TOTD #81 explained how to install/configure nginx for load-balancing/front-ending a cluster of Rails application running on GlassFish Gem. Another popular approach in the Rails community is to use Apache HTTPD + mod_proxy_balancer. A user asked the exact details of this setup on the GlassFish Gem Forum. This Tip Of The Day (TOTD) will clearly explain the steps.

1. Create a simple Rails scaffold and run this application using GlassFish Gem on 3 separate ports as explained in TOTD #81.
2. Setup and configure HTTPD and mod_proxy_balancer
1. Setup and install Apache HTTPD as explained here. I believe mod_proxy_balancer and other related modules comes pre-bundled with HTTPD, at least that's what I observed with Mac OS X 10.5.7. Make sure that the "mod_proxy_balancer" module is enabled by verifying the following line is uncommented in "/etc/apache2/httpd.conf":
   
   

   LoadModule proxy_balancer_module libexec/apache2/mod_proxy_balancer.so

   
   Please note another similar file exists in "/etc/httpd/httpd.conf" but ignore that one.
2. Setup a mod_proxy_balancer cluster by adding the following fragment in "httpd.conf" as:
   
   

   <Proxy balancer://glassfishgem> BalancerMember http://localhost:3000 BalancerMember http://localhost:3001 BalancerMember http://localhost:3002 </Proxy>

   
   The port numbers must exactly match with those used in the first step.
   
3. Specify the ProxyPass directives to map the cluster to a local path as:
   
   

   ProxyPass / balancer://glassfishgem/ CustomLog /var/log/glassfishgem.log/apache_access_log combined

   
   The "/" at the end of "balancer://glassfishgem" is very important to ensure that all the files are resolved correctly.
4. Optionally, the following directive can be added to view the access log:
   
   

   CustomLog /var/log/glassfishgem.log/apache_access_log combined

   
   Make sure to create the directory specified in "CustomLog" directive.
3. Now the application is accessible at "http://localhost/runlogs". If a new GlassFish instance is started then update the <Proxy> directive and restart your HTTPD as "sudo httpd -k restart". Dynamic update of BalancerMembers can be configured as explained here.

TOTD #81 started the Rails application in root context. You can alternatively start the application in a non-root context as:

~/tools/jruby/rails/runner >../../bin/jruby -S glassfish -e production -c myapp Starting GlassFish server at: 10.0.177.178:3000 in production environment... Writing log messages to: /Users/arungupta/tools/jruby-1.3.0/rails/runner/log/production.log. Press Ctrl+C to stop. . . . ~/tools/jruby/rails/runner >../../bin/jruby -S glassfish -e production -c myapp -p 3001 Starting GlassFish server at: 10.0.177.178:3001 in production environment... Writing log messages to: /Users/arungupta/tools/jruby-1.3.0/rails/runner/log/production.log. Press Ctrl+C to stop. . . . ~/tools/jruby/rails/runner >../../bin/jruby -S glassfish -e production -c myapp -p 3002 Starting GlassFish server at: 10.0.177.178:3002 in production environment... Writing log messages to: /Users/arungupta/tools/jruby-1.3.0/rails/runner/log/production.log. Press Ctrl+C to stop.

and then the ProxyPass directive will change to:

ProxyPass /myapp/ balancer://glassfishgem/myapp/

The changes are highlighted in bold. And the application is now accessible at "http://localhost/myapp/runlogs".

After discussing on Apache HTTP Server forum, the BalancerMember host/port can be printd in the log file using a custom log format. So add the following log format to "/etc/apache2/httpd.conf":

LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-agent}i\" \"%{BALANCER_WORKER_NAME}e\"" custom

And change the format from the default "combined" to the newly defined "custom" format as:

CustomLog /var/log/glassfishgem.com/apache_access_log custom

Three subsequent invocations of "http://localhost/runlogs" then prints the following log entries:

::1 - - [17/Jun/2009:10:53:53 -0700] "GET /runlogs HTTP/1.1" 304 - "-" "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.0.11) Gecko/2009060214 Firefox/3.0.11" "http://localhost:3002" ::1 - - [17/Jun/2009:10:54:04 -0700] "GET /runlogs HTTP/1.1" 200 621 "-" "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.0.11) Gecko/2009060214 Firefox/3.0.11" "http://localhost:3000" ::1 - - [17/Jun/2009:10:54:05 -0700] "GET /runlogs HTTP/1.1" 304 - "-" "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.0.11) Gecko/2009060214 Firefox/3.0.11" "http://localhost:3001"

As evident from the last fragment of each log line, the load is distributed amongst three GlassFish Gem instances. More details on load balancer algorithm are available here.

Feel free to drop a comment on this blog if you are using GlassFish in production for your Rails applications. Several stories are already available at rubyonrails+glassfish+stories.

Technorati: glassfish rubyonrails apache httpd mod_proxy_balancer loadbalancing clustering