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Sample answer: if you will serv only static content and/or php you need Apache web server, if you need java application server/servlet container you need Tomcat. If you will use Tomcat for something more that testing/very light load its wise to put in front Apache web server and use specific plugin for serving requests to Tomcat. There are many ways to compare Tomcat vs. The Apache HTTP Server, but the fundamental difference is that Tomcat provides dynamic content by employing Java-based logic, while the Apache web server's primary purpose is to simply serve up static content such as HTML, images, audio and text. Apache is a popular open-source, cross-platform web server that is, by the numbers, the most popular web server in existence. It’s actively maintained by the Apache Software Foundation. Some high-profile companies using Apache include Cisco, IBM, Salesforce, General Electric, Adobe, VMware, Xerox, LinkedIn, Facebook, Hewlett-Packard, AT&T.
Apache HTTP Server HowTo
Introduction
This document explains how to connect Tomcat to the popular open source web server, Apache HTTP Server.You can use the connection module mod_jk with any version of Apache starting with 1.3 and any versionof Tomcat starting with (at least) 3.2.
It is recommended that you also read theWorkers HowTo documentto learn how to setup the working entities between your web server and Tomcat Engines.For more detailed configuration information consult the Reference Guide forworkers.properties,uriworkermapand Apache.
Warning: If Apache and Tomcat are configured to serve content fromthe same file system location then care must be taken to ensure that Apache isnot able to serve inappropriate content such as the contents of the WEB-INFdirectory or JSP source code. This could occur if the Apache DocumentRootoverlaps with a Tomcat Host's appBase or the docBase of any Context. It couldalso occur when using the Apache Alias directive with a Tomcat Host's appBase orthe docBase of any Context.
This document was originally part of Tomcat: A Minimalistic User's Guide written by Gal Shachor,but has been split off for organisational 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, Solaris and should work on major Unixes platformssupporting Apache 1.3 and/or 2.x
- 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)
- i5/OS V5R4 (System I) with Apache HTTP Server 2.0.58. Be sure to have the latest Apache PTF installed.
- Tomcat 3.2 to Tomcat 8.
The mod_jk module uses the AJP protocol to send requests to the Tomcat containers.The AJP version typically used is ajp13.
Who supports AJP protocols?
Tomcat supports ajp13 since Tomcat 3.2.Others servlet engines such as Jetty or JBoss also support the ajp13 protocol
The ajp12 protocol has been deprecated and you should no longer use it.The ajp14 protocol is considered experimental.
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 therequests by providing the necessary content.
Adding a servlet container may somewhat change this behaviour.Now the web server needs also to perform the following:
- Load the servlet container adaptor library and initialise 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 adaptor take the request and handle it.
The adaptor 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 serverbut on different servlet container JVMs.We will cover these two cases in the advanced sections.
Obtaining mod_jk
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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 instructionsgiven in the below 'Building mod_jk' sections for building mod_jk from source.The mod_jk source can be downloaded from a mirrorhere
The binaries for mod_jk are now available for several platforms.The binaries are located in subdirectories by platform.
For some platforms, such as Windows, this is the typical way of obtaining mod_jksince most Windows systems do not have C compilers.
For others, the binary distribution of mod_jk offers simpler installation.
For example JK 1.2.x can be downloaded from a mirrorhere (look for JK 1.2 Binary Releases). The 'JK 1.2 Binary Releases' link contains binary version for a variety ofoperating systems for both Apache 1.3 and Apache 2.x.
Installation
mod_jk requires two entities:
- mod_jk.xxx - The Apache HTTP Server module, depending on your operating system, it will be mod_jk.so, mod_jk.nlmor MOD_JK.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 in the source download.
Also as with other Apache modules, mod_jk should be first installed on the modules directory of yourApache HTTP Server, 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 directivesfrom 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 auto-configure works only for a single Tomcat running on the same machine where the Apache HTTP Server is running.The simplest way to configure Apache HTTP Server to use mod_jk is to turn on the Apache HTTP Server auto-configure settingin 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:
Note: this file may also be generated as $TOMCAT_HOME/conf/auto/mod_jk.conf
This will tell the Apache HTTP Server to use directives in the mod_jk.conf-auto file inthe Apache configuration. This file is created by enabling the Apacheauto-configuration by creating your workers.properties file at$TOMCAT_HOME/conf/jk/workers.properties and adding the listener to the Engineelement in the server.xml file as per the following example.Please note that this example is specific to Tomcat 5.x, unlike other sections of this document which also apply to previous Tomcat branches.
