Introduction

This document explains how to connect Tomcat to the popular open source web server, Apache. There is actually two version of Apache, 1.3 and 2.0 and both can be used with mod_jk, the Tomcat redirector module.

It is recommanded that you also read the Workers HowTo document to learn how to setup the working entities between your WebServer and Tomcat Engines.

This document was originally part of Tomcat: A Minimalistic User's Guide written by Gal Shachor, but has been split off for organizational reasons.

Document Conventions and Assumptions

${tomcat_home} is the root directory of tomcat. Your Tomcat installation should have the following subdirectories:

• ${tomcat_home}\conf - Where you can place various configuration files
• ${tomcat_home}\webapps - Containing example applications
• ${tomcat_home}\bin - Where you place web server plugins

In all the examples in this document ${tomcat_home} will be /var/tomcat3 . A worker is defined to be a tomcat process that accepts work from the Apache server.

Supported Configuration

The mod_jk module was developed and tested on:

• Linux, FreeBSD, AIX, HP-UX, MacOS X, and should works on major Unixes platforms supporting Apache 1.3 and/or 2.0
• WinNT4.0-i386 SP4/SP5/SP6a (should be able to work with other service packs), Win2K and WinXP and Win98
• Cygwin (until you have an apache server and autoconf/automake support tools)
• Netware
• iSeries V5R1 and V5R2 with Apache 2.0.39. Be sure to have the latest Apache PTF installed.
• Tomcat 3.2.x, Tomcat 3.3.x, Tomcat 4.0.x, Tomcat 4.1.x and Tomcat 5

The redirector uses ajp12 and ajp13 to send requests to the Tomcat containers. There is also an option to use Tomcat in process, more about the in-process mode can be found in the in process howto.

Who support ajp protocols ?

The ajp12 protocol is only available in Tomcat 3.2.x and 3.3.x.

The ajp12 has been deprecated with Tomcat 3.3.x and you should use instead ajp13 which is the only ajp protocol known by Tomcat 4.0.x, 4.1.x and 5.

Of course Tomcat 3.2.x and 3.3.x also support ajp13 protocol.

Others servlet engines such as jetty have support for ajp13 protocol

How does it work ?

In a nutshell a web server is waiting for client HTTP requests. When these requests arrive the server does whatever is needed to serve the requests by providing the necessary content.

Adding a servlet container may somewhat change this behavior. Now the web server needs also to perform the following:

• Load the servlet container adapter library and initialize it (prior to serving requests).
• When a request arrives, it needs to check and see if a certain request belongs to a servlet, if so it needs to let the adapter take the request and handle it.

The adapter on the other hand needs to know what requests it is going to serve, usually based on some pattern in the request URL, and to where to direct these requests.

Things are even more complex when the user wants to set a configuration that uses virtual hosts, or when they want multiple developers to work on the same web server but on different servlet container JVMs. We will cover these two cases in the advanced sections.

Obtaining mod_jk

mod_jk can be obtained in two formats - binary and source. Depending on the platform you are running your web server on, a binary version of mod_jk may be available.

It is recommended to use the binary version if one is available. If the binary is not available, follow the instructions for building mod_jk from source.

The binaries for mod_jk are now available, for several platforms, in a separate area as the Tomcat Binary Release. The binaries are located in subdirectories by platform.

For some platforms, such as Windows, this is the typical way of obtaining mod_jk since most Windows systems do not have C compilers.

For others, the binary distribution of mod_jk offers simpler installation.

For example JK 1.2.0 can be found here and contains the following:

If you don't see your Operating System here, the doc may be outdated so just go here and check if one of the directory didn't cover your os

Installation

mod_jk requires two entities:

• mod_jk.xxx - The Apache module, depending on your operating system, it will be mod_jk.so, mod_jk.dll, mod_jk,nlm or or QZTCJK.SRVPGM (see the build section).
• workers.properties - A file that describes the host(s) and port(s) used by the workers (Tomcat processes). A sample workers.properties can be found under the conf directory.

Also as with other Apache modules, mod_jk should be first installed on the modules directory of your Apache webserver, ie : /usr/lib/apache and you should update your httpd.conf file.

Disabling old mod_jserv

If you've previously configured Apache to use mod_jserv , remove any ApJServMount directives from your httpd.conf.

