Top Ten Tomcat Configuration Tipsby Jason Brittain and Ian F. Darwin, authors of Tomcat: The Definitive Guide
Coauthor's note: Now that writing Java web applications has become a common way to create and deploy new web content, people around the globe are finding the Jakarta Tomcat servlet and JSP container useful. It's free, it's multiplatform, it's rich in features, it's rapidly evolving and improving, and it's never been more popular.
The only catch seems to be this: how can you configure Tomcat to do what you want it to do? Tomcat is capable, as long as you can configure it to suit your needs. Below is my list of ten Tomcat configuration tips, taken from Tomcat: The Definitive Guide, to help you do just that. -- Jason Brittain
Most commercial J2EE servers provide a fully functional administrative interface, and many of these are accessible as web applications. The Tomcat Admin application is on its way to becoming a full-blown Tomcat administration tool rivaling these commercial offerings. First included in Tomcat 4.1, Admin already provides control over contexts, data sources, and users and groups. You can also control resources such as initialization parameters, as well as users, groups, and roles in a variety of user databases. The list of capabilities will be expanded upon in future releases, but the present implementation has proven itself to be quite useful.
The Admin web application is defined in the auto-deployment file CATALINA_BASE/webapps/admin.xml.
You must edit this file to ensure that the path specified in
docBase attribute of the
Context element is absolute; that is,
the absolute path of CATALINA_HOME/server/webapps/admin.
Alternatively, you could just remove the auto-deployment file
and specify the Admin context manually in your server.xml
file. On machines that will not be managed by this application,
you should probably disable it altogether by simply removing
If you're using a
UserDatabaseRealm (the default), you'll
need to add a user and a role to the CATALINA_BASE/conf/tomcat-users.xml file.
For now, just edit this file, and add a role named "admin" to your users
You must also have a user who is assigned to the "admin" role. Add a user line like this after the existing user entries (changing the password to something a bit more secure):
<user name="admin" password="deep_dark_secret" roles="admin"/>
Once you've performed these steps and restarted Tomcat, visit the URL http://localhost:8080/admin, and you should see a login screen. The Admin application is built using container-managed security and the Jakarta Struts framework. Once you have logged in as a user assigned to the admin role, you will be able to use the Admin application to configure Tomcat.
The Manager web application lets you perform simple management tasks on your web applications through a more simplified web user interface than that of the Admin web app.
The Manager web application is defined in the auto-deployment file CATALINA_BASE/webapps/manager.xml.
You must edit this file to ensure that the path specified in
docBase attribute of the
Context element is absolute; that is,
the absolute path of CATALINA_HOME/server/webapps/manager.
If you're using the default
need to add a user and role to the CATALINA_BASE/conf/tomcat-users.xml
file. For now, just edit this file, and add a role named "manager"
to your users database:
You must also have a user who is assigned the "manager" role. Add a user line like this after the existing user entries (changing the password to something a bit more secure):
<user name="manager" password="deep_dark_secret" roles="manager"/>
Then restart Tomcat and visit the URL http://localhost/manager/list to see the plain-text manager interface, or http://localhost/manager/html/list for the simple HTML manager interface. Either way, your Manager application should now be working.
The Manager application lets you install new web applications
on a non-persistent basis, for testing. If we have a web
application in /home/user/hello and want to test it by
installing it under the URI
/hello, we put "/hello" in the first
text input field (for Path) and "file:/home/user/hello" in the
second text input field (for Config URL).
The Manager also allows you to stop, reload, remove, or undeploy a web application. Stopping an application makes it unavailable until further notice, but of course it can then be restarted. Users attempting to access a stopped application will receive an error message, such as 503 - This application is not currently available.
Removing a web application removes it only from the running copy of Tomcat -- if it was started from the configuration files, it will reappear the next time you restart Tomcat (i.e., removal does not remove the web application's content from disk).
There are two ways of deploying a web application on the filesystem:
1. Copy your WAR file or your web application's directory (including all of its content) to the $CATALINA_BASE/webapps directory.
2. Create an XML fragment file with just the
Context element for
your web application, and place this XML file in
$CATALINA_BASE/webapps. The web application itself can then be
stored anywhere on your filesystem.
If you have a WAR file, you can deploy it by simply copying
the WAR file into the directory CATALINA_BASE/webapps. The
filename must end with an extension of ".war". Once Tomcat
notices the file, it will (by default) unpack it into a
subdirectory with the base name of the WAR file. It will then
create a context in memory, just as though you had created one
by editing Tomcat's server.xml file. However, any necessary
defaults will be obtained from the
DefaultContext element in
Tomcat's server.xml file.
