| Apache Tomcat Configuration ReferenceThe Host Container| Introduction |  | 
  The Host element represents a virtual host,
  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
  Domain Name Service (DNS) server that manages the Internet
  domain you belong to - contact your Network Administrator for more
  information. In many cases, System Administrators wish to associate more than
  one network name (such as www.mycompany.comandcompany.com) with the same virtual host and applications.
  This can be accomplished using the Host
  Name Aliases feature discussed below. One or more Host elements are nested inside an
  Engine element.  Inside the Host element, you
  can nest Context 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
  defaultHostattribute of that Engine. 
    The description below uses the variable name $CATALINA_HOME
    to refer to the directory into which you have installed Tomcat 5,
    and is the base directory against which most relative paths are
    resolved.  However, if you have configured Tomcat 5 for multiple
    instances by setting a CATALINA_BASE directory, you should use
    $CATALINA_BASE instead of $CATALINA_HOME for each of these
    references. | 
 | Attributes |  | 
  | Common Attributes |  | 
    All implementations of Host
    support the following attributes: | Attribute | Description | 
|---|
 | appBase | The Application Base 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 $CATALINA_BASEdirectory.  See
        Automatic Application
        Deployment for more information on automatic recognition and
        deployment of web applications to be deployed automatically.If not
        specified, the default ofwebappswill be used. |  | autoDeploy | This flag value indicates if new web applications, dropped in to
        the appBasedirectory while Tomcat is running, should
        be automatically deployed.  The flag's value defaults to true.  See
        Automatic Application
        Deployment for more information. |  | backgroundProcessorDelay | 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. |  | className | Java class name of the implementation to use.  This class must
        implement the org.apache.catalina.Hostinterface.
        If not specified, the standard value (defined below) will be used. |  | deployOnStartup | 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
        Automatic Application
        Deployment for more information. |  | name | Network name of this virtual host, as registered in your
        Domain Name Service 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 Engine MUST
        have a name that matches the defaultHostsetting for that
        Engine.  See Host Name Aliases for
        information on how to assign more than one network name to the same
        virtual host. | 
 | 
 | Standard Implementation |  | 
    The standard implementation of Host is
    org.apache.catalina.core.StandardHost.
    It supports the following additional attributes (in addition to the
    common attributes listed above): | Attribute | Description | 
|---|
 | deployXML | Set to falseif you want to disable parsing the context.xml
        file embedded inside the application (located at/META-INF/context.xml). 
        Security conscious environments should set this tofalseto 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$CATALINA_HOME/conf/[enginename]/[hostname]/.
        The flag's value defaults totrue. |  | errorReportValveClass | 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
        org.apache.catalina.Valveinterface. If none is specified,
        the valueorg.apache.catalina.valves.ErrorReportValvewill be used by default. |  | unpackWARs | Set to trueif you want web applications that are
        placed in theappBasedirectory as web application
        archive (WAR) files to be unpacked into a corresponding disk directory
        structure,falseto run such web applications directly
        from a WAR file.  See
        Automatic Application
        Deployment for more information. |  | workDir | 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 java.io.File) namedjavax.servlet.context.tempdiras described in the
        Servlet Specification.  If not specified, a suitable directory
        underneath$CATALINA_HOME/workwill be provided. | 
 | 
 | 
 | Nested Components |  | 
  You can nest one or more Context elements
  inside this Host element, each representing a different web
  application associated with this virtual host. You can nest at most one instance of the following utility components
  by nesting a corresponding element inside your Host
  element: 
  Realm -
      Configure a realm that will allow its
      database of users, and their associated roles, to be shared across all
      Contexts nested inside this Host (unless
      overridden by a Realm configuration
      at a lower level). | 
 | Special Features |  | 
  | Logging |  | 
    A host is associated with the 
       org.apache.catalina.core.ContainerBase.[enginename].[hostname]log category.  Note that the brackets are part of the name,
       don't omit them. | 
 | Automatic Application Deployment |  | 
    If you are using the standard Host implementation,
    the following actions take place automatically when Catalina is first
    started, if the deployOnStartupproperty is set totrue(which is the default value): 
    Any XML file in the 
        $CATALINA_HOME/conf/[engine_name]/[host_name]directory is
        assumed to contain a
        Context element (and its associated
        subelements) for a single web application.  ThedocBaseattribute of this<Context>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). The path attribute will be automatically set
        as defined in the Context documentation.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 unpackWARsproperty
        is set tofalse.  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). Multi-level contexts
        may be defined by using #, eg use a WAR namedfoo#bar.warfor a context path of/foo/bar.Any subdirectory within the application base directory
        will receive an automatically generated 
        Context element, even if this directory is not mentioned in the
        conf/server.xmlfile.
        This generated Context entry will be configured according to the
        defaults configured for 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 (""). Multi-level contexts
        may be defined by using #, eg use a directory namedfoo#barfor a context path of/foo/bar. In addition to the automatic deployment that occurs at startup time,
    you can also request that new XML configuration files, WAR files, or
    subdirectories that are dropped in to the appBase(or$CATALINA_HOME/conf/[engine_name]/[host_name]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: 
        An update to the WEB-INF/web.xml file will trigger a reload of the
        web applicationAn update to a WAR which has been expanded will trigger 
        an undeploy (with a removal of the expanded webapp), 
        followed by a deploymentAn 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 When using automatic deployment, the docBasedefined by
    an XML Context file should be outside of theappBasedirectory. If this is not the case difficulties
    may be experienced deploying the web application or the application may
    be deployed twice. 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.
     | 
 | Single Sign On |  | 
    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: |  |  |  |  |  | 
<Host name="localhost" ...>
  ...
  <Valve className="org.apache.catalina.authenticator.SingleSignOn" />
  ...
</Host>
 |  |  |  |  |  | 
The Single Sign On facility operates according to the following rules:
     
    All web applications configured for this virtual host must share the
        same Realm.  In practice, that means you can
        nest the Realm element inside this Host element (or the surrounding
        Engine element), but not inside a
        Context element for one of the involved
        web applications.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.As soon as the user accesses a protected resource in
        any 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.Once authenticated, the roles associated with this user will be
        utilized for access control decisions across all
        of the associated web applications, without challenging the user
        to authenticate themselves to each application individually.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 all
        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.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. | 
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