured to execute in a particular working
14 directory. Or the YAZ frontend may perform CQL to RPN conversion, thus
15 allowing traditional Z39.50 backends to be offered as a SRW/SRU
16 service. SRW/SRU Explain information for a particular backend may also
20 For the HTTP protocol, the virtual host is specified in the Host header.
21 For the Z39.50 protocol, the virtual host is specified as in the
22 Initialize Request in the OtherInfo, OID 1.2.840.10003.10.1000.81.1.
26 Not all Z39.50 clients allows the VHOST information to be set.
27 For those the selection of the backend must rely on the
28 TCP/IP information alone (port and address).
32 The YAZ frontend server uses XML to describe the backend
33 configurations. Command-line option <literal>-f</literal>
34 specifies filename of the XML configuration.
37 The configuration uses the root element <literal>yazgfs</literal>.
38 This element includes a list of <literal>listen</literal> elements,
39 followed by one or more <literal>server</literal> elements.
42 The <literal>listen</literal> describes listener (transport end point),
43 such as TCP/IP, Unix file socket or SSL server. Content for
46 <varlistentry><term>CDATA (required)</term>
49 The CDATA for the <literal>listen</literal> element holds the
50 listener string, such as <literal>tcp:@:210</literal>,
51 <literal>tcp:server1:2100</literal>,
56 <varlistentry><term>attribute <literal>id</literal> (optional)</term>
59 identifier for this listener. This may be referred to from
67 We expect more information to be added for the listen section in
68 a future version, such as CERT file for SSL servers.
73 The <literal>server</literal> describes a server and the parameters
74 for this server type. Content for a server:
76 <varlistentry><term>attribute <literal>id</literal> (optional)</term>
79 Identifier for this server. Currently not used for anything,
80 but it might be for logging purposes.
85 <varlistentry><term>attribute <literal>listenref</literal> (optional)</term>
88 Specifies listener for this server. If this attribute is not
89 given, the server is accessible from all listener. In order
90 for the server to be used for real, howeever, the virtual host
91 must match (if specified in the configuration).
96 <varlistentry><term>element <literal>config</literal> (optional)</term>
99 Specifies the server configuration. This is equivalent
100 to the config specified using command line option
101 <literal>-c</literal>.
106 <varlistentry><term>element <literal>directory</literal> (optional)</term>
109 Specifies a working directory for this backend server. If
110 specifid, the YAZ fronend changes current working directory
111 to this directory whenever a backend of this type is
112 started (backend handler bend_start), stopped (backend handler hand_stop)
113 and initialized (bend_init).
118 <varlistentry><term>element <literal>host</literal> (optional)</term>
121 Specifies the virtual host for this server. If this is specified
122 a client <emphasis>must</emphasis> specify this host string in
123 order to use this backend.
128 <varlistentry><term>element <literal>cql2rpn</literal> (optional)</term>
131 Specifies a filename that includes CQL to RPN conversion for this
132 backend server. See &reference-tools-cql-map;
133 If given, the backend server will only "see" a Type-1/RPN query.
138 <varlistentry><term>element <literal>explain</literal> (optional)</term>
141 Specifies SRW/SRU ZeeRex content for this server. Copied verbatim
142 to the client. As things are now, some of the Explain content
143 seeem redundant because host information, etc. is also stored
152 The XML below configures a server that accepts connections from
153 two ports, TCP/IP port 9900 and a local UNIX file socket.
154 We name the TCP/IP server <literal>public</literal> and the
155 other server <literal>internal</literal>.
160 <listen id="public">tcp:@:9900</listen>
161 <listen id="internal">unix:/var/tmp/socket</listen>
162 <server id="server1">
163 <host>server1.mydomain</host>
164 <directory>/var/www/s1</directory>
165 <config>config.cfg</config>
167 <server id="server2">
168 <host>server2.mydomain</host>
169 <directory>/var/www/s2</directory>
170 <config>config.cfg</config>
171 <cql2rpn>../etc/pqf.properties</cql2rpn>
172 <explain xmlns="http://explain.z3950.org/dtd/2.0/">
174 <host>server2.mydomain</host>
176 <database>a</database>
180 <server id="server3" listenref="internal">
181 <directory>/var/www/s3</directory>
182 <config>config.cfg</config>
188 There are three configured backend servers. The first two
189 servers, <literal>"server1"</literal> and <literal>"server2"</literal>,
190 can be reached by both listener addresses - since
191 no <literal>listenref</literal> attribute is specified.
192 In order to distinguish between the two a virtual host has
193 been specified for each of server in the <literal>host</literal>
197 For <literal>"server2"</literal> elements for CQL to RPN conversion
198 is supported and explain information has been added (a short one here
199 to keep the example small).
202 The third server, <literal>"server3"</literal> can only be reached
203 via listener <literal>"internal"</literal>.
206 <!-- Keep this comment at the end of the file
211 sgml-minimize-attributes:nil
212 sgml-always-quote-attributes:t
215 sgml-parent-document: "yaz.xml"
216 sgml-local-catalogs: nil
217 sgml-namecase-general:t