Then restart Tomcat and mod_jk.conf should be generated. For more information onthis topic, please refer to the API documentation at theTomcat docs website.
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 web server,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 different Tomcat engines,each one having it's own configuration, a general case in ISP hosting
- Also most Apache web masters will retain custom configuration to be able to tune the settingsto 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.
Since JK 1.2.3 for Apache 2.x and JK 1.2.16 for Apache 1.3 this can alsobe used for piped logging:
JkLogLevelset 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 information 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.See the mod_jk Apache HTTP Server reference for details.
You can log mod_jk information using the Apache standard module mod_log_config.The module sets several notes in the Apache notes table.Most of them are are only useful in combination with a load balancer worker.See the mod_jk Apache HTTP Server reference for details.
You can also log a request protocol in the mod_jk log file instead ofthe access log. This is not recommended and mostly a backward compatibilityfeature. The directive JkRequestLogFormat will configure the formatof this protocol. It gets configured and enabled on a per virtual host basis.See the mod_jk Apache HTTP Server reference for details.
Forwarding
The directive JkOptions allow you to set many forwarding options which will enable (+)or disable (-) following option. Without any leading signs, options will be enabled.
The four following options +ForwardURIxxx are mutually exclusive.Exactly one of them is required, a negative sign prefix is not allowed with them.The default value is 'ForwardURIProxy' since version 1.2.24.It was 'ForwardURICompatUnparsed' in version 1.2.23 and'ForwardURICompat' until version 1.2.22.You can turn the default off by switching on one of the other two options.You should leave this at it's default value, unless you have a very goodreason to change it.
All options are inherited from the global server to virtual hosts.Options that support enabling (plus options) and disabling (minus options),are inherited in the following way:
options(vhost) = plus_options(global) - minus_options(global) + plus_options(vhost) - minus_options(vhost)
Using JkOptions ForwardURIProxy, the forwarded URIwill be partially reencoded after processing inside Apache andbefore forwarding to Tomcat. This will be compatible with localURL manipulation by mod_rewrite and with URL encoded session ids.
Using JkOptions ForwardURICompatUnparsed, the forwarded URIwill be unparsed. It's spec compliant and secure.It will always forward the original request URI, so rewritingURIs with mod_rewrite and then forwarding the rewritten URIwill not work.
Using JkOptions ForwardURICompat, the forwarded URI willbe decoded by Apache. Encoded characters will be decoded andexplicit path components like '..' will already be resolved.This is less spec compliant and is not safe if you are usingprefix JkMount. This option will allow to rewrite URIs withmod_rewrite before forwarding.
Using JkOptions ForwardURIEscaped, the forwarded URI willbe the encoded form of the URI used by ForwardURICompat.Explicit path components like '..' will already be resolved.This will not work in combination with URL encoded session IDs,but it will allow to rewrite URIs with mod_rewrite before forwarding.
JkOptions RejectUnsafeURI will block allURLs, which contain percent signs '%' or backslashes 'after decoding.
Most web apps do not use such URLs. Using the option RejectUnsafeURI, youcan block several well known URL encoding attacks. By default, this optionis not set.
You can also realise such a check with mod_rewrite, which is more powerfulbut also slightly more complicated.
JkOptions CollapseSlashesAll is deprecated as of 1.2.44 and will beignored if used.
JkOptions CollapseSlashesUnmount is deprecated as of 1.2.44 and will beignored if used.
JkOptions CollapseSlashesNone is deprecated as of 1.2.44 and will beignored if used.
JkOptions ForwardDirectories is used in conjunction with DirectoryIndexdirective of Apache. As such mod_dir should be available to Apache,statically or dynamically (DSO)
When DirectoryIndex is configured, Apache will create sub-requests foreach of the local-url's specified in the directive, to determine if there is alocal file that matches (this is done by stat-ing the file).
