Tomcat Netscape HowTo

By Gal Shachor <shachor@il.ibm.com>

This document explains how to set up Netscape web servers to cooperate with Tomcat. Normally the Netscape web servers come with their own Servlet engine, but you can also configure them to send servlet and JSP requests to Tomcat using the Tomcat redirector plugin.

Document Conventions and Assumptions

<tomcat_home> is the root directory of tomcat. Your Tomcat installation should have the following subdirectories:

1. <tomcat_home>\conf - Where you can place various configuration files
2. <tomcat_home>\webapps - Containing example applications
3. <tomcat_home>\bin - Where you place web server plugins

In all the examples in this document <tomcat_home> will be c:\jakarta-tomcat.

A worker is defined to be a tomcat process that accepts work from the Netscape server.

Supported Configuration

The Netscape-Tomcat redirector was developed and tested on:

1. WinNT4.0-i386 SP4/SP5/SP6a (it should be able to work on other versions of the NT service pack and also UNIX)
2. Netscape Enterprise 3.0 and 3.61
3. Tomcat3.0 - Tomcat3.2

The redirector uses ajp12 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.

Installation

As of Tomcat 3.2, a pre-built version of the Netscape redirector server plugin for Win32, nsapi_redirect.dll, is available under the win32/i386 directory where you downloaded the Tomcat binary distribution. For those using Netscape as your browser, try downloading a zip version of the file, if available. There can be problems using Netscape to download DLL files.

You can also build a copy locally from the source in Tomcat's source distribution.

The Tomcat redirector requires two entities:

1. nsapi_redirect.dll - The Netscape server plugin, either obtain a pre-built DLL or build it yourself (see the build section).
2. workers.properties - A file that describes the host(s) and port(s) used by the workers (Tomcat processes). This file is located in (tomcat/conf/workers.properties).

The installation includes the following parts:

1. Configuring the NSAPI redirector with a default /examples context and checking that you can serve servlets with Netscape.
2. Adding more contexts to the configuration.

Configuring the NSAPI Redirector

In this document I will assume that nsapi_redirect.dll is placed in c:\jakarta-tomcat\bin\win32\i386\nsapi_redirect.dll and that you created the properties files are in c:\jakarta-tomcat\conf.

1. If the Netscape built in servlet support is working disable it.
2. Add the redirector plugin into the Netscape server configuration. Edit your server obj.conf and add the following lines:
• In the Init section:
  Init fn="load-modules" funcs="jk_init,jk_service" shlib="d:/tomcat/bin/netscape/nt4/i386/nsapi_redirect.dll"
  Init fn="jk_init" worker_file="d:/tomcat/conf/workers.properties" log_level="debug" log_file="d:/tomcat/nsapi.log"
• In the default object NameTrans section
  NameTrans fn="assign-name" from="/servlet/*" name="servlet"
  NameTrans fn="assign-name" from="/examples/*" name="servlet"
• Create a new configuration object by adding the following lines to the end of the obj.conf file:
  <Object name=servlet>
  ObjectType fn=force-type type=text/plain
  Service fn="jk_service" worker="ajp12"
  </Object>
3. Restart Netscape (stop and start the server)

That's all, now you should start tomcat and ask Netscape for http://server:port/examples/

Adding additional Contexts

The examples context is useful for verifying your installation, but you will also need to add your own contexts. Adding a new context requires two operations:

1. Adding the context to Tomcat (I am not going to talk about this).
2. Assigning the NSAPI redirector to handle this context.

Assigning the NSAPI redirector to handle this context is simple, all you need to do is to edit obj.conf and add a NameTrans line that looks like:

NameTrans fn="assign-name" from="/<context name>/*" name="servlet"

After saving obj.conf restart Netscape and it will serve the new context.

As a new feature in Tomcat 3.2, a obj.conf-auto is automatically written each time Tomcat is started. This file includes settings for each of the contexts that Tomcat will serve during its run. Each context has settings to have Tomcat handle servlet and JSP requests, as well as a setting to have Netscape serve all other content. This file requires some modification before it can be used directly. If you wish to use this file directly, instead of copying some of its contents to another file, you should rename it (so it won't be overwritten the next time Tomcat is started) and make any required modifications.

Building the redirector

The redirector was developed using Visual C++ Ver.6.0, so having this environment is a prereq if you want to perform a custom build.

The steps that you need to take are:

1. Change directory to the nsapi plugins source directory.
2. Edit nsapi.dsp and update the include and library path to reflect your own Netscape server installation (search for a /I compiler option and /libpath linker option)
3. Execute the following command:
   MSDEV nsapi.dsp /MAKE ALL
   If msdev is not in your path, enter the full path to msdev.exe

This will build both release and debug versions of the redirector plugin.

