Thursday Jan 29, 2009

TOTD #67: How to front-end a GlassFish Cluster with Apache + mod_jk on Mac OSX Leopard ?

GlassFish provides support for High Availability by creating a cluster of server instances and session state replication. This enhances the scalability and availability of your application and is a critical piece of decision making critieria when selecting an Application Server. Clustering in GlassFish Version 2 provides comprehensive introduction to clustering, high availability and load balancing in GlassFish.

GlassFish provides out-of-the-box support for load-balancing HTTP(S), JMS, and RMI/IIOP traffic and front-ended by Sun Java System Web Server, Apache Web Server, and Microsoft IIS (more details here) using the Load Balancer plug-in. This plug-in however is not available for Mac OS X and a popular technique used on that platform for front-ending is to use Apache httpd + mod_jk. This is exactly what this TOTD (Tip Of The Day) is going to describe.

This TOTD is going to explain how to front-end a 3-instance GlassFish cluster with Apache httpd and mod_jk on Mac OS X.

This blog is using information from the following blogs:
And thanks to Vivek and Shreedhar for helping me understand the guts of GlassFish High Availability.

Without further ado, lets get started. The steps are slightly involving so strap your seatbelts!
  1. First, lets create a 3-instance cluster following the screencast at GlassFish Clustering in under 10 minutes. Use the cluster name as "cluster1" and instance names as "instance1", "instance2", "instance3". The admin console will look like:

    Deploy "clusterjsp" and make sure it works using port hopping as explained in the screencast. Click on each instance to identify their associated HTTP port.
  2. Define "jvmRoute" and "enableJK" properties on the newly created cluster as:

    ~/samples/v2/clustering/glassfish/bin >./asadmin create-jvm-options --target cluster1 "-DjvmRoute=\\${AJP_INSTANCE_NAME}"
    Command create-jvm-options executed successfully.
    ~/samples/v2/clustering/glassfish/bin >./asadmin create-jvm-options --target cluster1 "-Dcom.sun.enterprise.web.connector.enableJK=\\${AJP_PORT}"
    Command create-jvm-options executed successfully.

    These properties are required to enable "stickiness" for "mod_jk". More details about how these properties are used internally is explained here.
  3. Configure the above system properties for each instance in the cluster as shown:

    ~/samples/v2/clustering/glassfish/bin >./asadmin create-system-properties --target instance1 AJP_INSTANCE_NAME=instance1
    Command create-system-properties executed successfully.
    ~/samples/v2/clustering/glassfish/bin >./asadmin create-system-properties --target instance1 AJP_PORT=9090
    Command create-system-properties executed successfully.
    ~/samples/v2/clustering/glassfish/bin >./asadmin create-system-properties --target instance2 AJP_INSTANCE_NAME=instance2
    Command create-system-properties executed successfully.
    ~/samples/v2/clustering/glassfish/bin >./asadmin create-system-properties --target instance2 AJP_PORT=9091
    Command create-system-properties executed successfully.
    ~/samples/v2/clustering/glassfish/bin >./asadmin create-system-properties --target instance3 AJP_INSTANCE_NAME=instance3
    Command create-system-properties executed successfully.
    ~/samples/v2/clustering/glassfish/bin >./asadmin create-system-properties --target instance3 AJP_PORT=9092
    Command create-system-properties executed successfully.

    Note the value of "AJP_PORT" property for each instance, this will be used for configuring "mod_jk" later. You may have to restart the cluster in order for these properties to be synchronized for each instance. This can be easily done using the admin console as explained in the screencast above.
  4. Install httpd: Mac OS X Leopard 10.5.6 comes bundled with Apache httpd 2.2, so that's cool! Otherwise it can be downloaded from However in the pre-installed version there are some intricacies with directory names that are explained below.
  5. Lets install and configure "mod_jk" in "httpd".
    1. The mod_jk binaries for Mac OSX are supposedly available at But installing the available module in httpd gives the following error:

      httpd: Syntax error on line 116 of /private/etc/apache2/httpd.conf: Cannot load /usr/libexec/apache2/ into server: dlopen(/usr/libexec/apache2/, 10): no suitable image found.  Did find:\\n\\t/usr/libexec/apache2/ mach-o, but wrong architecture
    2. The alternative is to build "mod_jk". Fortunately it turned out to be a straight forward process because of this blog.
      1. Download latest Connectors source code (version 1.2.27). The file "BUILD.txt" (included in the source bundle) provide clear instructions to build and described below as well.
      2. Configure the build environment as shown:

        ~/workspaces/tomcat-connectors-1.2.27-src/native >./configure --with-apxs=/usr/sbin/apxs

        It shows the output as:

        . . .
        checking for target platform... unix
        no apache given
        no netscape given
        configure: creating ./config.status
        config.status: creating Makefile
        config.status: creating apache-1.3/Makefile
        config.status: creating apache-1.3/Makefile.apxs
        config.status: creating apache-2.0/Makefile
        config.status: creating apache-2.0/Makefile.apxs
        config.status: creating common/Makefile
        config.status: creating common/
        config.status: creating common/jk_types.h
        config.status: creating jni/Makefile
        config.status: creating common/portable.h
        config.status: executing depfiles commands
      3. Edit Edit "native/apache-2.0/Makefile.apxs" and add "-arch x86_64" as described here. Please note that this string needs to be specified twice.
      4. Invoke "make" and "" is generated in "native/apache-2.0" directory.
    3. Copy the generated "" as:

