Apache

Revision as of 16:03, 8 March 2006

When used with Apache, Resin installs a Apache module named mod_caucho and dispatches JSPs and Servlets to backend Resin servers while Apache serves static content like html and images.

Before you integrate Resin with Apache

Many users find that the performance, flexibility, and features of Resin make Resin a desirable replacement for Apache. Resin, for example, serves static content as fast or faster than Apache. Unless specific features of Apache are required, consider running Resin as the primary web server.

If you have not yet done so, follow the Resin web server instructions and get a working installation with Resin as the only web server. This is especially true with more complicated setups such as those involving virtual hosts. Doing so isolates the steps and makes troubleshooting easier.

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.

File:Apache srun.gif

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. Any *.war file automatically causes Resin to gets all URLs with the corresponding prefix. Other URLs stay with Apache.

Unix

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

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

1. Compile Apache
2. Compile mod_caucho.so
3. Configure Apache
4. Set up environment
5. Configure resin.conf
6. Restart Apache and start the backend Resin server

Compile Apache

You need a version of Apache with DSO support enabled. Apache has full documentation at [[1]] To check if your apache has DSO support, you can check for mod_so.c in your httpd binary:

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

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Many Unix installations 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:

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

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Solaris versions of Apache may need additional flags, otherwise there are 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:

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

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Compile mod_caucho.so

To compile and install mod_caucho on Unix, you'll need to run Resin's configure script. 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.

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

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

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

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

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

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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.

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

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# Java Location
JAVA_HOME=/<installdir>/jdk1.4
export JAVA_HOME

# Resin location (optional).  Usually Resin can figure this out.
RESIN_HOME=/<installdir>/resin-pro-3.0.2
export RESIN_HOME

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

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Windows

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

Configure resin.conf

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

The resin.conf for the backend server contains an srun to enable the port. The default resin.conf has an srun listener on port 6802.

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<resin xmlns="http://caucho.com/ns/resin"
       xmlns:resin="http://caucho.com/ns/resin/core">
 
  ...
 
  <server>
 
    ...
 
    <cluster>
      <srun server-id="" host="127.0.0.1" port="6802"/>
    </cluster>
 
    ...

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The resin.conf 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.conf looks in resin-pro-3.0.x/webapps/ROOT for JSP files and resin-pro-3.0.x/webapps/ROOT/WEB-INF/classes for servlets and java source files. To tell Resin to use Apache's document area, configure an explicit web-app with the appropriate document-directory:

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<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>

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Start the backend Resin server

Now you need to start the backend Resin server. Starting Resin is the same with Apache or standalone. See the Resin web server page for a detailed description.

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 unix> bin/httpd.sh
 
 win> httpd.exe

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Resin-pro-3.0.x (built Fri, 03 Feb 2006 09:47:48 EST)
Copyright(c) 1998-2006 Caucho Technology.  All rights reserved.
    
Starting Resin on Mon, 13 Feb 2006 20:16:19 -0500 (EST)
 
[09:43:40.664] Loaded Socket JNI library.
[09:43:40.664] http listening to *:8080
[09:43:40.664] ServletServer[] starting
[09:43:40.879] hmux listening to *:6802
[09:43:41.073] Host[] starting
[09:43:41.446] Application[2] starting
[09:43:41.496] Application[3] starting

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Resin will print every port it's listening to. In the above example, Resin has an http listener on port 8080 and an srun listener on port 6802 (using its custom `hmux' protocol). mod_caucho establishes connections to Resin using port 6802, 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 srun configuration for the above example.

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<resin xmlns="http://caucho.com/ns/resin">
  <server>
    <http id="" host="*" port="8080"/>

    <cluster>
      <srun id="" host="localhost" port="6802" index="1"/>
    </cluster>

    ...
  </server>
</resin>

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Test the servlet engine

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

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2 + 2 = <%= 2 + 2 %>

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

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2 + 2 = 4

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Configure 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:

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LoadModule caucho_module libexec/mod_caucho.so

ResinConfigServer localhost 6802
<Location /caucho-status>
  SetHandler caucho-status
</Location>

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Windows:

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LoadModule caucho_module <installdir>/resin-pro-3.0.x/libexec/apache-2.0/mod_caucho.dll
 
ResinConfigServer localhost 6802
<Location /caucho-status>
  SetHandler caucho-status
</Location>

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ResinConfigServer

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.

mod_caucho discovers its configuration by contacting the ResinConfigServer specified in the httpd.conf or resin.ini. The ResinConfigServer can be any Resin server. When a user requests a URL, mod_caucho uses the configuration it has determined from the ResinConfigServer to determine whether Resin or Apache should handle the request. That decision is based on the configuration in the ResinConfigServer's resin.conf.

