<?xml version="1.0"?>
<!DOCTYPE document [
  <!ENTITY project SYSTEM "project.xml">
]>
<document url="host.html">

  &project;

  <properties>
    <author email="craigmcc@apache.org">Craig R. McClanahan</author>
    <author email="remm@apache.org">Remy Maucherat</author>
    <author email="yoavs@apache.org">Yoav Shapira</author>
    <title>The Host Container</title>
  </properties>

<body>


<section name="Introduction">

  <p>The <strong>Host</strong> element represents a <em>virtual host</em>,
  which is an association of a network name for a server (such as
  "www.mycompany.com" with the particular server on which Catalina is
  running.  In order to be effective, this name must be registered in the
  <em>Domain Name Service</em> (DNS) server that manages the Internet
  domain you belong to - contact your Network Administrator for more
  information.</p>

  <p>In many cases, System Administrators wish to associate more than
  one network name (such as <code>www.mycompany.com</code> and
  <code>company.com</code>) with the same virtual host and applications.
  This can be accomplished using the <a href="#Host Name Aliases">Host
  Name Aliases</a> feature discussed below.</p>

  <p>One or more <strong>Host</strong> elements are nested inside an
  <a href="engine.html">Engine</a> element.  Inside the Host element, you
  can nest <a href="context.html">Context</a> elements for the web
  applications associated with this virtual host.  Exactly one of the Hosts
  associated with each Engine MUST have a name matching the
  <code>defaultHost</code> attribute of that Engine.</p>

    <blockquote><em>
    <p>The description below uses the variable name $CATALINA_HOME
    to refer to the directory into which you have installed Tomcat 6,
    and is the base directory against which most relative paths are
    resolved.  However, if you have configured Tomcat 6 for multiple
    instances by setting a CATALINA_BASE directory, you should use
    $CATALINA_BASE instead of $CATALINA_HOME for each of these
    references.</p>
    </em></blockquote>

</section>


<section name="Attributes">

  <subsection name="Common Attributes">

    <p>All implementations of <strong>Host</strong>
    support the following attributes:</p>

    <attributes>

      <attribute name="appBase" required="true">
        <p>The <em>Application Base</em> directory for this virtual host.
        This is the pathname of a directory that may contain web applications
        to be deployed on this virtual host.  You may specify an
        absolute pathname for this directory, or a pathname that is relative
        to the <code>$CATALINA_BASE</code> directory.  See
        <a href="#Automatic Application Deployment">Automatic Application
        Deployment</a> for more information on automatic recognition and
        deployment of web applications to be deployed automatically.</p>
      </attribute>

      <attribute name="autoDeploy" required="false">
        <p>This flag value indicates if new web applications, dropped in to
        the <code>appBase</code> directory while Tomcat is running, should
        be automatically deployed.  The flag's value defaults to true.  See
        <a href="#Automatic Application Deployment">Automatic Application
        Deployment</a> for more information.</p>
      </attribute>

      <attribute name="backgroundProcessorDelay" required="false">
        <p>This value represents the delay in seconds between the 
        invocation of the backgroundProcess method on this host and 
        its child containers, including all contexts. 
        Child containers will not be invoked if their delay value is not 
        negative (which would mean they are using their own processing 
        thread). Setting this to a positive value will cause 
        a thread to be spawn. After waiting the specified amount of time, 
        the thread will invoke the backgroundProcess method on this host 
        and all its child containers. A host will use background processing to
        perform live web application deployment related tasks. If not 
        specified, the default value for this attribute is -1, which means 
        the host will rely on the background processing thread of its parent 
        engine.</p>
      </attribute>

      <attribute name="className" required="false">
        <p>Java class name of the implementation to use.  This class must
        implement the <code>org.apache.catalina.Host</code> interface.
        If not specified, the standard value (defined below) will be used.</p>
      </attribute>

