Difference between revisions of "Jetty/Howto/Configure mod proxy"

Revision as of 17:14, 26 April 2011

Introduction

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.

Configuring Apache mod_proxy with Jetty

Ways to connect Apache to Jetty include:

• Using Apache mod_proxy and an normal Jetty HTTP connector.
• Using Apache mod_proxy_ajp and the Jetty AJP connector.
• Using Apache mod_jk and the Jetty AJP connector.

We recommend using the HTTP connectors for the following reasons:

• Jetty performs significantly better with HTTP.
• The AJP protocol is poorly documented and has many version irregularities.

If you must use AJP, the mod_proxy_ajp module is better than mod_jk. Previously, the load balancing capabilities of mod_jk meant that you had to use (tolerate) it, but with Apache 2.2, mod_proxy_balancer is available and works over HTTP and AJP connectors.

mod_proxy

A mod_proxy module is 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
• apache 2.0
• apache 2.1
• apache 2.2

Configuring mod_proxy 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 following is key:

1. Configure Jetty with a normal HTTP connector, on port 8080 or similar.
2. Load the proxy module (and any other proxy extension used):

 
 LoadModule proxy_module modules/mod_proxy.so

Apache 2.2 normally bundles mod_proxy, mod_proxy_ajp, and mod_proxy_balancer, so often you do not need to install them separately. If they are bundled separately in your operating system, for example, as RPMs or Debians, be sure to install them.

1. Turn off forward proxy.

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

1. Configure reverse proxy paths with the URL of the Jetty server:

 
 ProxyPass /test http://localhost:8080/test

1. Frequently Apache documentation instructs that you use ProxyPassReverse configuration so that Apache can rewrite any URLs in headers. However, if you use the ProxyPreserveHost configuration, Jetty can generate the correct URLs, and rewriting is not necessary:

 
 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 ConfiguringConnectors-forwarded forwarded property on AbstractConnector, which interprets the mod_proxy_http "x-forwarded-" headers instead:

 
 <Configure id="Server" class="org.eclipse.jetty.Server">
   ...
   <Call name="addConnector">
     <Arg>
       <New class="org.eclipse.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):

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

1. It is also very useful to turn on proxy status monitoring (see management below):

 ProxyStatus On

Proxying SSL on Apache to HTTP on Jetty

The situation here is:

 <nowiki>
   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)! ):

 
 public void customize(org.eclipse.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 do 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.

Configuring mod_proxy_balancer

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.

 # map to cluster with session affinity (sticky sessions)
 ProxyPass /balancer !
 ProxyPass / balancer:</nowiki>//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 can 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) does 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. You can add the following to the jetty-web.xml in the WEB-INF directory to set the worker name.

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

Managing mod_proxy_balancer

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

 
 <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.