If ForwardDirectories is set to false (default) and Apache doesn't find anyfiles that match, Apache will serve the content of the directory (if directiveOptions specifies Indexes for that directory) or a 403 Forbidden response (ifdirective Options doesn't specify Indexes for that directory).
If ForwardDirectories is set to true and Apache doesn't find any files thatmatch, the request will be forwarded to Tomcat for resolution. This is used incases when Apache cannot see the index files on the file system for variousreasons: Tomcat is running on a different machine, the JSP file has beenprecompiled etc.
Note that locally visible files will take precedence over theones visible only to Tomcat (i.e. if Apache can see the file, that's the onethat's going to get served). This is important if there is more then one type offile that Tomcat normally serves - for instance Velocity pages and JSP pages.
Setting JkOptions ForwardLocalAddress, you ask mod_jk to send the local addressof the Apache HTTP Server instead of remote client address. This can be used byTomcat remote address valve for allowing connections only from configured Apacheservers.
Setting JkOptions ForwardPhysicalAddress, you ask mod_jk to send thephysical peer TCP IP address as the client address. By default mod_jkuses the logical address as provided by the web server. For example the modulemod_remoteip sets the logical IP address to the client IP forwarded by proxiesin the X-Forwarded-For header.
JkOptions FlushPackets, you ask mod_jk to flush Apache's connectionbuffer after each AJP packet chunk received from Tomcat. This option can havea strong performance penalty for Apache and Tomcat as writes are performedmore often than would normally be required (ie: at the end of eachresponse).
JkOptions FlushHeader, you ask mod_jk to flush Apache's connectionbuffer after the response headers have been received from Tomcat.
JkOptions DisableReuse, you ask mod_jk to close connections immediatelyafter their use. Normally mod_jk uses persistent connections and pools idleconnections to reuse them, when new requests have to be sent to Tomcat.
Using this option will have a strong performance penalty for Apache and Tomcat.Use this only as a last resort in case of unfixable network problems.If a firewall between Apache and Tomcat silently kills idle connections,try to use the worker attribute socket_keepalive in combination with an appropriateTCP keepalive value in your OS.
JkOptions ForwardKeySize, you ask mod_jk, when using ajp13, to forward also the SSL Key Size asrequired by Servlet API 2.3.This flag shouldn't be set when servlet engine is Tomcat 3.2.x (off by default).
JkOptions ForwardSSLCertChain, you ask mod_jk, when using ajp13,to forward SSL certificate chain (off by default).Mod_jk only passes the SSL_CLIENT_CERT to the AJP connector. This is not aproblem with self-signed certificates or certificates directly signed by theroot CA certificate. However, there's a large number of certificates signed byan intermediate CA certificate, where this is a significant problem: A servletwill not have the possibility to validate the client certificate on its own. Thebug would be fixed by passing on the SSL_CLIENT_CERT_CHAIN to Tomcat via the AJP connector.
This directive exists only since version 1.2.22.
The directive JkEnvVar allows you to forward environment variablesfrom Apache server to Tomcat engine.You can add a default value as a second parameter to the directive.If the default value is not given explicitly, the variablewill only be send, if it is set during runtime.
The variables can be retrieved on the Tomcat side as request attributesvia request.getAttribute(attributeName).Note that the variables send via JkEnvVar will not be listedin request.getAttributeNames().
The variables are inherited from the global server to virtual hosts.
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 HTTP Server,Apache can be configured to serve web application context directory static files insteadof passing the request to Tomcat.
Caution: For security reasons it is strongly recommended that JkMount is used topass all requests to Tomcat by default and JkUnMount is used to explicitlyexclude static content to be served by Apache. It should also be noted thatcontent served by Apache will bypass any security constraints defined in theapplication's web.xml.
Use Apache's Alias directive to map a single web application context directory into Apache'sdocument space for a VirtualHost:
Starting with mod_jk 1.2.6 for Apache 2.x and 1.2.19 for Apache 1.3, it's possible to exclude some URL/URI fromjk processing by setting the env var no-jk, for example with the SetEnvIf Directive.
You could use no-jk env var to fix problem with mod_alias or mod_userdirdirective when jk and alias/userdir URLs matches.
Use the mod_jk JkAutoAlias directive to map all web application context directoriesinto Apache's document space.
