Configuring AJP13 Using mod_jk or mod_proxy_ajp

The apache web server is frequently used as a server in front of a servlet container.
While there are no real technical reasons to front Jetty with apache, sometimes this is needed
for software load balancing, or to fit with a corporate infrastructure, or simply to stick with a known deployment structure.

There are 3 main alternative for connection Apache to Jetty:

1. Using apache mod_proxy and an normal Jetty HTTP connector.
2. Using apache mod_proxy_ajp and the Jetty AJP connector.
3. Using apache mod_jk and the Jetty AJP connector.

Using the HTTP Connectors is greatly preferred, as Jetty performs significantly better with HTTP and the AJP protocol is poorly documented and there are many version irregularities. If AJP is to be used, the then mod_proxy_ajp module is preferred over mod_jk. Previously, the load balancing capabilities of mod_jk meant that it had to be used (tolerated), but with apache 2.2, mod_proxy_balancer is available and load balance over HTTP and AJP connectors.

Using HTTP

THIS IS THE RECOMMENDED MECHANISM TO CONNECT APACHE AND JETTY

To configure apache to use mod_proxy, mod_proxy_http and/or mod_proxy_balancer with HTTP see
Configuring mod_proxy.

Using AJP

AJP is NOT recommended. Use HTTP and mod_proxy instead (see above)

AJP is not recommended for a number of reasons:

• historically mod_jk has had intermittent maintenance and bad versioning practises. This make it difficult to select a known good version that is fully compatible with the AJP connector you are running.
• The mod_proxy plugin is more actively maintained and the mod_proxy_balancer supports a richer set of options for load balancing.
• Jetty is optimized to deal with the text based HTTP protocol and the servlet API also exposes the text nature of HTTP to the application. There are no measurable benefits of using apache to convert text HTTP to the binary AJP protocol, only for jetty to have to convert back. Some tests have shown 15% more throughput with mod_proxy than with mod_ajp
• With cometd style applications, neither mod_jk nor mod_proxy scale well. However, mod_proxy does make greater use of connections, so it is a better choice for moderate comet load. For full comet scaling, either jetty should be directly exposed to the internet or an async load balancer like nginx should be used.
• Note however that AJP is still full supported by the jetty team and we will strive to fix any issues found.

The Jetty AJP connector.

To use AJP with either mod_jk or mod_proxy_ajp, Jetty needs to be configured with an AJP13 connector. This can configured by adding etc/jetty-ajp.xml to the command line. Alternately and existing jetty.xml file may be modified with:

<Call name="addConnector">
  <Arg>
    <New class="org.mortbay.jetty.ajp.Ajp13SocketConnector">
      <Set name="port">8009</Set>
    </New>
  </Arg>
</Call>

The full options for the Ajp13SocketConnector are available in the javadoc.

mod_proxy_ajp

With apache 2.2 mod_proxy_ajp is an extension of the mod_proxy module and may also be used in conjunction with the mod_proxy_balancer module. Prior to 2.2, mod_proxy did not support AJP.

Compatibility

Configuration

The configuration of mod_proxy_ajp is identical to the Configuration of mod_proxy, except that ajp:// may be used as a protocol instead of http:// when specifying destinations (workers) in ProxyPass and BalancerMember elements.

Apache 2.2 normally bundles mod_proxy, mod_proxy_ajp and mod_proxy_balancer, so they often do not need to be installed separately. If they are separately bundled by your operation system (eg as RPMs or debians) ensure that they are installed.

The apache configuration structure can vary greatly with operating system distros and there may be some template configurations for mod_proxy. If not, add the entry below in your httpd.conf apache configuration file located in <apache-root>/conf/ directory

LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_ajp_module modules/mod_proxy_ajp.so
LoadModule proxy_balancer_module modules/mod_proxy_balancer.so

# always keep the host header
ProxyPreserveHost On

# map to cluster
ProxyPass /test balancer://my_cluster/test stickysession=JSESSIONID nofailover=On
ProxyPass /demo balancer://my_cluster/demo stickysession=JSESSIONID nofailover=On

# define the balancer, with http and/ or ajp connections
<Proxy balancer://my_cluster>
    BalancerMember ajp://yourjettyhost1:8009
    BalancerMember ajp://yourjettyhost2:8009
</Proxy>

Where:

• LoadModule - tells your apache server to load a module library and where it is located.
• ProxyPreserveHost On - keeps the original Host Header. THIS IS HIGHLY RECOMMENDED FOR ALL PROXY CONFIGURATIONS
• ProxyPass - Maps a path to a proxied destination. The destination may be a http:// or ajp:// URL to directly map to a single server, or it may be a balancer:// URL to map to a cluster.
• Proxy balancer:// - defines the nodes (workers) in the cluster. Each member may be a {http://}} or ajp:// URL or another balancer:// URL for cascaded load balancing configuration.

mod_jk

It is NOT recommended to use mod_jk

Compatibility

Configuring Apache HTTPD server with mod_jk

1. put mod_jk.so into your <apache-root>/modules/ directory
2. you can download mod_jk.so here http://www.opensourcecommunity.ph/apache/tomcat/tomcat-connectors/jk/binaries/
3. add the entry below in your httpd.conf apache configuration file located in <apache-root>/conf/ directory.
   

   <IfModule !mod_jk.c> LoadModule jk_module modules/mod_jk.so </IfModule> <IfModule mod_jk.c> JkWorkersFile "conf/worker.properties" JkLogFile "logs/mod_jk.log" JkLogLevel info JkLogStampFormat "[%a %b %d %H:%M:%S %Y] " JkOptions +ForwardKeySize +ForwardURICompat </IfModule>

   Where:
4. LoadModule jk_module modules/mod_jk.so tells your apache server to load the mod_jk libray and where it is located.
5. JkWorkersFile conf/worker.properties tells mod_jk where your worker.properties is located.
6. JkLogFile logs/mod_jk.log tells mod_jk where to write mod_jk related Logs.
7. After adding the mod_jk configuration you may add a VirtualHost Entry in the same file (httpd.conf) as long as its located below your mod_jk configuration entry:
   

   <VirtualHost host:*> ServerName yourserver ServerAdmin user@yourserver ## you may add further entries concerning log-files, log-level, URL-rewriting, ... ## pass requests through to jetty worker JkMount /* jetty </VirtualHost>

8. Add a worker file worker.properties in your <apache-root>/conf/
9. add the entries below, and make sure to specify your ip-address or hostname in worker.jetty.host property entry to where your jetty application is runnning
   

   worker.list=jetty worker.jetty.port=8009 worker.jetty.host=<server name or ip where your jetty will be running> worker.jetty.type=ajp13 worker.jetty.lbfactor=1