Another way to deploy a web app is by writing a Context XML
fragment file and deploying it into the CATALINA_BASE/webapps
directory. A context fragment is not a complete XML document,
but just one
Context element and any subelements that are
appropriate for your web application. These files are like
Context elements cut out of the server.xml file, hence the name
For example, if we wanted to deploy the WAR file MyWebApp.war along with a realm for accessing parts of that web application, we could use this fragment:
<!-- Context fragment for deploying MyWebApp.war --> <Context path="/demo" docBase="webapps/MyWebApp.war" debug="0" privileged="true"> <Realm className="org.apache.catalina.realm.UserDatabaseRealm" resourceName="UserDatabase"/> </Context>
Put that in a file called "MyWebApp.xml," and copy it into your CATALINA_BASE/webapps directory.
These context fragments provide a convenient method of
deploying web applications; you do not need to edit the
server.xml file and, unless you have turned off the default
liveDeploy feature, you don't have to restart Tomcat to install
a new web application.
Host element normally needs modification only when you
are setting up virtual hosts. Virtual hosting is a mechanism
whereby one web server process can serve multiple domain names,
giving each domain the appearance of having its own server. In
fact, the majority of small business web sites are implemented
as virtual hosts, due to the expense of connecting a computer
directly to the Internet with sufficient bandwidth to provide
reasonable response times and the stability of a permanent IP
Name-based virtual hosting is created on any web server by establishing an aliased IP address in the Domain Name Service (DNS) data and telling the web server to map all requests destined for the aliased address to a particular directory of web pages. Since this article is about Tomcat, we don't try to show all of the ways to set up DNS data on various operating systems. If you need help with this, please refer to DNS and Bind, by Paul Albitz and Cricket Liu (O'Reilly). For demonstration purposes, I'll use a static hosts file, since that's the easiest way to set up aliases for testing purposes.
To use virtual hosts in Tomcat, you just need to set up the DNS or hosts data for the host. For testing, making an IP alias for localhost is sufficient. You then need to add a few lines to the server.xml configuration file:
<Server port="8005" shutdown="SHUTDOWN" debug="0"> <Service name="Tomcat-Standalone"> <Connector className="org.apache.coyote.tomcat4.CoyoteConnector" port="8080" minProcessors="5" maxProcessors="75" enableLookups="true" redirectPort="8443"/> <Connector className="org.apache.coyote.tomcat4.CoyoteConnector" port="8443" minProcessors="5" maxProcessors="75" acceptCount="10" debug="0" scheme="https" secure="true"/> <Factory className="org.apache.coyote.tomcat4.CoyoteServerSocketFactory" clientAuth="false" protocol="TLS" /> </Connector> <Engine name="Standalone" defaultHost="localhost" debug="0"> <!-- This Host is the default Host --> <Host name="localhost" debug="0" appBase="webapps" unpackWARs="true" autoDeploy="true"> <Context path="" docBase="ROOT" debug="0"/> <Context path="/orders" docBase="/home/ian/orders" debug="0" reloadable="true" crossContext="true"> </Context> </Host> <!-- This Host is the first "Virtual Host": www.example.com --> <Host name="www.example.com" appBase="/home/example/webapp"> <Context path="" docBase="."/> </Host> </Engine> </Service> </Server>
Tomcat's server.xml file, as distributed, contains only one
virtual host, but it is easy to add support for additional
virtual hosts. The simplified version of the server.xml file in
the previous example shows in bold the overall additional
structure needed to add one virtual host. Each
Host element must
have one or more
Context elements within it; one of these must
be the default
Context for this host, which is specified by
having its relative path set to the empty string (for example,
Container-managed authentication methods control how a user's
credentials are verified when a web app's protected resource is
accessed. When a web application uses basic authentication
BASIC in the web.xml file's
auth-method element), Tomcat uses
HTTP basic authentication to ask the web browser for a username
and password whenever the browser requests a resource of that
protected web application. With this authentication method, all
passwords are sent across the network in base64-encoded
Note: using basic authentication is generally considered
insecure because it does not strongly encrypt passwords, unless
the site also uses HTTPS or some other form of encryption
between the client and the server (for instance, a virtual
private network). Without this extra encryption, network
monitors can intercept (and misuse) users' passwords. But, if
you're just starting to use Tomcat, or if you just want to test
container-managed security with your web app, basic
authentication is easy to set up and test. Just add
<login-config> elements to
your web app's web.xml file, and add the appropriate
<user> elements to your
CATALINA_BASE/conf/tomcat-users.xml file, restart Tomcat, and
Tomcat takes care of the rest.