If you're including tomcat-apache.conf or tomcat.conf , you'll want to remove them as well - they are specific to mod_jserv .

The mod_jserv configuration directives are not compatible with mod_jk !

Using Tomcat auto-configure

The simplest way to configure Apache to use mod_jk is to turn on the Apache auto-configure setting in Tomcat and put the following include directive at the end of your Apache httpd.conf file (make sure you replace TOMCAT_HOME with the correct path for your Tomcat installation:

This will tell Apache to use directives in the mod_jk.conf-auto file in the Apache configuration. This file is created by enabling the Apache auto-configuration as described in the Tomcat documentation.

Custom mod_jk configuration

You should use custom configuration when :

• You couldn't use mod_jk.conf-auto since Tomcat engine isn't on the same machine that your Apache WebServer, ie when you have an Apache in front of a Tomcat Farm.
• Another case for custom configuration is when your Apache is in front of many differents Tomcat engines, each one having it's own configuration, a general case in ISP hosting
• Also all Apache webmaster will retain custom configuration to be able to tune the settings to their real needs.

Simple configuration example

Here is a simple configuration:

mod_jk Directives

We'll discuss here the mod_jk directives and details behind them

Define workers

JkWorkersFile specify the location where mod_jk will find the workers definitions.

Logging

JkLogFile specify the location where mod_jk is going to place its log file.

JkLogLevel set the log level between :

• info log will contains standard mod_jk activity (default).
• error log will contains also error reports.
• debug log will contains all informations on mod_jk activity

info should be your default selection for normal operations.

JkLogStampFormat will configure the date/time format found on mod_jk logfile. Using the strftime() format string it's set by default to "[%a %b %d %H:%M:%S %Y]"

JkRequestLogFormat will configure the format of mod_jk individual request logging. Request logging is configured and enabled on a per virtual host basis. To enable request logging for a virtual host just add a JkRequestLogFormat config. The syntax of the format string is similiar to the Apache LogFormat command, here is a list of the available request log format options:

Forwarding

The directive JkOptions allow you to set many forwarding options which will enable (+) or disable (-) following option.

JkOptions ForwardKeySize , you ask mod_jk, when using ajp13, to forward also the SSL Key Size as required by Servlet API 2.3. This flag shouldn't be set when servlet engine is Tomcat 3.2.x (on by default).

JkOptions ForwardURICompat , you told mod_jk to send the URI to Tomcat normally, which is less spec compliant but mod_rewrite compatible, use it for compatibility with Tomcat 3.2.x engines (on by default).

JkOptions ForwardURICompatUnparsed , the forwarded URI is unparsed, it's spec compliant but broke mod_rewrite.

JkOptions ForwardURIEscaped , the forwarded URI is escaped and Tomcat (since 3.3 rc2) will do the decoding part.

JkOptions ForwardDirectories is used in conjunction with DirectoryIndex directive of Apache web server. As such mod_dir should be available to Apache, statically or dynamically (DSO)

When DirectoryIndex is configured, Apache will create sub-requests for each of the local-url's specified in the directive, to determine if there is a local file that matches (this is done by stat-ing the file).

If ForwardDirectories is set to false (default) and Apache doesn't find any files that match, Apache will serve the content of the directory (if directive Options specifies Indexes for that directory) or a 403 Forbidden response (if directive Options doesn't specify Indexes for that directory).

If ForwarDirectories is set to true and Apache doesn't find any files that match, the request will be forwarded to Tomcat for resolution. This is used in cases when Apache cannot see the index files on the file system for various reasons: Tomcat is running on a different machine, the JSP file has been precompiled etc.

Note that locally visible files will take precedence over the ones visible only to Tomcat (i.e. if Apache can see the file, that's the one that's going to get served). This is important if there is more then one type of file that Tomcat normally serves - for instance Velocity pages and JSP pages.

The directive JkEnvVar allow you to forward an environment vars from Apache server to Tomcat engine.

Assigning URLs to Tomcat

If you have created a custom or local version of mod_jk.conf-local as noted above, you can change settings such as the workers or URL prefix.

JkMount directive assign specific URLs to Tomcat. In general the structure of a JkMount directive is:

You can use the JkMount directive at the top level or inside <VirtualHost> sections of your httpd.conf file.

