Before integrating Resin with Apache, it is valuable to configure Resin as a standalone server, especially with more complicated setups such as those involving virtual hosts. Doing so isolates the steps and makes troubleshooting easier.

Many users find that the performance, flexibility, and features of Resin make Resin a desirable replacement for Apache.

How Resin integrates with Apache

When used with Apache, Resin serves JSPs and Servlets and Apache serves static content like html and images. Apache is a frontend server, it handles the request from the browser. Resin's mod_caucho plugin integrates with Apache, it dispatches requests for JSPs and Servlets to one or more backend Resin servers.

mod_caucho queries the backend server to distinguish the URLs going to Resin from the URLs handled by Apache. The backend server uses the <servlet-mapping> directives to decide which URLs to send. Also, any *.war file automatically gets all its URLs. Other URLs stay with Apache.

There's a more complete discussion of the URL dispatching in the How the Plugins Dispatch to Resin page.

Unix Installation

Resin needs Apache 1.3.x or greater and DSO support.

To configure Resin with Apache, you must follow the following steps:

Compile Apache
Compile mod_caucho.so
Configure Apache
Set up environment
Configure resin.xml
Restart Apache and start the backend Resin server

Compiling Apache

You need a version of Apache with DSO support enabled. Apache has full documentation at their website. To check if your apache has DSO support, you can check for mod_so.c in your your httpd

checking apache httpd for mod_so.c

unix> /usr/local/apache/bin/httpd -l
Compiled-in modules:
  ...
  mod_so.c
  ...

Many distributions, e.g. Red Hat Linux, will have Apache preinstalled. However, because the standard distribution has files all over the place, some people prefer to recompile Apache from scratch.

Once you untar Apache, build it like:

unix> ./configure --prefix=/usr/local/apache --enable-module=so
unix> make
unix> make install

Solaris versions of Apache may need additional flags, otherwise you'll get some linking errors when trying to load Resin. You may need to refer to the Apache documentation if you get linking errors. Here's an example configuration on Solaris:

unix> ./configure --prefix=/usr/local/apache \
                  --enable-rule=SHARED_CORE \
                  --enable-rule=SHARED_CHAIN \
                  --enable-module=so \
                  --enable-module=most \
                  --enable-shared=max

Compiling mod_caucho.so

To compile and install mod_caucho on Unix, you'll need to run Resin's configure and then make. This step will create mod_caucho.so and put it in the Apache module directory. Usually, mod_caucho.so will end up in /usr/local/apache/libexec/mod_caucho.so.

If you know where your apxs executable is, you can use --with-apxs. apxs is a little Perl script that the Apache configuration makes. It lets modules like Resin know how all the Apache directories are configured. It is generally in /usr/local/apache/bin/apxs or /usr/sbin/apxs. It's usually easiest to use --with-apxs so you don't need to worry where all the Apache directories are.

unix> ./configure --with-apxs=/usr/local/apache/bin/apxs
unix> make

Even if you don't know where apxs is, the configure script can often find it:

unix> ./configure --with-apxs
unix> make

As an alternative to --with-apxs, if you've compiled Apache yourself, or if you have a simple configuration, you can generally just point to the Apache directory:

unix> ./configure --with-apache=/usr/local/apache
unix> make
unix> make install

The previous --with-apxs or --with-apache should cover most configurations. For some unusual configurations, you can have finer control over each directory with the following arguments to ./configure. In general, you should use --with-apache or --with-apxs, but the other variables are there if you know what you're doing.

--with-apache=dir	The Apache root directory.
--with-apxs=apxs	Pointer to the Apache extension script
--with-apache-include=dir	The Apache include directory
--with-apache-libexec=dir	The Apache module directory
--with-apache-conf=httpd.conf	The Apache config file

Configure the Environment

If you don't already have Java installed, you'll need to download a JDK and set some environment variables.

Here's a typical environment that you might put in ~/.profile or /etc/profile

# Java Location
JAVA_HOME=/usr/java
export JAVA_HOME

# Resin location (optional).  Usually Resin can figure this out.
RESIN_HOME=/usr/local/resin
export RESIN_HOME

# If you're using additional class libraries, you'll need to put them
# in the classpath.
CLASSPATH=

Windows Installation

The setup.exe program installs the mod_caucho.dll plugin for any Apache it finds, and modifies the Apache httpd.conf file.

