FAQ
Author: Henri Gomez

Apache Software Foundation | Jakarta Project | Apache Tomcat
General
General Informations and FAQ about JK
Where can I get help/support for JK ?
The primary mechanism for support is through the JK documentation included in the doc directory. Documentation is also available on the Apache Jakarta web site devoted to the Jakarta Tomcat Connectors Project For additional help, the best resource is the Tomcat Users Discussion list. You should start by searching the mail list archive before you post questions to the list. If you are unable to locate the answer to your question in the archive, you can post questions about JK to the user list for assistance. Make sure that you include the version of your Webserver, that you are using as well as the platform you are running on and go here to determine how to subscribe to tomcat mailing list.
I can't find JK anywhere. Where is it?
Now that JK moved to the jakarta-tomcat-connectors repository, the source and binaries for JK are present in the jakarta-tomcat-connectors directory
What's the difference between JK and mod_jk ?
JK is a project covering web-servers to Tomcat connectors, whereas mod_jk is the Apache module developped in JK. Domino webserver support is implemented on JK, using a redirector called dsapi redirector . IIS webserver support is implemented on JK, using a redirector called isapi redirector . Netscape/iPlanet webserver webserver support is implemented on JK, using a redirector called nsapi redirector .
Where can I get more information ?
For JK 1.2.x , you should read : For the impatients Apache and JK Domino and JK IIS and JK Netscape/iPlanet and JK Workers configuration For JK 2.0.x the config tomcat and config webserver documents have considerably more in-depth information. It's worth a look. You could also try searching the mailing list archives for "JK" or look at the source.
Which protocol should I use? Ajp12 or Ajp13?
Ajp13 is a newer protocol, it's faster, and it works better with SSL. You almost certainly want to use it now that ajp12 is deprecated. Also ajp13 is supported by all Apache Tomcat including 3.2.x , 3.3.x, 4.0.x, 4.1.x and the new tomcat 5. Others Servlet engines like jetty have support for Ajp13.
I've got a firewall between my WebServer and Tomcat who drop ajp13 connections after some times
Ajp13 use persistant connections where the traffic could be null if there is no request to be sent to Tomcat. Firewall used to drop inactive connections and will make your WebServer and Tomcat think the connection is valid. Starting with JK 1.2.0, a socket_keepalive property as been added to ajp13 settings, and you should take a look at it in Workers HowTo .
Under heavy load, I've got many threads in Tomcat even if my Apache Web Server handle much of the load
Under heavy load, Apache WebServer create many childs to handle the load, which will in turn create many connections to Tomcat to forward the requests they should handle. Apache WebServer will normally kill the childs/threads when the load decrease. But if the load is still there and even if only Apache handle the requests, ie static contents, the childs are kept and with them the ajp13 connections, even if they are no more used. Since JK 1.2.0, cache_timeout and socket_timeout properties as been added to close connections after some time of inactivity, for more informations refer to Workers HowTo .
Apache
Informations and FAQ about mod_jk and Apache Web Servers.
Whenever I restart Tomcat, Apache locks up!
The Ajp13 protocol keeps an open socket between Tomcat and Apache. Release of mod_jk present in J-T-C handle the network failure. But with previous release of mod_jk, you may have to restart Apache as well.
Why did exist two files mod_jk.so (-eapi ad -noeapi) in download dir for Linux ?
Many versions of Apache use of modified API, known at Extended API, developped for use with the mod_ssl module . For example, Apache present in certains recent Linux distributions include the mod_ssl module. So if you got such 'Extended Apache', you need to use mod_jk.so-eapi . You should use mod_jk.so-noeapi only for 'Standard Apache' (ie without mod_ssl). It's wise to avoid using EAPI modules on STD API Apache or to use standard API modules on EAPI Apache. Allways be sure to have the mod_jk.so witch match your version of Apache
What's that message about 'garbled DSO ?'