An alternative will be to open the nsapi workspace file (nsapi.dsw) in msdev and build it using the build menu.

How does it work?

1. The Netscape-Tomcat redirector is an Netscape service step plugin, Netscape load the redirector plugin and calls its service handler function for request that are assigned to the "servlet" configuration object.
2. For each in-coming request Netscape will execute the set of NameTrans directives that we added to obj.conf, the assign-name function will check if it's from parameter matches the request URL.
3. If a match is found, assign-name will assign the servlet object name to the request. This will cause Netscape to send the request to the servlet configuration object.
4. Netscape will execute our jk_service extension. The extension collects the request parameters and forwards them to the appropriate worker using the ajp12 protocol (the worker="ajp12" parameter in jk_service inform it that the worker for this request is named ajp12).
5. The extension collects the response from the worker and returns it to the browser.

Advanced Context Configuration

Sometimes it is better to have Netscape serve the static pages (html, gif, jpeg etc.) even if these files are part of a context served by Tomcat. For example, consider the html and gif files in the examples context, there is no need to serve them from the Tomcat process, Netscape will suffice.

Making Netscape serve static files that are part of the Tomcat contexts requires the following:

1. Configuring Netscape to know about the Tomcat contexts
2. Make sure that the WEB-INF directory is protected from access.
3. Configuring Netscape to assign the NSAPI redirector only specific requests that requires JSP/Servlet handling.

Adding a Tomcat context to Netscape requires the addition of a new Netscape virtual directory that covers the Tomcat context. For example, adding a /example Netscape virtual directory that covers the c:\jakarta-tomcat\webapps\examples directory. To add a new virtual directory add the following line to your obj.conf:

NameTrans fn=pfx2dir from=/examples dir="c:/jakarta-tomcat/webapps/examples"

WEB-INF protection requires some explanation; Each servlet application (context) has a special directory named WEB-INF, this directory contains sensitive configurations data and Java classes and must be kept hidden from web users. WEB-INF can be protected by adding the following line to the PathCheck section in the default configuration object:

PathCheck fn="deny-existence" path="*/WEB-INF/*"

This line instructs the Netscape server to reject any request with a URL that contain the path /WEB-INF/.

Configuring Netscape to assign the NSAPI redirector only specific requests is somewhat harder, you will need to specify the exact URL-Path pattern(s) that you want Tomcat to handle (usually only JSP files and servlets). This requires a change to NemaTrans portion of obj.conf. For the examples context it requires to replace the following line:

NameTrans fn="assign-name" from="/examples/*" name="servlet"

with the following two lines:

NameTrans fn="assign-name" from="/examples/jsp/*.jsp" name="servlet"
NameTrans fn="assign-name" from="/examples/servlet/*" name="servlet"

As you can see the second configuration is more explicit, it actually instructs Netscape to assign the redirector with only requests to resources under /examples/servlet/ and resources under /examples/ whose name ends with .jsp. This is similar to what is automically written to the obj.conf-auto file for each context.

You can be even more explicit and provide lines such as:

NameTrans fn="assign-name" from="/examples/servletname" name="servlet"

that instructs Netscape to assign the redirector request whose URL-Path equals /example/servletname.

Advanced Worker Configuration

Sometimes you want to serve different contexts with different Tomcat processes (for example to spread the load among different machines). To achieve such goal you will need to define several workers and assign each context with its own worker.

Defining workers is done in workers.properties, this file includes two types of entries:

1. An entry that lists all the workers defined. For example:
   worker.list=ajp12, ajp12second
2. Entries that define the host and port associated with these workers. For example:
   worker.ajp12.host=localhost
   worker.ajp12.port=8007
   worker.ajp12second.host=otherhost
   worker.ajp12second.port=8007

The above examples defined two workers, now we can use these workers to serve two different contexts each with it’s own worker. Submitting requests to different workers is accomplished by using multiple Service directives in the servlet configuration Object, each with a different path pattern parameter. For example, if we want to submit the /servlet context to a worker named ajp12 and the /examples context to a worker named ajp12second we should use the following configuration:

<Object name=servlet>
ObjectType fn=force-type type=text/plain
Service fn="jk_service" worker="ajp12" path="/servlet/*"
Service fn="jk_service" worker="ajp12second" path="/examples/*"
Service fn="jk_service" worker="ajp12"
</Object>

Feedback

Please send feedback, bug report or any additional information to tomcat-user@jakarta.apache.org.