The httpd.conf file is also easily modified manually:

httpd.conf

LoadModule caucho_module \
    <installdir>/resin-pro-4.0.17/win32/apache-2.2/mod_caucho.dll

ResinConfigServer localhost 6800
<Location /caucho-status>
  SetHandler caucho-status
</Location>

Configuring resin.xml

The communication between mod_caucho and the backend Resin server takes place using a server port.

The resin.xml for the backend server contains a server to enable the port. The default resin.xml has an server listener on port 6800.

resin.xml

<resin xmlns="http://caucho.com/ns/resin"
       xmlns:resin="http://caucho.com/ns/resin/core">

  ...


  <cluster id="app-tier">

    ...

    <server id="" address="127.0.0.1" port="6800"/>

    ...

The resin.xml and the layout of your webapps should match the layout that Apache expects. The mapping of urls to filesystem locations should be consistent between Apache and the backend Resin server.

The default resin.xml looks in resin-4.0.x/webapps/ROOT for JSP files and resin-4.0.x/webapps/ROOT/WEB-INF/classes for servlets and java source files. To tell Resin to use Apache's document area, you configure an explicit web-app with the appropriate document-directory:

resin.xml

<resin xmlns="http://caucho.com/ns/resin"
       xmlns:resin="http://caucho.com/ns/resin/core">

  ...

  <server>

    ...

    <host id="">
 
      <web-app id='/' document-directory="/usr/local/apache/htdocs"/>

    </host>

    ...

  </server>
</resin>

Starting the app-tier Resin server

Now you need to start the app-tier Resin server. Starting Resin is the same with Apache or standalone. See the Resin Web Server page for a detailed description.

unix> java -jar $RESIN_HOME/lib/resin.jar start 

unix> bin/resin.sh start

win> resin.exe

May 6, 2011 3:06:05 PM com.caucho.boot.WatchdogChildTask run
INFO: WatchdogChild[] starting
May 6, 2011 3:06:05 PM com.caucho.boot.WatchdogChildProcess run
WARNING: Watchdog starting Resin[]
Resin Professional 4.0.17 (built Fri, 15 Apr 2011 06:35:56 PDT)
Copyright(c) 1998-2010 Caucho Technology.  All rights reserved.

  current.license -- 1 Resin server Caucho

Starting Resin Professional on Fri, 06 May 2011 15:06:06 -0400 (EDT)

[11-05-06 15:06:07.824] {main} Proxy Cache disk-size=1024M memory-size=64M
[11-05-06 15:06:08.179] {main} 
[11-05-06 15:06:08.179] {main} Mac OS X 10.6.7 x86_64
[11-05-06 15:06:08.179] {main} Java(TM) SE Runtime Environment 1.6.0_24-b07-334-10M3326, MacRoman, en
[11-05-06 15:06:08.179] {main} Java HotSpot(TM) 64-Bit Server VM 19.1-b02-334, 64, mixed mode, Apple Inc.
[11-05-06 15:06:08.179] {main} 
[11-05-06 15:06:08.179] {main} user.name  = caucho
[11-05-06 15:06:08.472] {main} 
[11-05-06 15:06:08.479] {main} server listening to localhost:6800
[11-05-06 15:06:08.555] {main} 
[11-05-06 15:06:08.873] {main} 
[11-05-06 15:06:08.874] {main} resin.home = /Users/caucho/resin-pro-4.0.17/
[11-05-06 15:06:08.878] {main} resin.root = /Users/caucho/resin-pro-4.0.17/
[11-05-06 15:06:08.879] {main} resin.conf = /Users/caucho/resin-pro-4.0.17/conf/resin.xml
[11-05-06 15:06:08.889] {main} 
[11-05-06 15:06:08.889] {main} server    = 127.0.0.1:6800 (app-tier:default)
[11-05-06 15:06:08.899] {main} stage      = production
[11-05-06 15:06:09.526] {main} WebApp[production/webapp/default/resin-admin] active
[11-05-06 15:06:10.245] {main} WebApp[production/webapp/default/resin-doc] active
[11-05-06 15:06:10.445] {main} WebApp[production/webapp/default/ROOT] active
[11-05-06 15:06:10.446] {main} Host[production/host/default] active
[11-05-06 15:06:10.447] {main} ProServer[id=default,cluster=app-tier] active
[11-05-06 15:06:10.448] {main}   JNI: file, nio keepalive (max=9984), socket
[11-05-06 15:06:10.448] {main} 
[11-05-06 15:06:10.449] {main} 
[11-05-06 15:06:10.450] {main} http listening to *:8080
[11-05-06 15:06:11.023] {main} https listening to *:8443
[11-05-06 15:06:11.092] {main} 
[11-05-06 15:06:11.160] {main} ProResin[id=default] started in 4222ms