      <attribute name="deployOnStartup" required="false">
        <p>This flag value indicates if web applications from this host should
        be automatically deployed by the host configurator.
        The flag's value defaults to true.  See
        <a href="#Automatic Application Deployment">Automatic Application
        Deployment</a> for more information.</p>
      </attribute>

      <attribute name="name" required="true">
        <p>Network name of this virtual host, as registered in your
        <em>Domain Name Service</em> server.  One of the Hosts nested within
        an <a href="engine.html">Engine</a> MUST have a name that matches the
        <code>defaultHost</code> setting for that Engine.  See
        <a href="#Host Name Aliases">Host Name Aliases</a> for information
        on how to assign more than one network name to the same
        virtual host.</p>
      </attribute>

    </attributes>

  </subsection>


  <subsection name="Standard Implementation">

    <p>The standard implementation of <strong>Host</strong> is
    <strong>org.apache.catalina.core.StandardHost</strong>.
    It supports the following additional attributes (in addition to the
    common attributes listed above):</p>

    <attributes>

      <attribute name="deployXML" required="false">
        <p>Set to <code>false</code> if you want to disable parsing the context.xml
        file embedded inside the application (located at <code>/META-INF/context.xml</code>). 
        Security consious environments should set this to <code>false</code> to prevent
        applications from interacting with the container's configuration. The 
        administrator will then be responsible for providing an external context 
        configuration file, and put it in 
        <code>$CATALINA_HOME/conf/[enginename]/[hostname]/</code>.
        The flag's value defaults to <code>true</code>.</p>
      </attribute>

      <attribute name="errorReportValveClass" required="false">
        <p>Java class name of the error reporting valve which will be used
        by this Host. The responsability of this valve is to output error
        reports. Setting this property allows to customize the look of the
        error pages which will be generated by Tomcat. This class must
        implement the
        <code>org.apache.catalina.Valve</code> interface. If none is specified,
        the value <code>org.apache.catalina.valves.ErrorReportValve</code>
        will be used by default.</p>
      </attribute>

      <attribute name="unpackWARs" required="false">
        <p>Set to <code>true</code> if you want web applications that are
        placed in the <code>appBase</code> directory as web application
        archive (WAR) files to be unpacked into a corresponding disk directory
        structure, <code>false</code> to run such web applications directly
        from a WAR file.  See
        <a href="#Automatic Application Deployment">Automatic Application
        Deployment</a> for more information.</p>
      </attribute>

      <attribute name="workDir" required="false">
        <p>Pathname to a scratch directory to be used by applications for
        this Host. Each application will have its own sub directory with
        temporary read-write use.  Configuring a Context workDir will override
        use of the Host workDir configuration.  This directory will be made
        visible to servlets in the web application by a servlet context
        attribute (of type <code>java.io.File</code>) named
        <code>javax.servlet.context.tempdir</code> as described in the
        Servlet Specification.  If not specified, a suitable directory
        underneath <code>$CATALINA_HOME/work</code> will be provided.</p>
      </attribute>

    </attributes>

  </subsection>


</section>


<section name="Nested Components">

  <p>You can nest one or more <a href="context.html">Context</a> elements
  inside this <strong>Host</strong> element, each representing a different web
  application associated with this virtual host.  In addition, you can nest a
  single <a href="defaultcontext.html">DefaultContext</a> element that defines
  default values for subsequently deployed web applications.</p>

  <p>You can optional nest a <a href="defaultcontext.html">DefaultContext</a>
  element inside this <strong>Host</strong> element, to define the default
  characteristics of web applications that are automatically deployed.</p>

  <p>You can nest at most one instance of the following utility components
  by nesting a corresponding element inside your <strong>Host</strong>
  element:</p>
  <ul>
  <li><a href="realm.html"><strong>Realm</strong></a> -
      Configure a realm that will allow its
      database of users, and their associated roles, to be shared across all
      <a href="context.html">Contexts</a> nested inside this Host (unless
      overridden by a <a href="realm.html">Realm</a> configuration
      at a lower level).</li>
  </ul>