Configuring Apache to serve static web application files

If the Tomcat Host appBase (webapps) directory is accessible by the Apache web server, Apache can be configured to serve web application context directory static files instead of passing the request to Tomcat.

Caution: If Apache is configured to serve static pages for a web application it bypasses any security contraints you may have configured in your web application web.xml config file.

Use Apache's Alias directive to map a single web application context directory into Apache's document space for a VirtualHost:

Use the mod_jk JkAutoAlias directive to map all web application context directories into Apache's document space.

Attempts to access the WEB-INF or META-INF directories within a web application context or a Web Archive *.war within the Tomcat Host appBase (webapps) directory will fail with an HTTP 403, Access Forbidden

Building mod_jk on Unix

The mod_jk build use the widely used configure system.

Prepare your mod_jk configure from CVS

To create jakarta-tomcat-connectors's autoconf script, you will need libtool 1.3.3 or higher, and autoconf 2.13 or newer.

Those tools will not be required if you are just using a package downloaded from apache.org, they are only required for developers.

To create the configure script just type :

Using configure to build mod_jk

Here's how to use configure to prepare mod_jk for building, just type:

./configure [autoconf arguments] [jakarta-tomcat-connectors arguments]

You could set CFLAGS and LDFLAGS to add some platform specifics:

If you want to build mod_jk for Apache 1.3 and 2.0, you should

• use configure and indicate Apache 1.3 apxs location (--with-apxs)
• use make
• copy the mod_jk binary to the apache modules location
• make clean (to remove all previously compiled modules)
• use configure and indicate Apache 2.0 apxs location,
• then make.

configure arguments

Examples of configure use

Building mod_jk for Apache on Windows NT/2K/XP

The module was developed using Visual C++ version 6.0, so having this environment is a prerequisite if you want to perform a custom build.

The steps that you need to take are:

• Change directory to the apache 1.3 or apache 2.0 source directory depending on your version of Apache.
• If you want to build mod_jk for Apache 1.3, set an APACHE1_HOME environment variable which points to where your Apache 1.3 is installed. A mod_jk module for Apache 2.0 build will require APACHE2_HOME environment variable to be set.
• Copy mod_jk.dll to Apache's modules directory.

An example on how to build mod_jk for Apache 1.3:

An example on how to build mod_jk for Apache 2.0:

If msdev is not in your path, enter the full path to msdev.exe. Also, ApacheCore.lib is expected to exist in the ${APACHEX_HOME}\src\CoreD and ${APACHEX_HOME}\src\CoreR directories before linking will succeed. You will need to build enough of the Apache source to create these libraries. This will build both release and debug versions of the redirector plug-in (mod_jk). An alternative will be to open mod_jk.dsp in msdev and build it using the build menu.

Building mod_jk for Apache on iSeries/OS400

Since OS400 V4R5, iSeries (AS/400) has used Apache 2.0 as their primary web server, replacing the old IBM webserver. It's now possible to build mod_jk on iSeries thanks to the help of the IBM Rochester Labs which has provided information and patches to adapt mod_jk to OS400.

You should have at least Apache 2.0.39, a C Compiler and IFS. Apache 2.0.39 is provided with the most recent set of PTFs for the iSeries Apache server, which can be found at http://www.ibm.com/servers/eserver/iseries/software/http/

To configure mod_jk on iSeries use the CL source provided with the mod_jk source.

• Get the latest mod_jk source and untar it on a Windows or Unix boxes
• Create a directory in IFS, ie /home/apache
• Send the whole jk source directory to iSeries directory via FTP.
• Then go to the iSeries command line :

In the edited file, specify that only jk_module should be exported :

You could start to build all the modules of mod_jk :

Next, you should restart your Apache 2.0 server and enjoy this piece of OpenSource on iSeries.

Getting mod_jk linked statically with Apache

mod_jk allows to install mod_jk in the Apache source tree to get a statically linked mod_jk. Having mod_jk in the httpd executable brings some performance improvements. The configure option --with-apache prepare mod_jk to install it in the Apache source tree. The option --with-apache works both for Apache-1.3 and Apache-2.0. The examples below show how to get mod_jk in the httpd process.

Installation in Apache-2.0

The enable-jk=share and enable-jk=static are not supported. --with-mod_jk only allow static linking of mod_jk.

Installation in Apache-1.3

The --enable-shared=jk is also working and builds a dso file.