Resin will print every port it's listening to. In the above example, Resin has an http listener on port 8080 and an server listener on port 6800 (using its custom 'hmux' protocol). mod_caucho establishes connections to Resin using port 6800, and a web browser can connect using port 8080. Usually the 8080 port will be unused, because web browsers will make requests to Apache, these requests get dispatched to Resin as needed by mod_caucho. A Resin configured http listener on port 8080 is a useful debugging tool, it allows you to bypass Apache and make a request straight to Resin.

The following snippet shows the <http> and <server> configuration for the above example.

<resin xmlns="http://caucho.com/ns/resin">
  <cluster id="app-tier">
    <server-default>
      <http address="*" port="8080"/>
    </server-default>

    <server id="" address="192.168.2.10" port="6800"/>

    ...
  </cluster>
</resin>

Testing the servlet engine

Create a test file '/usr/local/apache/htdocs/test.jsp'

2 + 2 = <%= 2 + 2 %>

Browse http://localhost/test.jsp again. You should now get

2 + 2 = 4

Configuring Apache httpd.conf

The installation process above automatically changes the httpd.conf file. You can also configure the httpd.conf file manually, or modify the default configuration created by the installation process.

Unix - httpd.conf

LoadModule caucho_module libexec/mod_caucho.so

ResinConfigServer localhost 6800
<Location /caucho-status>
  SetHandler caucho-status
</Location>

Windows - httpd.conf

LoadModule caucho_module \
    <installdir>/resin-pro-4.0.17/win32/apache-2.2/mod_caucho.dll

ResinConfigServer localhost 6800
<Location /caucho-status>
  SetHandler caucho-status
</Location>

The ResinConfigServer is used to tell mod_caucho how to contact the backend Resin server. The backend Resin server tell's mod_caucho which urls should be dispatched.

APACHE COMMAND	MEANING
ResinConfigServer hostport	Specifies the Resin JVM at host:port as a configuration server.

caucho-status

caucho-status is optional and probably should be avoided in a production site. It lets you ask the Caucho Apache module about it's configuration, and the status of the backend server(s), valuable for debugging.

After any change to httpd.conf, restart Apache. Now browse http://localhost/caucho-status.

Manual configuration of dispatching

You can also dispatch to Resin directly from the httpd.conf. Instead of relying on the ResinConfigServer directive to determine which url's to dispatch to the backend server, Apache handler's are used to specify the url's to dispatch.

CauchoHost 127.0.0.1 6800

<Location /foo/*>
  SetHandler caucho-request
</Location>

APACHE COMMAND	MEANING
CauchoHost hostport	Alternative to ResinConfigServer, adds the Resin JVM with an server port at host:port as a backend server.
CauchoBackup hostport	Alternative to ResinConfigServer, adds the Resin JVM with a server port at host:port as a backup backend server.

APACHE HANDLER	MEANING
caucho-status	Handler to display /caucho-status
caucho-request	Dispatch a request to Resin

Requests dispatched directly from the Apache httpd.conf will not appear in /caucho-status.

Virtual Hosts

The virtual host topic describes virtual hosts in detail. If you're using a single JVM, you only need to configure the resin.xml.

httpd.conf

LoadModule caucho_module libexec/mod_caucho.so

ResinConfigServer 192.168.0.1 6800
<Location /caucho-status>
  SetHandler caucho-status
</Location>

resin.xml

<resin xmlns="http://caucho.com/ns/resin">
<cluster id="app-tier">

  <server id="" address="192.168.0.1" port="6800"/>

  <host id='www.gryffindor.com'>
    <host-alias>gryffindor.com</host-alias>
     ...
  </host>

  <host id='www.slytherin.com'>
    <host-alias>slytherin.com</host-alias>
     ...
  </host>
</cluster>
</resin>

