<?xml version="1.0"?>
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<!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="Table of Contents">
<toc/>
</section>

<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_BASE to refer the
    base directory against which most relative paths are resolved. If you have
    not configured Tomcat for multiple instances by setting a CATALINA_BASE
    directory, then $CATALINA_BASE will be set to the value of $CATALINA_HOME,
    the directory into which you have installed Tomcat.</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, 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. If not specified, the default of
        <code>webapps</code> will be used.</p>
      </attribute>

      <attribute name="autoDeploy" required="false">
        <p>This flag value indicates if Tomcat should check periodically for new
        or updated web applications while Tomcat is running. If true, Tomcat
        periodically checks the <code>appBase</code> and
        <code>$CATALINA_BASE/conf/[engine_name]/[host_name]</code>
        directories and deploys any new web applications or context XML
        descriptors found. Updated web applications or context XML descriptors
        will trigger a reload of the web application. 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="deployIgnore" required="false">
        <p>A regular expression defining paths to ignore when
        <code>autoDeploy</code> and <code>deployOnStartup</code> are set. This
        allows you to keep your configuration in a version control system, for
        example, and not deploy a .svn or CVS folder that happens to be in the
        <code>appBase</code>.</p>
        <p>This regular expression is relative to <code>appBase</code>. It is
        also <em>anchored</em>, meaning the match is performed against the
        entire file/directory name. So, <code>foo</code> matches only a file or
        directory named <code>foo</code> but not <code>foo.war</code>,
        <code>foobar</code>, or <code>myfooapp</code>. To match anything with
        &quot;foo&quot;, you could use <code>.*foo.*</code>.</p>
        <p>See <a href="#Automatic_Application_Deployment">Automatic Application
        Deployment</a> for more information.</p>
      </attribute>