Attempts to access the WEB-INF or META-INF directories within a web application contextor a Web Archive *.war within the Tomcat Host appBase (webapps) directory will fail with anHTTP 403, Access Forbidden
If you encoded all your URLs to contain the session id(;jsessionid=...), and you later decide, you want tomove part of the content to Apache, you can tellmod_jk to strip off all session ids from URLs forthose requests, that do not get forwarded via mod_jk.
You enable this feature by setting JkStripSession to On.It can be enabled individually for virtual servers. The defaultvalue is Off.
Building mod_jk on Unix
The mod_jk build use the widely used configure system.
Prepare your mod_jk configure from subversion
In case you get source from subversion, ie without an existing configure script,you should have autoconf for configuration and installation.To create the mod_jk autoconf script, you will need libtool1.5.2, automake 1.10 and autoconf 2.59 or newer. The use of more recentversions is encouraged, e.g. for reliable detection of the features ofrecent version of operating systems.
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
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Here's how to use configure to prepare mod_jk for building, just type:
You could set CFLAGS and LDFLAGS to add some platform specifics:
If you want to build mod_jk for different versions of the Apache HTTP Server, like 1.3 or 2.x,you need to go through the full build process for each of them.Please note, that Apache 2.0, 2.2 or 2.4 modules are not binary compatible.You have to compile the module using the Apache version you plan to run it in.The mod_jk build directory used is 'apache-2.0' for all 2.x builds. The source codeis compatible with Apache HTTP Server 2.0, 2.2 and 2.4.
- use configure and indicate the correct Apache HTTP Server apxs location (--with-apxs)
- use make
- copy the resulting mod_jk.so binary from the apache-1.3 or apache-2.0 subdirectoryto the Apache HTTP Server modules location.
- make clean (to remove all previously compiled object files)
- Start over with the apxs location for your next Apache HTTP Server version.
configure arguments
| Apache related parameters | |
|---|---|
| --with-apxs[=FILE] | FILE is the location of the apxs tool. Default is finding apxs in PATH.It builds a shared Apache module. It detects automatically the Apache version.(2.x and 1.3) |
| --with-apache=DIR | DIR is the path where Apache sources are located.The Apache sources should have been configured before configuring mod_jk.DIR is something like: /home/apache/apache_1.3.19It builds a static Apache module. |
| --enable-EAPI | This parameter is needed when using Apache-1.3 and mod_ssl, otherwise you will get the error message:'this module might crash under EAPI!' when loading mod_jk.so in Apache.Not needed when --with-apxs has been used |
| --enable-prefork | In case you build mod_jk for a multi-threaded Apache HTTP Server 2.x MPM (Multi-Processing Module),some areas of mod_jk code need to be synchronised to make it thread-safe.Because configure can not easily detect, whether your are using a multi-threaded MPM,mod_jk by default is always build thread-safe for Apache HTTP Server 2.x.If you are sure, that your MPM is not multi-threaded, you can use '--enable-prefork'to force the removal of the synchronisation code (thus increasing performance a bit).For instance, the prefork MPM is not multi-threaded. For Apache HTTP Server 1.3this flag will be set automatically. |
| --disable-trace | When using log level 'trace', mod_jk traces a lot of function calls with'enter' and 'exit' log messages. Even if the log level is not 'trace',comparing the log levels to decide about logging has some performanceimpact. If you use '--disable-trace', then the trace log code doesn't get compiledinto the module binary and you might save some cycles during execution. Even with '--disable-trace' logging debug messages with debug log levelwill still be possible. |
| --enable-api-compatibility | Only use Apache API functions available in all Apache production releasesof the chosen major Apache release branch. This improves binarycompatibility of module builds with Apache releases older than the releaseagainst mod_jk is build (only between minor Apache versions). |
| --enable-flock | In case the operating system supports flock system call use this flag to enable thisfaster locks that are implemented as system call instead emulated by GNU C library. However those locks does not work on NFS mounted volumes, so you can use'--enable-flock' during compile time to force the flocks() calls. |
Examples of configure use
Building mod_jk for Apache on Windows
The module was developed using Microsoft Visual C++, so having Visual Studio installedis a prerequisite if you want to perform your own build.
