The Jakarta Project Tomcat FAQ

Tomcat FAQ

Connectors

Preface

Many people have also documented getting the connectors to work in their own environment. Each person had their own situation to deal with. Hopefully your situation matches one of theirs. Otherwise, we also do provide the reference documentation.

Questions

Answers
What is JK?
JK 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 jk2. It is WILL NOT run on windows.
  • mod_jserv is good but AFAIK is unsupported and will not be supported in Tomcat 5.
  • mod_jk is great and should be used for production. It is getting fixes as needed (which is now rare).
  • jk2 is a refactoring of mod_jk and uses the Apache Portable Runtime (apr). If you are using Apache 2.0, you'll probably want to use jk2. But this may not be production worthy for everyone. (YMMV)
  • mod_proxy. Interesting idea and it doesn't seem to have much problems with heavy loads. If you don't need some of the features of jk, jk2 - this is a very simple alternative.

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 upcoming performance of Tomcat 5, 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.
  • 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.
  • Here is a great response from Craig R. McClanahan. If you have free time, read emails by him in any of the list archives. You'll learn a lot.

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.

JK2 doesn't seem to be using my settings in my workers2.properties file such as creating the shm file or mapping the URIs listed to Tomcat, what's wrong?
JK2 is not finding your workers2.properties file. Specify it's location in your httpd.conf file by adding:

JkSet config.file /full/system/path/to/workers2.properties

Thread which spawned this question.

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" />

Copyright © 1999-2003, Apache Software Foundation