      ~/workspaces/tomcat-connectors-1.2.27-src/native/apache-2.0 >sudo cp /usr/libexec/apache2/
    4. Load the "mod_jk" module in httpd by editing "/etc/apache2/httpd.conf". Please note another similar file exists in "/etc/httpd/httpd.conf" but ignore that one. Add the following as the last "LoadModule" line:

      LoadModule jk_module     libexec/apache2/
    5. Configure "mod_jk" by adding the following lines immediately below the previously "LoadModule" line:

      JkWorkersFile /etc/apache2/
      # Where to put jk logs
      JkLogFile /var/log/httpd/mod_jk.log
      # Set the jk log level [debug/error/info]
      JkLogLevel debug
      # Select the log format
      JkLogStampFormat "[%a %b %d %H:%M:%S %Y] "
      # JkRequestLogFormat set the request format
      JkRequestLogFormat "%w %V %T"
      # Send all jsp requests to GlassFish
      JkMount /\*.jsp loadbalancer

      The key lines in this configuration are the first and the last one. The first line informs "mod_jk" about the location of "" file (explained later). The last line instructs to redirect only JSP requests. This will allow the static content such as images, text files, and media to be served from "httpd" itself.

      Also create the log directory specified in the configuration as:

      sudo mkdir /var/log/httpd
    6. Create a new file "/etc/apache2/". Again, this is not in "/etc/httpd" directory. Use the following contents:

      # Define 1 real worker using ajp13
      # Set properties for instance1
      # Set properties for instance2
      # Set properties for instance3


      Read more about format. Essentially this file is used to load-balance a 3-instance cluster and specify configuration values for each instance. Note that the value of "worker.instanceX.port" for instance X is exactly same as specified during instance configuration earlier.
  6. Copy "tomcat-ajp.jar" from the "lib" directory of the latest Tomcat 5.5.xcommons-logging.jar (version 1.1.1), and commons-modeler.jar (version 2.0.1) to GLASSFISH_HOME/lib. This is done as:

    ~/samples/v2/clustering/glassfish/lib >cp ~/tools/apache-tomcat-5.5.27/server/lib/tomcat-ajp.jar .
    ~/samples/v2/clustering/glassfish/lib >cp ~/Downloads/commons-logging-1.1.1/commons-logging-1.1.1.jar .
    ~/samples/v2/clustering/glassfish/lib >cp ~/tools/commons-modeler-2.0.1/commons-modeler-2.0.1.jar .

    You may have to restart cluster in order for these JARs to be loaded by each instance.
  7. An "httpd" instance is already running on port# 80 in my particular instance of Mac OS X. Instead of mangling with that, I decided to change the listening port for the new instance that will be spawn for out front-end. This can be easily done by editing "/etc/apache2/httpd.conf" and looking for lines similar to:

    Listen 80

    And change "Listen 80" to "Listen 81".
That completes the configuration, phew!

Lets start "httpd" as:

sudo httpd

The "httpd" logs are available in "/private/var/log/apache2". The following message indicates a successful start of the web server:

. . .
[Thu Jan 29 11:14:16 2009] [warn] Init: Session Cache is not configured [hint: SSLSessionCache]
[Thu Jan 29 11:14:16 2009] [warn] No JkShmFile defined in httpd.conf. Using default /usr/logs/jk-run
[Thu Jan 29 11:14:16 2009] [warn] No JkShmFile defined in httpd.conf. Using default /usr/logs/jk-run
[Thu Jan 29 11:14:16 2009] [notice] Digest: generating secret for digest authentication ...
[Thu Jan 29 11:14:16 2009] [notice] Digest: done
[Thu Jan 29 11:14:16 2009] [warn] pid file /private/var/run/ overwritten -- Unclean shutdow
n of previous Apache run?
[Thu Jan 29 11:14:16 2009] [notice] Apache/2.2.9 (Unix) mod_ssl/2.2.9 OpenSSL/0.9.7l DAV/2 mod_jk/1.
2.27 configured -- resuming normal operations

OK, now show time!

If everything has been configured properly as described above then "http://localhost:81/clusterjsp/HaJsp.jsp" looks like:

Enter session attribute as "aaa" and value of the attribute as "111". After you click on "ADD SESSION DATA" button, the updated page looks like:

The highlighted part shows that the request is served from "instance1" and recently added session data. Lets stop "instance1" and see if the promise of high availability is fulfilled :)

Click on "Instances" tab, select "instance1" and click "Stop". The admin console looks like:

Notice "instance1" is shown as stopped. Clicking on "Reload Page" on "http://localhost:81/clusterjsp/HaJsp.jsp" shows:


Even though "instance1" is not runing the session data is still available. And that is possible because of the seamless session failover from primary ("instance1") to the replica partner ("instance2"). The highlighted part indicates that the request is now indeed served by "instance2".

Here are some other useful links to consider:
Please leave suggestions on other TOTD (Tip Of The Day) that you'd like to see. A complete archive of all tips is available here.

Technorati: totd glassfish highavailability clustering loadbalancer mod_jk apache httpd mac leopard

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Arun Gupta is a technology enthusiast, a passionate runner, author, and a community guy who works for Oracle Corp.

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