The example below shows a web.xml excerpt from a club membership web site with a members-only subdirectory that is protected using basic authentication. Note that this effectively takes the place of the Apache web server's .htaccess files.
<!-- Define the Members-only area, by defining a "Security Constraint" on this Application, and mapping it to the subdirectory (URL) that we want to restrict. --> <security-constraint> <web-resource-collection> <web-resource-name> Entire Application </web-resource-name> <url-pattern>/members/*</url-pattern> </web-resource-collection> <auth-constraint> <role-name>member</role-name> </auth-constraint> </security-constraint> <!-- Define the Login Configuration for this Application --> <login-config> <auth-method>BASIC</auth-method> <realm-name>My Club Members-only Area</realm-name> </login-config>
Once you've set up your realm and method of authentication, you'll need to deal with the actual process of logging the user in. More often than not, logging into an application is a nuisance to an end user, and you will need to minimize the number of times they must authenticate. By default, each web application will ask the user to log in the first time the user requests a protected resource. This can seem like a hassle to your users if you run multiple web applications and each application asks the user to authenticate. Users cannot tell how many separate applications make up any single web site, so they won't know when they're making a request that crosses a context boundary, and will wonder why they're being repeatedly asked to log in.
The "single sign-on" feature of Tomcat 4 allows a user to
authenticate only once to access all of the web applications
loaded under a virtual host. To use this feature, you need only
Valve element at the host level. This looks
like the following:
<Valve className="org.apache.catalina.authenticator.SingleSignOn" debug="0"/>
The Tomcat distribution's default server.xml contains a
commented-out single sign-on
Valve configuration example that
you can uncomment and use. Then, any user who is considered
valid in a context within the configured virtual host will be
considered valid in all other contexts for that same host.
There are several important restrictions for using the single sign-on valve:
The valve must be configured and nested within the same
Host element that the web applications (represented by
elements) are nested within.
Realm that contains the shared user information must
be configured either at the level of the same
Host or in an
Realm cannot be overridden at the
The web applications that use single sign-on must use one
of Tomcat's built-in authenticators (in the
<auth-method> element of web.xml), rather than a custom
authenticator. The built-in methods are
If you're using single sign-on and wish to integrate another third-party web application into your web site, and the new web application uses only its own authentication code that doesn't use container-managed security, you're basically stuck. Your users will have to log in once for all of the web applications that use single sign-on, and then once again if they make a request to the new third-party web application. Of course, if you get the source and you're a developer, you could fix it, but that's probably not so easy to do.
The single sign-on valve requires the use of HTTP cookies.
Some sites like to allow individual users to publish a directory of web pages on the server. For example, a university department might want to give each student a public area, or an ISP might make some web space available on one of its servers to customers that don't have a virtually hosted web server. In such cases, it is typical to use the tilde character (~) plus the user's name as the virtual path of that user's web site:
Tomcat gives you two ways to map this on a per-host basis,
using a couple of special
Listener elements. The
className attribute should be
org.apache.catalina.startup.UserConfig, with the
specifying one of several mapping classes. If your system runs
Unix, has a standard /etc/passwd file that is readable by the
account running Tomcat, and that file specifies users' home
directories, use the
PasswdUserDatabase mapping class:
<Listener className="org.apache.catalina.startup.UserConfig" directoryName="public_html" userClass="org.apache.catalina.startup.PasswdUserDatabase"/>
Web files would need to be in directories such as /home/users/ian/public_html or /users/jbrittain/public_html. Of course, you can change public_html to be whatever subdirectory into which your users put their personal web pages.
In fact, the directories don't have to be inside of a user's
home directory at all. If you don't have a password file but
want to map from a user name to a subdirectory of a common
parent directory such as /home, use the
<Listener className="org.apache.catalina.startup.UserConfig" directoryName="public_html" homeBase="/home" userClass="org.apache.catalina.startup.HomesUserDatabase"/>
In this case, web files would be in directories such as /home/ian/public_html or /home/jasonb/public_html. This format is more useful on Windows, where you'd likely use a directory such as C:\home.