      <attribute name="deployOnStartup" required="false">
        <p>This flag value indicates if web applications from this host should
        be automatically deployed when Tomcat starts. 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. Regardless of the case used to
        specify the hostname, Tomcat will convert it to lower case internally.
        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 descriptor embedded inside the application (located at
        <code>/META-INF/context.xml</code>). Security conscious 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 putting it in
        <code>$CATALINA_BASE/conf/[engine_name]/[host_name]</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 responsibility 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. WAR files located outside of the Host's
        <strong>appBase</strong> will not be expanded. 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_BASE/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.</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.[engine_name].[host_name]</code>
       log category.  Note that the brackets are 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
        <code>$CATALINA_BASE/conf/[engine_name]/[host_name]</code> is
        assumed to be a context XML descriptor containing a
        <a href="context.html">Context</a> element (and its associated
        sub-elements) for a single web application. The web applications
        associated with each of these context XML descriptor files will be
        deployed first.<br/>
        The <code>docBase</code> attribute of this <code>&lt;Context&gt;</code>
        element must only be set if the docBase is outside the Host's
        <code>appBase</code>. For web applications located inside the Host's
        <code>appBase</code>, the <code>docBase</code> will be the name of the
        XML file with ".xml" replaced with ".war" for a web application archive
        or the name of the XML file with ".xml" removed for a directory.<br/>
        The <code>path</code> attribute must not be set. The context path used
        will be a slash character ("/") followed by the name of the XML file
        (less the .xml extension). Multi-level context paths may be defined
        using #, e.g. <code>foo#bar.xml</code> for a context path of
        <code>/foo/bar</code>. The default web application that has a context
        path of <code>/</code> may be defined by using a file called
        <code>ROOT.xml</code>.</li>
    <li>Any web application archive file within the Host's <code>appBase</code>
        directory that has not already been deployed as a result of a context
        XML descriptor, does not have a corresponding directory of the same
        name (without the ".war" extension), and is not excluded by
        <code>deployIgnore</code> will be deployed next. The context path
        used will be a slash character ("/") followed by the web application
        archive name less the ".war" extension. The one exception to this rule
        is that a web application archive named "ROOT.war" will be deployed with
        a context path of <code>/</code>. Multi-level contexts may be defined by
        using #, e.g. use a WAR named <code>foo#bar.war</code> for a context
        path of <code>/foo/bar</code>.<br/>
        If the <code>unpackWARs</code> attribute is <code>true</code>, the web
        application archive file will be expanded to a directory of the same
        name (without the ".war" extension".<br/>
        Note: If you re-deploy an updated WAR file while Tomcat is stopped, be
        sure to delete the associated expanded directory before restarting 
        Tomcat, so that the updated WAR file will be re-expanded when Tomcat
        restarts.<br/>
        Any web application archive file within the Hosts's <code>appBase</code>
        directory that does not have a corresponding context XML descriptor
        (with a ".xml" extension rather than a ".war" extension) in 
        <code>$CATALINA_BASE/conf/[engine_name]/[host_name]</code> will be
        scanned to see if it contains a context XML descriptor (located at
        <code>/META-INF/context.xml</code>) and if one is found the descriptor
        will be copied to the
        <code>$CATALINA_BASE/conf/[engine_name]/[host_name]</code> directory and
        renamed.
        </li>
    <li>Finally, any sub-directory within the Host's <code>appBase</code> that
        has not already been deployed as a result of a context XML descriptor
        and is not excluded by <code>deployIgnore</code> will be deployed.
        The context path used will be a slash character ("/") followed by the
        directory name, unless the directory name is ROOT, in which case the
        context path will <code>/</code>. Multi-level contexts may be defined by
        using #, e.g. use a directory named <code>foo#bar</code> for a context
        path of <code>/foo/bar</code>.<br/>
        Any directory within the Hosts's <code>appBase</code> directory that
        does not have a corresponding context XML descriptor in
        <code>$CATALINA_BASE/conf/[engine_name]/[host_name]</code> will be
        scanned to see if it contains a context XML descriptor (located at
        <code>/META-INF/context.xml</code>) and if one is found the descriptor
        will be copied to
        <code>$CATALINA_BASE/conf/[engine_name]/[host_name]</code> and renamed.
        </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
    sub-directories that are dropped in to the <code>appBase</code> (or 
    <code>$CATALINA_BASE/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>Deleting a WAR file will trigger an undeploy of the application with
          the removal of any associated expanded directory, context file and
          work directory. Any current user sessions will not be persisted.</li>
        <li>Deleting a directory will trigger an undeploy of the application
          with the removal of any associated context file and work directory.
          Any current user sessions will not be persisted. If there is an
          associated WAR file, it will not be deleted and the application will
          be redeployed from the WAR file the next time the auto deployer checks
          for changes.</li>
        <li>Deleting a context file will trigger an undeploy of the application
          with the removal of any associated work directory. Any current user
          sessions will not be persisted. If there is an associated WAR file
          and/or directory, they will not be deleted and the application will be
          redeployed from the WAR file (or from directory if there is no WAR
          file) the next time the auto deployer checks for changes.</li>
        <li>Updating a WAR file will trigger an undeploy of the application with
          the removal of any associated expanded directory, context file and
          work directory. Any current user sessions will not be persisted.</li>
        <li>Updating a directory (not the directory contents) will trigger an
          undeploy of the application with the removal of any associated context
          file and work directory. Any current user sessions will not be
          persisted. The application will be redeployed the next time the auto
          deployer checks for changes.</li>
        <li>Updating a context file will trigger an undeploy of the application
          with the removal of any associated work directory. Any current user
          sessions will not be persisted. The application will be redeployed the
          next time the auto deployer checks for changes.</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. The <code>deployIgnore</code> attribute can be used
    to avoid this situation.</p>

    <p>Finally, note that if you are defining contexts explicitly in server.xml,
    you should probably turn off automatic application deployment or specify
    <code>deployIgnore</code> carefully. Otherwise, the web applications
    will each be deployed twice, and that may cause problems for the
    applications.</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 desirable 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 desirable 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 corresponding
    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 <code>java.util.regex</code> Regular
    Expression syntax.  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\.\d+"/&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"/&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 the global and host level default context settings.</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>