</section>


<section name="Special Features">


  <subsection name="Logging">

    <p>A host is associated with the 
       <code>org.apache.catalina.core.ContainerBase.[enginename].[hostname]</code>
       log category.  Note that the brackets are actuall part of the name,
       don't omit them.</p>

  </subsection>


  <subsection name="Access Logs">

    <p>When you run a web server, one of the output files normally generated
    is an <em>access log</em>, which generates one line of information for
    each request processed by the server, in a standard format.  Catalina
    includes an optional <a href="valve.html">Valve</a> implementation that
    can create access logs in the same standard format created by web servers,
    or in any number of custom formats.</p>

    <p>You can ask Catalina to create an access log for all requests
    processed by an <a href="engine.html">Engine</a>,
    <a href="host.html">Host</a>, or <a href="context.html">Context</a>
    by nesting a <a href="valve.html">Valve</a> element like this:</p>

<source>
&lt;Host name="localhost" ...&gt;
  ...
  &lt;Valve className="org.apache.catalina.valves.AccessLogValve"
         prefix="localhost_access_log." suffix=".txt"
         pattern="common"/&gt;
  ...
&lt;/Host&gt;
</source>

    <p>See <a href="valve.html#Access Log Valve">Access Log Valve</a>
    for more information on the configuration attributes that are
    supported.</p>

  </subsection>


  <subsection name="Automatic Application Deployment">

    <p>If you are using the standard <strong>Host</strong> implementation,
    the following actions take place automatically when Catalina is first
    started, if the <code>deployOnStartup</code> property is set to
    <code>true</code> (which is the default value):</p>
    <ul>
    <li>Any XML file in the 
        <code>$CATALINA_HOME/conf/[engine_name]/[host_name]</code> directory is
        assumed to contain a
        <a href="context.html">Context</a> element (and its associated
        subelements) for a single web application.  The <code>docBase</code>
        attribute of this <code>&lt;Context&gt;</code> element will typically
        be the absolute pathname to a web application directory, or the
        absolute pathname of a web application archive (WAR) file (which
        will not be expanded).</li>
    <li>Any web application archive file within the application base (appBase)
        directory that does not have a corresponding
        directory of the same name (without the ".war" extension) will be
        automatically expanded, unless the <code>unpackWARs</code> property
        is set to <code>false</code>.  If you redeploy an updated WAR file,
        be sure to delete the expanded directory when restarting Tomcat, so
        that the updated WAR file will be re-expanded (note that the auto
        deployer, if enabled, will automatically expand the updated WAR file
        once the previously expanded directory is removed).</li>
    <li>Any subdirectory within the <em>application base directory</em>
        that appears to be an unpacked web application (that is, it contains
        a <code>/WEB-INF/web.xml</code> file) will receive an automatically
        generated <a href="context.html">Context</a> element, even if this
        directory is not mentioned in the <code>conf/server.xml</code> file.
        This generated Context entry will be configured according to the
        properties set in any <a href="defaultcontext.html">DefaultContext</a>
        element nested in this Host element.  The context path for this
        deployed Context will be a slash character ("/") followed by the
        directory name, unless the directory name is ROOT, in which case
        the context path will be an empty string ("").</li>
    </ul>

    <p>In addition to the automatic deployment that occurs at startup time,
    you can also request that new XML configuration files, WAR files, or
    subdirectories (containing web applications) that are dropped in to the
    <code>appBase</code> (or 
    <code>$CATALINA_HOME/conf/[engine_name]/[host_name]</code> in the case of
    an XML configuration file) directory while Tomcat is running will be
    automatically deployed, according to the rules described above. The 
    auto deployer will also track web applications for the following changes:
    <ul>
        <li>An update to the WEB-INF/web.xml file will trigger a reload of the
        web application</li>
        <li>An update to a WAR which has been expanded will trigger 
        an undeploy (<strong>with a removal of the expanded webapp</strong>), 
        followed by a deployment</li>
        <li>An update to a XML configuration file will trigger an undeploy
        (without the removal of any expanded directory), followed by 
        a deployment of the associated web application</li>
    </ul>
    </p>

