2 Description of the virtual host mechanism in &yaz; GFS
3 Included in both manual and man page for yaz-ztest
7 The Virtual hosts mechanism allows a &yaz; frontend server to
8 support multiple backends. A backend is selected on the basis of
9 the TCP/IP binding (port+listening adddress) and/or the virtual host.
12 A backend can be configured to execute in a particular working
13 directory. Or the &yaz; frontend may perform <ulink url="&url.cql;">&acro.cql;</ulink> to &acro.rpn; conversion, thus
14 allowing traditional &acro.z3950; backends to be offered as a
15 <ulink url="&url.sru;">&acro.sru;</ulink> service.
16 &acro.sru; Explain information for a particular backend may also be specified.
19 For the HTTP protocol, the virtual host is specified in the Host header.
20 For the &acro.z3950; protocol, the virtual host is specified as in the
21 Initialize Request in the OtherInfo, OID 1.2.840.10003.10.1000.81.1.
25 Not all &acro.z3950; clients allows the VHOST information to be set.
26 For those the selection of the backend must rely on the
27 TCP/IP information alone (port and address).
31 The &yaz; frontend server uses &acro.xml; to describe the backend
32 configurations. Command-line option <literal>-f</literal>
33 specifies filename of the &acro.xml; configuration.
36 The configuration uses the root element <literal>yazgfs</literal>.
37 This element includes a list of <literal>listen</literal> elements,
38 followed by one or more <literal>server</literal> elements.
41 The <literal>listen</literal> describes listener (transport end point),
42 such as TCP/IP, Unix file socket or SSL server. Content for
45 <varlistentry><term>CDATA (required)</term>
48 The CDATA for the <literal>listen</literal> element holds the
49 listener string, such as <literal>tcp:@:210</literal>,
50 <literal>tcp:server1:2100</literal>,
55 <varlistentry><term>attribute <literal>id</literal> (optional)</term>
58 identifier for this listener. This may be referred to from
66 We expect more information to be added for the listen section in
67 a future version, such as CERT file for SSL servers.
72 The <literal>server</literal> describes a server and the parameters
73 for this server type. Content for a server:
75 <varlistentry><term>attribute <literal>id</literal> (optional)</term>
78 Identifier for this server. Currently not used for anything,
79 but it might be for logging purposes.
84 <varlistentry><term>attribute <literal>listenref</literal> (optional)</term>
87 Specifies listener for this server. If this attribute is not
88 given, the server is accessible from all listener. In order
89 for the server to be used for real, howeever, the virtual host
90 must match (if specified in the configuration).
95 <varlistentry><term>element <literal>config</literal> (optional)</term>
98 Specifies the server configuration. This is equivalent
99 to the config specified using command line option
100 <literal>-c</literal>.
105 <varlistentry><term>element <literal>directory</literal> (optional)</term>
108 Specifies a working directory for this backend server. If
109 specifid, the &yaz; fronend changes current working directory
110 to this directory whenever a backend of this type is
111 started (backend handler bend_start), stopped (backend handler hand_stop)
112 and initialized (bend_init).
117 <varlistentry><term>element <literal>host</literal> (optional)</term>
120 Specifies the virtual host for this server. If this is specified
121 a client <emphasis>must</emphasis> specify this host string in
122 order to use this backend.
127 <varlistentry><term>element <literal>cql2rpn</literal> (optional)</term>
130 Specifies a filename that includes <ulink url="&url.cql;">&acro.cql;</ulink> to &acro.rpn; conversion for this
131 backend server. See <ulink url="&url.cql;">&acro.cql;</ulink> section in &yaz; manual.
132 If given, the backend server will only "see" a Type-1/&acro.rpn; query.
137 <varlistentry><term>element <literal>explain</literal> (optional)</term>
140 Specifies <ulink url="&url.sru;">&acro.sru;</ulink> ZeeRex content for this
141 server - copied verbatim to the client.
142 As things are now, some of the Explain content seems redundant
143 because host information, etc. is also stored elsewhere.
146 The format of the Explain record is described in detail, with
147 examples, on the file at the
148 <ulink url="&url.zeerex.explain;">ZeeRex</ulink> web-site.
156 The &acro.xml; below configures a server that accepts connections from
157 two ports, TCP/IP port 9900 and a local UNIX file socket.
158 We name the TCP/IP server <literal>public</literal> and the
159 other server <literal>internal</literal>.
164 <listen id="public">tcp:@:9900</listen>
165 <listen id="internal">unix:/var/tmp/socket</listen>
166 <server id="server1">
167 <host>server1.mydomain</host>
168 <directory>/var/www/s1</directory>
169 <config>config.cfg</config>
171 <server id="server2">
172 <host>server2.mydomain</host>
173 <directory>/var/www/s2</directory>
174 <config>config.cfg</config>
175 <cql2rpn>../etc/pqf.properties</cql2rpn>
176 <explain xmlns="http://explain.z3950.org/dtd/2.0/">
178 <host>server2.mydomain</host>
180 <database>a</database>
184 <server id="server3" listenref="internal">
185 <directory>/var/www/s3</directory>
186 <config>config.cfg</config>
192 There are three configured backend servers. The first two
193 servers, <literal>"server1"</literal> and <literal>"server2"</literal>,
194 can be reached by both listener addresses - since
195 no <literal>listenref</literal> attribute is specified.
196 In order to distinguish between the two a virtual host has
197 been specified for each of server in the <literal>host</literal>
201 For <literal>"server2"</literal> elements for
202 <ulink url="&url.cql;">&acro.cql;</ulink> to &acro.rpn; conversion
203 is supported and explain information has been added (a short one here
204 to keep the example small).
207 The third server, <literal>"server3"</literal> can only be reached
208 via listener <literal>"internal"</literal>.
211 <!-- Keep this comment at the end of the file
216 sgml-minimize-attributes:nil
217 sgml-always-quote-attributes:t
220 sgml-parent-document: "zebrasrv.xml"
221 sgml-local-catalogs: nil
222 sgml-namecase-general:t