Listener elements, if present, must be inside of a
element, but not inside of a
Context element, as they apply to the
Tomcat is primarily meant to be a servlet/JSP container, but
it has many capabilities rivalling a traditional web server. One
of these is support for the Common Gateway Interface (CGI),
which provides a means for running an external program in
response to a browser request, typically to process a web-based
form. CGI is called "common" because it can invoke programs in
almost any programming or scripting language: Perl, Python,
Unix shell scripting, and even Java are all supported
options. However, you probably wouldn't run a Java application as
a CGI due to the start-up overhead; elimination of this overhead
was what led to the original design of the servlet
specification. Servlets are almost always more efficient than
CGIs because you're not starting up a new operating-system-level
process every time somebody clicks on a link or button.
Tomcat includes an optional CGI servlet that allows you to run legacy CGI scripts; the assumption is that most new back-end processing will be done by user-defined servlets and JSPs.
To enable Tomcat's CGI servlet, you must do the following:
Rename the file servlets-cgi.renametojar (found in
CATALINA_HOME/server/lib/) to servlets-cgi.jar, so that the
servlet that processes CGI scripts will be on Tomcat's
In Tomcat's CATALINA_BASE/conf/web.xml file, uncomment the
definition of the servlet named
cgi (this is around line 241
in the distribution).
Also in Tomcat's web.xml, uncomment the servlet mapping
cgi servlet (around line 299 in the distributed
file). Remember, this specifies the HTML links to the CGI
Either place the CGI scripts under the WEB-INF/cgi
directory (remember that WEB-INF is a safe place to hide
things that you don't want the user to be able to view, for
security reasons), or place them in some other directory
within your context and adjust the
initialization parameter of the
CGIServlet to identify the
directory containing the files. This specifies the actual
location of the CGI scripts, which typically will not be the
same as the URL in the previous step.
Restart Tomcat, and your CGI processing should now be operational.
The default directory for the servlet to locate the actual scripts is WEB-INF/cgi. As has been noted, the WEB-INF directory is protected against casual snooping from browsers, so this is a good place to put CGI scripts, which may contain passwords or other sensitive information. For compatibility with other servers, though, you may prefer to keep the scripts in the traditional directory, /cgi-bin, but be aware that files in this directory may be viewable by the curious web surfer. Also, on Unix, be sure that the CGI script files are executable by the user under which you are running Tomcat.
In Tomcat 4.1 (and above, presumably), compilation of JSPs
is performed by using the Ant program controller directly from
within Tomcat. This sounds a bit strange, but it's part of what
Ant was intended for; there is a documented API that lets
developers use Ant without starting up a new JVM. This is one
advantage of having Ant written in Java. Plus, it means you can
now use any compiler supported by the
javac task within Ant;
these are listed in the
javac page of the Apache Ant manual. It is
easy to use because you need only an
<init-param> with a
name of "compiler" and a value of one of the supported compiler
<servlet> <servlet-name>jsp</servlet-name> <servlet-class> org.apache.jasper.servlet.JspServlet </servlet-class> <init-param> <param-name>logVerbosityLevel</param-name> <param-value>WARNING</param-value> </init-param> <init-param> <param-name>compiler</param-name> <param-value>jikes</param-value> </init-param> <load-on-startup>3</load-on-startup> </servlet>
Of course, the given compiler must be installed on your
system, and the
CLASSPATH may need to be set, depending on which
compiler you choose.
Sometimes you'll only want to restrict access to Tomcat's web app
to only specified host names or IP addresses. This way, only clients
at those specified sites will be served content. Tomcat comes with
Valves that you can configure and use for this purpose:
Valves allow you to filter requests by host name or by
IP address, and to allow or deny hosts that match, similar to
the per-directory Allow/Deny directives in Apache
httpd. If you
run the Admin application, you might want to only allow access to it
from localhost, as follows:
<Context path="/path/to/secret_files" ...> <Valve className="org.apache.catalina.valves.RemoteAddrValve" allow="127.0.0.1" deny=""/> </Context>
If no allow pattern is given, then patterns that match the
deny attribute patterns will be rejected, and all others will be
allowed. Similarly, if no deny pattern is given, patterns that
allow attribute will be allowed, and all others will
Jason Brittain is a Senior Software Engineer at Symantec Corporation's Network and Gateway Security Solutions Team, working on the AntiSpam product. He has contributed to many Apache Jakarta projects, and has been an active open source software developer for several years.
Ian F. Darwin has worked in the computer industry for three decades: with Unix since 1980, Java since 1995, and OpenBSD since 1998. He is the author of two O'Reilly books, Checking C Programs with lint and Java Cookbook, and co-author of Tomcat: The Definitive Guide with Jason Brittain.
O'Reilly & Associates recently released (June 2003) Tomcat: The Definitive Guide.
Sample Chapter 6, "Tomcat Security," is available free online.
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