You can build the source using the IDE GUI, or using a purecommandline build based on nmake. The IDE build currently onlysupports building 32 Bit binaries. The nmake builds are availablefor 32 Bit and 64 Bit binaries.
The common steps for all build procedures are:
- Set up your build environment for 32 Bits or 64 Bits.The IDE build only supports 32 Bits.
- Download the sources as a zip file and unpack it.
- Change directory to the ISAPI redirector source directory.
- Set your path to the Apache web server directory in yourenvironment.
The steps for an IDE build are then:
- Start Visual Studio using 'start mod_jk.dsp'
- During IDE startup choose 'Yes' in all conversion popups.
- Next choose a Configuration form the dropdown. There are pre-definedconfigurations for debug and release builds and in the'apache-2.0' directory each of them is available as a configurationto build against the web server versions 2.0, 2.2 and 2.4.
- Finally choose 'Build Solution' in the 'Build' menu.
Alternatively the steps for an nmake commandline build are:
- Set your target architecture to X86 or X64 by editing the 'ARCH='line in the file Makefile.vc.
- Issue 'nmake -f Makefile.vc'
Finally you need to copy the file mod_jk.so to the modules directoryof your Apache HTTP server (resp. the libexec directory for the old Apache 1.3).
For Apache HTTP Server 1.3, ApacheCore.lib is expected to exist beforelinking mod_jk will succeed.
Building mod_jk for Apache on System I - i5/OS (OS400)
Since OS400 V4R5, System I (AS/400) has used Apache 2.0 as their primary web server,replacing the old IBM web server.It's now possible to build mod_jk on System I thanks to the help of the IBMRochester Labs which has provided information and patches to adapt mod_jk to i5/OS.
You should have at least Apache 2.0.58 (product 5722DG1), a C Compiler and IFS.Apache 2.0.58 is provided with the most recent set of PTFs for the iSeries Apacheserver, which can be found at http://www.ibm.com/servers/eserver/iseries/software/http/
The all latest Apache 2 for i5/OS V5R3 (or V5R4) is now 2.0.58 (as of 2007/04/17).Be sure to have the latest PTFs loaded if you want to make use of jk 1.2.15 and higher.NB: The latest mod_jk known to work on i5/OS V5R3 was 1.2.19.
New in i5/OS V5R4, UTF is required, also for Apache modules, as such Apache modules do not requiretranslations to/from EBCDIC but works should be done to port mod_jk 1.2.23 (and higher) to V5R4.From the V5R4 Infocenter:As of i5/OS(tm) V5R4, modules must be recompiled with a UTF locale. This creates an environment where locale-dependent C runtime functions assumethat string data is encoded in UTF-8. Any hardcoded constants can be encoded in UTF-8 by adding a #pragma convert(1208) statement in the module.Additionally, input data from the client will no longer be converted to EBCDIC but will be passed as-is.Output data sent from the module is not converted either so it must be encoded in ASCII or UTF8 as required.APR and HTTP APIs as of V5R4, expect data in UTF-8. Note that several APIs have additional functions that allow a CCSID to be set toindicate the encoding of the parameters being passed. Conversion functions between UTF-8 and EBCDIC have been added.Be sure to review APIs used by your module to be aware of current changes.
To configure mod_jk on System I 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 System I directory via FTP.
- Then go to the System I 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 (cases for V5R4 or previous releases):
Next, you should restart your Apache 2.0 instance and enjoy this piece of OpenSource on System I.
Building mod_jk for Apache on MacOS/X
Mac OS X (10.2.x) build notes:
Assuming that you are root:
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Getting mod_jk linked statically with Apache
mod_jk allows to install mod_jk in the Apache source tree to get a staticallylinked mod_jk. Having mod_jk in the Apache executable brings some small performanceimprovements. The configure option --with-apache prepare mod_jk to install itin the Apache source tree.The option --with-apache works both for Apache 1.3 and Apache 2.x.The examples below show how to get mod_jk in the Apache process.
Installation for Apache-2.x
The enable-jk=share and enable-jk=static are not supported. --with-mod_jk onlyallow static linking of mod_jk.
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Installation for Apache-1.3
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The --enable-shared=jk is also working and builds a dso file.
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