    <p>When using automatic deployment, the <code>docBase</code> defined by
    an XML <a href="context.html">Context</a> file should be outside of the
    <code>appBase</code> directory. If this is not the case difficulties
    may be experienced deploying the web application or the application may
    be deployed twice.</p>

    <p>Finally, note that if you are defining contexts explicitly, you should
    probably turn off automatic application deployment.  Otherwise, your context
    will be deployed twice each, and that may cause problems for your app.
    </p>

  </subsection>


  <subsection name="Host Name Aliases">

    <p>In many server environments, Network Administrators have configured
    more than one network name (in the <em>Domain Name Service</em> (DNS)
    server), that resolve to the IP address of the same server.  Normally,
    each such network name would be configured as a separate
    <strong>Host</strong> element in <code>conf/server.xml</code>, each
    with its own set of web applications.</p>

    <p>However, in some circumstances, it is desireable that two or more
    network names should resolve to the <strong>same</strong> virtual host,
    running the same set of applications.  A common use case for this
    scenario is a corporate web site, where it is desireable that users
    be able to utilize either <code>www.mycompany.com</code> or
    <code>company.com</code> to access exactly the same content and
    applications.</p>

    <p>This is accomplished by utilizing one or more <strong>Alias</strong>
    elements nested inside your <strong>Host</strong> element.  For
    example:</p>
<source>
&lt;Host name="www.mycompany.com" ...&gt;
  ...
  &lt;Alias&gt;mycompany.com&lt;/Alias&gt;
  ...
&lt;/Host&gt;
</source>

    <p>In order for this strategy to be effective, all of the network names
    involved must be registered in your DNS server to resolve to the
    same computer that is running this instance of Catalina.</p>

  </subsection>


  <subsection name="Lifecycle Listeners">

    <p>If you have implemented a Java object that needs to know when this
    <strong>Host</strong> is started or stopped, you can declare it by
    nesting a <strong>Listener</strong> element inside this element.  The
    class name you specify must implement the
    <code>org.apache.catalina.LifecycleListener</code> interface, and
    it will be notified about the occurrence of the coresponding
    lifecycle events.  Configuration of such a listener looks like this:</p>

<source>
&lt;Host name="localhost" ...&gt;
  ...
  &lt;Listener className="com.mycompany.mypackage.MyListener" ... &gt;
  ...
&lt;/Host&gt;
</source>

    <p>Note that a Listener can have any number of additional properties
    that may be configured from this element.  Attribute names are matched
    to corresponding JavaBean property names using the standard property
    method naming patterns.</p>

  </subsection>


  <subsection name="Request Filters">

    <p>You can ask Catalina to check the IP address, or host name, on every
    incoming request directed to the surrounding
    <a href="engine.html">Engine</a>, <a href="host.html">Host</a>, or
    <a href="context.html">Context</a> element.  The remote address or name
    will be checked against a configured list of "accept" and/or "deny"
    filters, which are defined using the Regular Expression syntax supported
    by the <a href="http://jakarta.apache.org/regexp/">Jakarta Regexp</a>
    regular expression library.  Requests that come from locations that are
    not accepted will be rejected with an HTTP "Forbidden" error.
    Example filter declarations:</p>

<source>
&lt;Host name="localhost" ...&gt;
  ...
  &lt;Valve className="org.apache.catalina.valves.RemoteHostValve"
         allow="*.mycompany.com,www.yourcompany.com"/&gt;
  &lt;Valve className="org.apache.catalina.valves.RemoteAddrValve"
         deny="192.168.1.*"/&gt;
  ...
&lt;/Host&gt;
</source>

  <p>See <a href="valve.html#Remote Address Filter">Remote Address Filter</a>
  and <a href="valve.html#Remote Host Filter">Remote Host Filter</a> for
  more information about the configuration options that are supported.</p>

