Configuring mod_proxy

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:

# Using apache [mod_proxy|http://httpd.apache.org/docs/2.2/mod/mod_proxy.html] and an normal Jetty HTTP connector.

# Using apache [mod_proxy_ajp|http://httpd.apache.org/docs/2.2/mod/mod_proxy_ajp.html] and the Jetty AJP connector.

# Using apache [mod_jk|http://tomcat.apache.org/tomcat-3.3-doc/mod_jk-howto.html] 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|http://httpd.apache.org/docs/2.2/mod/mod_proxy_balancer.html] is available and load balance over HTTP and AJP connectors.

h2. mod_proxy

Apache has a mod_proxy module available for almost all versions of apache.  However, prior to apache 2.2, only reverse proxy features were available and mod_proxy_balancer was not available for load balancing.

Documentation for mod_proxy is available for:

* [apache 1.3

|http://httpd.apache.org/docs/1.3/mod/mod_proxy.html]
* [apache 2.0|http://httpd.apache.org/docs/2.0/mod/mod_proxy.html]
* [apache 2.1|http://httpd.apache.org/docs/2.1/mod/mod_proxy.html]
* [apache 2.2|http://httpd.apache.org/docs/2.2/mod/mod_proxy.html]

h3. Configuration as a [Reverse Proxy|http://en.wikipedia.org/wiki/Reverse_proxy]

The configuration file layout for apache varies greatly with version and distribution, but to configure mod_proxy as a reverse proxy, the follow configuration is key:
# Jetty needs to be configured with a normal HTTP connector, probably on port 8080 or similar.
# The proxy module (and other proxy extension used) must be loaded:
\\
{code}
LoadModule proxy_module modules/mod_proxy.so

{code}\\
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.

# Forward proxy needs to be turned off:

\\
{code}
ProxyRequests Off

<Proxy *>
Order deny,allow
Allow from all
</Proxy>

{code}
# Reverse proxy paths must be configured with URL of the jetty server:
\\
{code}
ProxyPass /test http://localhost:8080/test

{code}
# Frequently apache documentation will instruct that {{ProxyPassReverse}} configuration be used so that apache can rewrite any URLs in headers etc.  However, if you use the {{ProxyPreserveHost}} configuration, Jetty can generate the correct URLs and they do not need to be rewritten:
\\
{code}
ProxyPreserveHost On
{code}
Alternatively, since Jetty 6.1.10, instead of preserving the host and to retrieve the client remote address in the webapp ({{ServletRequest#getRemoteAddr()}}) you can use the [forwarded|Configuring Connectors#forwarded] property on {{AbstractConnector

}} which interprets the [mod_proxy_http "x-forwarded-" headers

|http://httpd.apache.org/docs/2.2/mod/mod_proxy.html#x-headers] instead:
{code}
<Configure id="Server" class="org.mortbay.jetty.Server">
  ...
  <Call name="addConnector">
    <Arg>
      <New class="org.mortbay.jetty.nio.SelectChannelConnector">
        <Set name="port">8080</Set>
        <Set name="forwarded">true</Set>
      </New>
    </Arg>
  </Call>
  ...
</Configure>

{code}
Or, to force the result of {{ServletRequest#getServerName()}} and {{ServletRequest#getServerPort()}} (if headers are not available):

{code

}
<Configure id="Server" class="org.mortbay.jetty.Server">
  ...
  <Call name="addConnector">
    <Arg>
      <New class="org.mortbay.jetty.nio.SelectChannelConnector">
        <Set name="port">8080</Set>
        <Set name="forwarded">true</Set>
        <Set name="hostHeader">example.com:81</Set>
      </New>
    </Arg>
  </Call>
  ...
</Configure>

{code}\\
*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.

If the worker name is not set for the Jetty servers, then session affinity (sticky sessions) will not work. The JSESSIONID cookie must have the format {{<sessionID>.<worker name>}}, in which {{worker name}} has the same value as the {{route}} specified in the BalancerMember above (in this case "jetty1" and "jetty2"). See [this article|http://www.markround.com/archives/33-Apache-mod_proxy-balancing-with-PHP-sticky-sessions.html] for details. The following can be added to the {{jetty-web.xml}} in the {{WEB-INF}} directory to set the worker name.

{code

}
<Configure class="org.mortbay.jetty.webapp.WebAppContext">
  <Get name="sessionHandler">
    <Get name="sessionManager">
      <Call name="setIdManager">
        <Arg>
          <New class="org.mortbay.jetty.servlet.HashSessionIdManager">
            <Set name="WorkerName">jetty1</Set>
          </New>
        </Arg>
      </Call>
    </Get>
  </Get>
</Configure>