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 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.
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.
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:
- 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:
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:
- Reverse proxy paths must be configured with URL of the jetty server:
- Frequently apache documentation will instruct that
ProxyPassReverseconfiguration be used so that apache can rewrite any URLs in headers etc. However, if you use the
ProxyPreserveHostconfiguration, Jetty can generate the correct URLs and they do not need to be rewritten:
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
AbstractConnectorwhich interprets the mod_proxy_http "x-forwarded-" headers instead: Or, to force the result of
ServletRequest#getServerPort()(if headers are not available):
- It is also very useful to turn on proxy status monitoring (see management below):
The situation here is:
public void customize(org.mortbay.io.EndPoint endpoint, Request request) throws IOException
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
Proxy balancer:// - defines the nodes (workers) in the cluster. Each member may be a
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.
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:
These UIs should be protected from external access.