After reading the configuration from the backend Resin instance, mod_caucho keeps a local cahce of the information on disk. If the backend server becomes unavailable, mod_caucho uses the last known configuration until the backend server is again available to provide the configuration information.

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.

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CauchoHost 127.0.0.1 6802

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

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

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

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LoadModule caucho_module libexec/mod_caucho.so
 
ResinConfigServer 192.168.0.1 6802
<Location /caucho-status>
  SetHandler caucho-status
</Location>

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<resin xmlns="http://caucho.com/ns/resin">
<server>
  <cluster>
    <srun id="" host="192.168.0.1" port="6802"/>
  </cluster>
 
  <host id='www.gryffindor.com'>
    <host-alias>gryffindor.com</host-alias>
     ...
  </host>
 
  <host id='www.slytherin.com'>
    <host-alias>slytherin.com</host-alias>
     ...
  </host>
</server>
</resin>

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Special servlet-mappings

There are two special servlet-names which only affect the plugins: plugin_match and plugin_ignore.

plugin_match will direct a request to Resin. The servlet engine itself will ignore the plugin_match directive. You can use plugin_match to direct an entire subtree to Resin, e.g. to workaround the regexp limitation, but allow Resin's other servlet-mapping directives to control which servlets are used.

plugin_ignore keeps the request at on the web server. So you could create a directory /static where all documents, including JSPs are served by the web server.

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 <servlet-mapping url-pattern='/resin/*'
                  servlet-name='plugin_match'/>

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 <servlet-mapping url-pattern='/static/*'
                  servlet-name='plugin_ignore'/>

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Virtual host per JVM

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

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<VirtualHost gryffindor.com>
ServerName gryffindor.com
ServerAlias www.gryffindor.com
ResinConfigServer 192.168.0.1 6802
</VirtualHost>
 
<VirtualHost slytherin.com>
ServerName slytherin.com
ServerAlias www.slytherin.com
ResinConfigServer 192.168.0.1 6803
</VirtualHost>

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<resin xmlns="http://caucho.com/ns/resin">
<server>
  <cluster>
    <srun id="" host="192.168.0.1" port="6802"/>
  </cluster>
 
  <host id=>
     ...
  </host>
</server>
</resin>

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<resin xmlns="http://caucho.com/ns/resin">
<server>
  <cluster>
    <srun id="" host="192.168.0.1" port="6803"/>
  </cluster>
 
  <host id=>
     ...
  </host>
</server>
</resin>

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

...

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

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Load balancing

The 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.

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<resin xmlns="http://caucho.com/ns/resin">
<server>
  <cluster>
    <srun id="a" host="192.168.0.11" port="6802" index="1"/>
    <srun id="b" host="192.168.0.11" port="6803" index="2" backup="true"/>
    <srun id="c" host="192.168.0.12" port="6802" index="3"/>
    <srun id="d" host="192.168.0.12" port="6803" index="4" backup="true"/>
  </cluster>
  ...
</server>
</resin>

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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.

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ResinConfigServer 192.168.0.11 6802

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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.

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ResinConfigServer 192.168.0.11 6802
ResinConfigServer 192.168.0.12 6802

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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.

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CauchoHost 192.168.0.11 6802
CauchoBackup 192.168.0.11 6803
CauchoHost 192.168.0.12 6802
CauchoBackup 192.168.0.12 6803

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

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Manual configuration of location based dispatching

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<Location /applicationA/*>
  ResinConfigServer 192.168.0.11 6802
</Location>

<Location /applicationB/*>
  ResinConfigServer 192.168.0.12 6802
</Location>

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Troubleshooting

1. First, check your configuration with Resin standalone.sh. In other words, add a <http port='8080'/> and check port 8080.
2. Check http://localhost/caucho-status. That will tell if mod_caucho has properly connected to the backend Resin server.
3. Each srun host should be green and the mappings should match your resin.conf.
4. If caucho-status fails entirely, the problem is in the mod_caucho installation and the Apache httpd.conf.
5. If caucho-status shows the wrong mappings, there's something wrong with the resin.conf or the pointer to the backend server in httpd.conf.
6. If caucho-status shows a red servlet runner, then Resin hasn't properly started.
7. If you get a "cannot connect to servlet engine", caucho-status will show red, and Resin hasn't started properly.
8. If Resin doesn't start properly, you should look at the logs in resin-pro-3.0.x/log. You should start httpd.sh -verbose or httpd.exe -verbose to get more information.
9. If Resin never shows a "srun listening to *:6802" line, it's not listening for connections from mod_caucho. You'll need to add a srun directive..
10. If you get Resin's "file not found", the Apache configuration is good but the resin.conf probably points to the wrong directories.

Debug logging

Debug logging output from mod_caucho is created with the --enable-debug option to ./configure. It causes a large amount of information to be dumped to /tmp/log, probably not suitable for a production environment,

./configure --enable-debug --with-apache=...