The Apache Tomcat Servlet/JSP Container

Apache Tomcat 7

Version 7.0.42, Jul 2 2013
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The Host Container

Table of Contents
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 Tomcat is running. For clients to be able to connect to a Tomcat server using its network name, 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.com and company.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 defaultHost attribute of that Engine.

Clients normally use host names to identify the server they wish to connect to. This host name is also included in the HTTP request headers. Tomcat extracts the host name from the HTTP headers and looks for a Host with a matching name. If no match is found, the request is routed to the default host. The name of the default host does not have to match a DNS name (although it can) since any request where the DNS name does not match the name of a Host element will be routed to the default host.

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.

Attributes
Common Attributes

All implementations of Host support the following attributes:

AttributeDescription
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, or a pathname that is relative to the $CATALINA_BASE directory. See Automatic Application Deployment for more information on automatic recognition and deployment of web applications. If not specified, the default of webapps will be used.

xmlBase

The XML Base directory for this virtual host. This is the pathname of a directory that may contain context XML descriptors 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_BASE directory. See Automatic Application Deployment for more information on automatic recognition and deployment of web applications. If not specified the default of conf/<engine_name>/<host_name> will be used.

createDirs

If set to true, Tomcat will attempt to create the directories defined by the attributes appBase and xmlBase during the startup phase. The default value is true. If set to true, and directory creation fails, an error message will be printed out but will not halt the startup sequence.

autoDeploy

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 appBase and xmlBase 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 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.Host interface. If not specified, the standard value (defined below) will be used.

deployIgnore

A regular expression defining paths to ignore when autoDeploy and deployOnStartup 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 appBase.

This regular expression is relative to appBase. It is also anchored, meaning the match is performed against the entire file/directory name. So, foo matches only a file or directory named foo but not foo.war, foobar, or myfooapp. To match anything with "foo", you could use .*foo.*.

See Automatic Application Deployment for more information.

deployOnStartup

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 Automatic Application Deployment for more information.

name

Usually the network name of this virtual host, as registered in your Domain Name Service server. Regardless of the case used to specify the host name, Tomcat will convert it to lower case internally. One of the Hosts nested within an Engine MUST have a name that matches the defaultHost setting for that Engine. See Host Name Aliases for information on how to assign more than one network name to the same virtual host.

startStopThreads

The number of threads this Host will use to start child Context elements in parallel. The same thread pool will be used to deploy new Contexts if automatic deployment is being used. The special value of 0 will result in the value of Runtime.getRuntime().availableProcessors() being used. Negative values will result in Runtime.getRuntime().availableProcessors() + value being used unless this is less than 1 in which case 1 thread will be used. If not specified, the default value of 1 will be used.

undeployOldVersions

This flag determines if Tomcat, as part of the auto deployment process, will check for old, unused versions of web applications deployed using parallel deployment and, if any are found, remove them. This flag only applies if autoDeploy is true. If not specified the default value of false will be used.

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):

AttributeDescription
copyXML

Set to true if you want a context XML descriptor embedded inside the application (located at /META-INF/context.xml) to be copied to xmlBase when the application is deployed. On subsequent starts, the copied context XML descriptor will be used in preference to any context XML descriptor embedded inside the application even if the descriptor embedded inside the application is more recent. The flag's value defaults to false. Note if deployXML is false, this attribute will have no effect.

deployXML

Set to false if you want to disable parsing the context XML descriptor embedded inside the application (located at /META-INF/context.xml). Security conscious environments should set this to false 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 the location defined by the xmlBase attribute. The flag's value defaults to true.

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.Valve interface. If none is specified, the value org.apache.catalina.valves.ErrorReportValve will be used by default.

unpackWARs

Set to true if you want web applications that are placed in the appBase directory as web application archive (WAR) files to be unpacked into a corresponding disk directory structure, false to run such web applications directly from a WAR file. WAR files located outside of the Host's appBase will not be expanded. See Automatic Application Deployment for more information.

workDir

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