  </subsection>


  <subsection name="Single Sign On">

    <p>In many environments, but particularly in portal environments, it
    is desireable to have a user challenged to authenticate themselves only
    once over a set of web applications deployed on a particular virtual
    host.  This can be accomplished by nesting an element like this inside
    the Host element for this virtual host:</p>

<source>
&lt;Host name="localhost" ...&gt;
  ...
  &lt;Valve className="org.apache.catalina.authenticator.SingleSignOn"
         debug="0"/&gt;
  ...
&lt;/Host&gt;
</source>

    <p>The Single Sign On facility operates according to the following rules:
    </p>
    <ul>
    <li>All web applications configured for this virtual host must share the
        same <a href="realm.html">Realm</a>.  In practice, that means you can
        nest the Realm element inside this Host element (or the surrounding
        <a href="engine.html">Engine</a> element), but not inside a
        <a href="context.html">Context</a> element for one of the involved
        web applications.</li>
    <li>As long as the user accesses only unprotected resources in any of the
        web applications on this virtual host, they will not be challenged
        to authenticate themselves.</li>
    <li>As soon as the user accesses a protected resource in
        <strong>any</strong> web application associated with this virtual
        host, the user will be challenged to authenticate himself or herself,
        using the login method defined for the web application currently
        being accessed.</li>
    <li>Once authenticated, the roles associated with this user will be
        utilized for access control decisions across <strong>all</strong>
        of the associated web applications, without challenging the user
        to authenticate themselves to each application individually.</li>
    <li>As soon as the user logs out of one web application (for example,
        by invalidating the corresponding session if form
        based login is used), the user's sessions in <strong>all</strong>
        web applications will be invalidated.  Any subsequent attempt to
        access a protected resource in any application will require the
        user to authenticate himself or herself again.</li>
    <li>The Single Sign On feature utilizes HTTP cookies to transmit a token
        that associates each request with the saved user identity, so it can
        only be utilized in client environments that support cookies.</li>
    </ul>

  </subsection>


  <subsection name="User Web Applications">

    <p>Many web servers can automatically map a request URI starting with
    a tilde character ("~") and a username to a directory (commonly named
    <code>public_html</code>) in that user's home directory on the server.
    You can accomplish the same thing in Catalina by using a special
    <strong>Listener</strong> element like this (on a Unix system that
    uses the <code>/etc/passwd</code> file to identify valid users):</p>

<source>
&lt;Host name="localhost" ...&gt;
  ...
  &lt;Listener className="org.apache.catalina.startup.UserConfig"
            directoryName="public_html"
            userClass="org.apache.catalina.startup.PasswdUserDatabase"/&gt;
  ...
&lt;/Host&gt;
</source>

    <p>On a server where <code>/etc/passwd</code> is not in use, you can
    request Catalina to consider all directories found in a specified base
    directory (such as <code>c:\Homes</code> in this example) to be
    considered "user home" directories for the purposes of this directive:</p>

<source>
&lt;Host name="localhost" ...&gt;
  ...
  &lt;Listener className="org.apache.catalina.startup.UserConfig"
            directoryName="public_html"
            homeBase=c:\Homes"
            userClass="org.apache.catalina.startup.HomesUserDatabase"/&gt;
  ...
&lt;/Host&gt;
</source>

    <p>If a user home directory has been set up for a user named
    <code>craigmcc</code>, then its contents will be visible from a
    client browser by making a request to a URL like:</p>

<source>
http://www.mycompany.com:8080/~craigmcc
</source>

    <p>Successful use of this feature requires recognition of the following
    considerations:</p>
    <ul>
    <li>Each user web application will be deployed with characteristics
        established by any <a href="defaultcontext.html">DefaultContext</a>
        element you have configured for this Host.</li>
    <li>It is legal to include more than one instance of this Listener
        element.  This would only be useful, however, in circumstances
        where you wanted to configure more than one "homeBase" directory.</li>
    <li>The operating system username under which Catalina is executed
        MUST have read access to each user's web application directory,
        and all of its contents.</li>
    </ul>

  </subsection>


</section>


</body>


</document>