It's related to Apache EAPI, the message 'mod_jk.so is garbled - perhaps this is not an Apache module DSO ?' just told you, that your're trying to install a mod_jk.so DSO module that was compiled on an Apache using EAPI, like apache-mod_ssl or apache from Redhat distro 6.2/7.0 but your system use the standard apache with normal API.
And the message about 'module might crash under EAPI!
Also related to EAPI, the message '[warn] Loaded DSO /usr/lib/apache/mod_jk.so uses plain Apache 1.3 API, this module might crash under EAPI! (please recompile it with -DEAPI)', the mod_jk.so was compiled under normal Apache with standard API and you try to install the module on an Apache using EAPI.
APXS is getting an error during the build of mod_jk, like rc=0 or rc=255. I tried all of the steps in the build section, what do I do now ?
APXS is a Perl script that is created when you build the Apache web server from source. Chances are that if you are getting these errors and you obtained Apache as a binary distribution, that APXS is not configured correctly for your system. Your best bet is to get the Apache source from http://httpd.apache.org and build it yourself. Use the following for a basic build (read the Apache docs for other options):
`[user@host] ~ $ cd /usr/local/src` `[user@host] ~ $ gzip -dc apache_1.3.19.tar.gz|tar xvf -` `[user@host] ~ $ cd apache_1.3.19` `[user@host] ~ $ ./configure --prefix=/usr/local/apache \` `[user@host] ~ $ --enable-module=most \` `[user@host] ~ $ --enable-shared=max` `[user@host] ~ $ make` `[user@host] ~ $ make install`
Note: The above steps assume that you downloaded the Apache source and placed it in your /usr/local/src directory.
Apache 2.0 complains about incorrect module version
Since Apache 2.0 API still change often, the Apache 2.0 teams decide to put in headers of compiled modules the Apache 2.0 version used to compile the module. This check is called Magic Module Number bump. At start time Apache 2.0 check that version in modules headers and stop if it detect that a module was compiled for another Apache 2.0 version. As such you should allways use modules compiled for the same Apache 2.0 version. This check may be removed if the future.
JNI didn't works with Apache 1.3
JNI support require a multi-threaded environment which is not the general case for Apache 1.3. You should verify if Apache 1.3 has been build with thread support and if not you could add the the pthreads library to your httpd.conf file.
# Add pthread to Apache in httpd.conf `LoadModule "/usr/lib/libpthreads.so"`
Also keep in mind that JNI is suited for multi-threaded servers and you should consider upgrading to Apache 2.0 to support JNI.
JNI report that JVM couldn't be started under Linux
Under Linux, you should set some environment variables BEFORE launching your Apache server :
`export LD_LIBRARY_PATH=$jre/bin:$jre/bin/classic:$LD_LIBRARY_PATH`
Also some Linux distributions have enabled a GLIBC feature called 'floating stacks' which may not works with kernel less than 2.4.10 on SMP machines. You should disable floating stacks by exporting an environment variable :
`export LD_ASSUME_KERNEL=2.2.5`
You could have to update your service scripts, ie /etc/rc.d/init.d/httpd , to set these env vars before your httpd server starts.
Mixed errors when building via configure
configure assume you have some GNU tools allready installed and configured for your system, and ad minima libtool . Also some systems may have mixed cc and gcc setup which may make you puzzled when trying to link an Apache built with native c compiler with a jk/jk2 build with gcc. In fine some native make didn't works as expect so you should use a GNU make gmake .
JK2 build report error about missing FIONBIO on Solaris 8
In JK2 before v2.0.2, you should add
    #define BSD_COMP
in top of jk/native2/common/jk_channel_socket.c to have Solaris build succeed.
IIS
Informations and FAQ about JK and IIS Web Servers. This paragraph has not been written yet, but you can contribute to it.
NES/iPlanet
Informations and FAQ about JK and NES/iPlanet Web Servers. This paragraph has not been written yet, but you can contribute to it.