FAQ/Connectors

Preface

Please see the Other Resources Link for other pages describing how they were able to link Tomcat with a connector. With luck, someone documented their experience in an environment which is similar to yours.

Here is a link to the JK Connectors. It contains more configuration and installation information.

Please note, jk2 is no longer supported. Please use mod_jk instead.

Questions

1. What is JK (or AJP)?

2. Which connector: mod_jserv, JK, JK2, mod_webapp or mod_proxy?

3. Why should I integrate Apache with Tomcat? (or not)

4. At boot, is order of start up (Apache vs Tomcat) important?

5. Is there any way to control the content of automatically generated mod_jk.conf-auto?

6. How do I bind to a specific ip address?

7. Where can I download a binary distribution of my connector?

8. I'm having strange UTF-8 issues with my request parameters.

Answers

What is JK (or AJP)?

AJP is a wire protocol. It an optimized version of the HTTP protocol to allow a standalone web server such as Apache talk to Tomcat. Historically, Apache has always been much faster than Tomcat at serving static content. The idea is to let Apache serve the static content when possible, then proxy the request back to Tomcat for Tomcat related content.

Which connector: mod_jserv, JK, JK2, mod_webapp or mod_proxy?

• Stay away from mod_webapp, aka warp. It is deprecated and unsupported due to lack of developer interest and there are better options such as jk and mod_proxy. It WILL NOT run on windows. Do not use mod_webapp or warp.

• mod_jserv is unsupported and will not be supported in Tomcat 5. mod_jserv was the original connector which supported the ajp protocol. Do not use mod_jserv.

• jk2 is a refactoring of mod_jk and uses the Apache Portable Runtime (apr). But due to lack of developer interest, it is unsupported. The alternative is mod_jk or mod_proxy_ajp. Do not use jk2.

• mod_jk is great and should be used for production. It is still under active development and also works for the apache 2.X series for cases where you do not want to use mod_proxy_ajp.

• mod_proxy. A cheap way to proxy without the hassles of configuring JK. This solution lacks sticky session load balancing. If you don't need some of the features of jk - this is a very simple alternative.

• mod_proxy_ajp. With apache 2.2, mod_proxy was rewritten to support load balancing as well as a new transport called mod_proxy_ajp. This module is distributed with the Apache http server, not the Tomcat server.

Why should I integrate Apache with Tomcat? (or not)

There are many reasons to integrate Tomcat with Apache. And there are reasons why it should not be done too. Needless to say, everyone will disagree with the opinions here. With the performance of Tomcat 5 and 6, performance reasons become harder to justify. So here are the issues to discuss in integrating vs not.

• Clustering. By using Apache as a front end you can let Apache act as a front door to your content to multiple Tomcat instances. If one of your Tomcats fails, Apache ignores it and your Sysadmin can sleep through the night. This point could be ignored if you use a hardware loadbalancer and Tomcat's clustering capabilities.

• Clustering/Security. You can also use Apache as a front door to different Tomcats for different URL namespaces (/app1/, /app2/, /app3/, or virtual hosts). The Tomcats can then be each in a protected area and from a security point of view, you only need to worry about the Apache server. Essentially, Apache becomes a smart proxy server.

• Security. This topic can sway one either way. Java has the security manager while Apache has a larger mindshare and more tricks with respect to security. I won't go into this in more detail, but let Google be your friend. Depending on your scenario, one might be better than the other. But also keep in mind, if you run Apache with Tomcat - you have two systems to defend, not one.

• Add-ons. Adding on CGI, perl, PHP is very natural to Apache. Its slower and more of a kludge for Tomcat. Apache also has hundreds of modules that can be plugged in at will. Tomcat can have this ability, but the code hasn't been written yet.

• Decorators! With Apache in front of Tomcat, you can perform any number of decorators that Tomcat doesn't support or doesn't have the immediate code support. For example, mod_headers, mod_rewrite, and mod_alias could be written for Tomcat, but why reinvent the wheel when Apache has done it so well?

• Speed. Apache is faster at serving static content than Tomcat. But unless you have a high traffic site, this point is useless. But in some scenarios, tomcat can be faster than Apache httpd. So benchmark YOUR site. Tomcat can perform at httpd speeds when using the proper connector (APR with sendFile enabled). Speed should not be considered a factor when choosing between Apache httpd and Tomcat

• Socket handling/system stability. Apache has better socket handling with respect to error conditions than Tomcat. The main reason is Tomcat must perform all its socket handling via the JVM which needs to be cross platform. The problem is socket optimization is a platform specific ordeal. Most of the time the java code is fine, but when you are also bombarded with dropped connections, invalid packets, invalid requests from invalid IP's, Apache does a better job at dropping these error conditions than JVM based program. (YMMV)

At boot, is order of start up (Apache vs Tomcat) important?

No. This way - either apache or tomcat can be restarted at any time independent of one another.

Is there any way to control the content of automatically generated mod_jk.conf-auto? I need my own specific commands added to it.

There really is no need to. Just copy the automatically generated mod_jk.conf-auto and edit it manually to your preference. None of production tomcat installations really use mod_jk.conf-auto as it is.

How do I bind to a specific ip address?

Each Connector element allows an address property. For example:

<Connector className="org.apache.coyote.tomcat4.CoyoteConnector" 
           address="192.168.1.1"
           port="8080" minProcessors="5" maxProcessors="75"
           enableLookups="true" redirectPort="8443"
           acceptCount="100" debug="0" connectionTimeout="20000"
           useURIValidationHack="false" disableUploadTimeout="true" />

For a more complete description of the Connector config, see the HTTP Connector docs or the see the AJP Connector docs.

Where can I download a binary distribution of my connector?

You can't: you need to download the source and compile it for your platform. The source distributions are available from the standard location. Note that JPackage.org has RPM distributions for the connectors as well as tomcat itself: JPackage.org

I'm having strange UTF-8 issues with my request parameters.

See Character Encoding