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Configuring Apache mod_proxy with Jetty

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.

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:

Configuration as a 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:

  1. Jetty needs to be configured with a normal HTTP connector, probably on port 8080 or similar.
  2. The proxy module (and other proxy extension used) must be loaded:
    Code Block
    LoadModule proxy_module modules/mod_proxy.so
    

    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.
  3. Forward proxy needs to be turned off:
    Code Block
    ProxyRequests Off
    
    <Proxy *>
    Order deny,allow
    Allow from all
    </Proxy>
    
  4. Reverse proxy paths must be configured with URL of the jetty server:
    Code Block
    ProxyPass /test http://localhost:8080/test
    
  5. 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 Block
    ProxyPreserveHost On
    
    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 property on AbstractConnector which interprets the mod_proxy_http "x-forwarded-" headers instead:
    Code Block
    <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>
    
    Or, to force the result of ServletRequest#getServerName() and ServletRequest#getServerPort() (if headers are not available):
    Code Block
    <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>
    

  6. It is also very useful to turn on proxy status monitoring (see management below):
    Code Block
    ProxyStatus On
    

Proxying SSL on Apache to HTTP on Jetty

The situation here is:

Code Block
  https                 http
--------->   Apache   -------> Jetty

If you want to offload the SSL onto Apache, and then use plain http requests to your Jetty backend, you need to configure Jetty to use https:// in all redirected requests.

You can do that by extending the Connector class of your choice, eg the SelectChannelConnector, and implement the customize(EndPoint, Request) method to force the scheme of the Request to be https like so ( don't forget to call super.customize(endpoint,request)! ):

Code Block
public void customize(org.mortbay.io.EndPoint endpoint, Request request) throws IOException
{
    request.setScheme("https");
    super.customize(endpoint, request);
}

If you need access on Jetty to some of the SSL information accessible on Apache, then you need to some configuration tricks on Apache to insert the SSL info as headers on outgoing requests. Follow the Apache configuration suggestions on this tutorial which shows you how to use mod_headers to insert the appropriate request headers. Of course you will also need to code your application to look for the corresponding custom request headers bearing the ssl information.

mod_proxy_balancer

With apache 2.2 mod_proxy is able to use the extension mod_proxy_balancer

Configuration

The configuration of mod_proxy_balancer is similar to pure mod_proxy, except that balancer:// URLs may be used as a protocol instead of http:// when specifying destinations (workers) in ProxyPass elements.

Code Block
# map to cluster with session affinity (sticky sessions)
ProxyPass /balancer !
ProxyPass / balancer://my_cluster/ stickysession=jsessionid nofailover=On

<Proxy balancer://my_cluster>
    BalancerMember http://yourjetty1:8080 route=jetty1
    BalancerMember http://yourjetty2:8080 route=jetty2
</Proxy>


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 for details. The following can be added to the jetty-web.xml in the WEB-INF directory to set the worker name.

Code Block
<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>

Management

Apache provide mod_status and Balancer Manager Support so that the status of the proxy and balancer can be viewed on a web page. The following configuration enables these UIs at /balancer and /status URLs:

Code Block
<Location /balancer>
SetHandler balancer-manager

Order Deny,Allow
Deny from all
Allow from all
</Location>


ProxyStatus On
<Location /status>
SetHandler server-status

Order Deny,Allow
Deny from all
Allow from all
</Location>

These UIs should be protected from external access.

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