Enabling DNS clustering on cpanel server
First, you will need to enable DNS clustering via each server’s WHM interface.
You will need to sync each web server to its DNS servers.
You do not need to link dedicated DNS servers to each other, or link dedicated web servers to each other.
You should not set a DNS server to sync data back to a web server, as this will put extraneous data on the web server. 
Steps:
   1. Navigate to WHM’s Configure Cluster screen.
   2. Click Enable Dns Clustering.
   3. Click Change.
   4. Click Return to Cluster Status. 
DNS clustering is now enabled. Next, you will need to specify which server(s) you wish to cluster, or share DNS information with.
				 
								
			 	
					
				
				
					The Cpanel Key Server said returned 500 Request Denied - No license entry found
To resolve this issue.  
Run the following script as root:
You will need to Shell (SSH) into your server and type the following;
/usr/local/cpanel/cpkeyclt
 
				 
								
			 	
					
				
				
					From time to time the RubyGems repository will be unavailable. If at any point during installation process the RubyGems repository becomes unavailable, you will need to re-run 
Since Ruby on Rails uses its own web server, it has to run this web server on an alternate port. This causes an issue if you are running a firewall on your system. You will need to ensure that ports 12001 and up are open. We recommend making the max number of the open ports 12001 plus whatever the number of Ruby applications you expect to be running will be.
				 
								
			 	
					
				
				
					Cpanel Install and Licence
You may install cPanel without a license, however it will not be usable until you obtain a license.
Also you need the public ip address of the machine that you plan on running cPanel on.
You can get this address by running the below command if you have lynx installed.
lynx -dump http://www.cpanel.net/showip.cgi
 
If you don’t have lynx installed and are directly connected to the internet, you can use the below command:
/sbin/ifconfig eth0 |grep inet | awk ‘{print $2}’ | awk -F: ‘{print $2}’
 
-dump  dumps  the  formatted  output  of  the default document or those specified on  the  command  line  to  standard  output. Unlike interactive mode, all documents are processed.  This can be used              in the following way:
lynx -dump http://www.subir.com/lynx.html
 
				 
								
			 	
					
				
				
					Installing Ruby
To begin, you will need root access to the server on which you wish to install Ruby
Requirements 
cPanel version 11.
Log into your server as the root user and issue the following command via the command line: 
Execute the following script to install Ruby: 
After installing Ruby, you will need to make sure that the appropriate ports are opened for your cPanel users. 
By default, Ruby applications begin on port 12001. Ruby application port numbers are automatically incremented with each new Ruby application. 
This means the the first Ruby on Rails application created on your server will use port 12001, while the second Ruby on Rails application will use port 12002.