Virtual Host per JVM

If you want a different JVM for each virtual host, your httpd.conf can specify a different server port for each host.

httpd.conf

<VirtualHost gryffindor.com>
ServerName gryffindor.com
ServerAlias www.gryffindor.com
ResinConfigServer 192.168.0.1 6800
</VirtualHost>

<VirtualHost slytherin.com>
ServerName slytherin.com
ServerAlias www.slytherin.com
ResinConfigServer 192.168.0.1 6801
</VirtualHost>

gryffindor.conf

<resin xmlns="http://caucho.com/ns/resin">
<cluster id="">

  <server id="" address="192.168.0.1" port="6800"/>

  <host id="">
     ...
  </host>
</cluster>
</resin>

slytherin.conf

<resin xmlns="http://caucho.com/ns/resin">
<cluster>

  <server id="" address="192.168.0.1" port="6801"/>

  <host id="">
     ...
  </host>
</cluster>
</resin>

$ bin/resin.sh -pid gryffindor.pid -conf conf/gryffindor.conf start
$ bin/resin.sh -pid slytherin.pid -conf conf/slytherin.conf start

...

$ bin/resin.sh -pid gryffindor.pid stop

Load Balancing

The Reliability and Load Balancing section provides an introduction to the concepts of load balancing.

mod_caucho recognizes cluster configurations for load balancing. Requests are distributed to all machines in the cluster, all requests in a session will go to the same host, and if one host goes down, Resin will send the request to the next available machine. Optional backup machines only receive requests if all of the primaries are down.

resin.xml

<resin xmlns="http://caucho.com/ns/resin">
  <cluster id="app-tier">
    <server id="a" address="192.168.0.11" port="6800" index="1"/>
    <server id="b" address="192.168.0.11" port="6801" index="2" 
             backup="true"/>
    <server id="c" address="192.168.0.12" port="6800" index="3"/>
    <server id="d" address="192.168.0.12" port="6801" index="4" 
             backup="true"/>
    ...
  </cluster>
</resin>

mod_caucho only needs to know about one of the backend servers. It will query that backend server, and learn about all of the other members of the cluster.

ResinConfigServer 192.168.0.11 6800

mod_caucho keeps a local cache of the configuration information, so if the backend server becomes unavailable then the cached configuration will be used until the backend server becomes available again.

The httpd.conf file can also specify more than one backend server, when mod_caucho checks for configuration updates, it will check each in turn, and only if none of them are available will it use the local cached copy.

ResinConfigServer 192.168.0.11 6800
ResinConfigServer 192.168.0.12 6801

Manual configuration of load balanced dispatching

Manual dispatching in httpd.conf can also specify the backend hosts and the backend backup hosts, as an alternative to using ResinConfigServer.

CauchoHost 192.168.0.11 6800
CauchoBackup 192.168.0.11 6801
CauchoHost 192.168.0.12 6800
CauchoBackup 192.168.0.12 6801

<Location /foo/*>
  SetHandler caucho-request
</Location>

Manual configuration of location based dispatching

<Location /applicationA/*>
  ResinConfigServer 192.168.0.11 6800
</Location>

<Location /applicationB/*>
  ResinConfigServer 192.168.0.12 6800
</Location>

Troubleshooting

First, check your configuration with Resin standalone.sh. In other words, add a <http port='8080'/> and check port 8080.
Check http://localhost/caucho-status. That will tell if mod_caucho has properly connected to the backend Resin server.
Each server should be green and the mappings should match your resin.xml.
If caucho-status fails entirely, the problem is in the mod_caucho installation and the Apache httpd.conf.
If caucho-status shows the wrong mappings, there's something wrong with the resin.xml or the pointer to the backend server in httpd.conf.
If caucho-status shows a red servlet runner, then Resin hasn't properly started.
If you get a "cannot connect to servlet engine", caucho-status will show red, and Resin hasn't started properly.
If Resin doesn't start properly, you should look at the logs in resin-4.0.x/log. You should start resin.sh -verbose or resin.exe -verbose to get more information.
If Resin never shows a "hmux listening to *:6800" line, it's not listening for connections from mod_caucho. You'll need to add a <server> line.
If you get Resin's "file not found", the Apache configuration is good but the resin.xml probably points to the wrong directories.