Wednesday, June 22, 2016

My Transition To UNIX From DOS: Working With Aliases


It's been fun playing on a Windows OS machine as a Software Engineer. I always find it interesting and fun to explore other things. Funny enough though, I have always been scared of using commands because I always felt that I would mess up something on my machine and have to do a factory reset of some sort. It's always a drag when one has to do that on their work machine. Finally I landed at a place where the recommended OSes were the unix based ones, preferably, Linux Ubuntu or Macintosh OS. Ultimately I went for the Macintosh OS, just because... 

From my first day there I had to learn some basic and common unix commands from the likes of: tail -f /file/path/here up to, ssh At some point I got a bit fed up with typing a long and same old command everyday and to a point, every hour even. Even though it was great practice, something had to be done and that's when I learned about Unix aliases. Aliases are pretty much abbreviations of FUCs "Frequently-Used Commands" 

For example one can shorten a command like: defaults write AppleShowAllFiles NO, which toggles hidden files & folders off, in Mac OS's finder, to something like show-hidden-files which will essentially be the name "Alias" of that command. 

Now to the "Nuts & Bolts", we will look at the following:
  1. Creating / Adding a new alias
  2. Referencing an external file for aliases.
We will also need some "shell scripting skills", nothing major, very few lines of code so that's all fun and well

1. Creating / Adding a new alias

Perhaps this may be slightly different on other unix platforms, so this is more pertinent to Mac OS. Let's go...!
  • Open finder and head to your home directory. (Unless you are in your home directory by default) 
  • Look for a file named, ".bash_profile". Notice the dot before the file name. If you cannot see hidden files then use the command (in your terminal)  from the example above and just change that "NO" to "YES". Then hold down the "alt" button and then "alt-click (right-click)"  on the finder icon and then "left click"  the option "Relaunch".
  • Go back to looking for our file and then open it in any of your favourite text editor... (Sublime Text, Atom, even VI on your terminal etc ...)
  • Let's add a new line, this will be a new alias for any command you want to add, for example:  

  alias show_files_no="defaults write AppleShowAllFiles NO"

  • To delineate things a bit more, "alias" is a reserved key word for shell, so you are letting shell know that you want to add a new alias, the next word "show_files_no" can be anything you want, this is the actual name or alias of your command. Then last part "defaults write AppleShowAllFiles NO" is the actual shell command that you would normally type and execute on the terminal. We are almost done. 
  • If you were editing the file using the terminal with VI, VIM, Nano etc... The next thing is to reload the ".bash_profile"  by either closing and opening the terminal again or typing the command "bash -l". I believe there may be more commands out there that one can use. 
  • Finally open terminal if you closed it. If you reloaded the ".bach_profile"  using the command then just type the alias you added recently, in our case just type "show_files_no". This will execute the command associated with that alias. To see if this made an effect just follow the steps about relaunching finder above. That's it!

2. Referencing an external file for aliases.

I have recently been playing around with externalising some bash profile stuff because I have a lot of aliases and my bash profile artifact was just getting too congested. So main things to note here is that
... you don't have to create your new external file inside the same directory as your bash profile and the name of your file does not have to start with the word "bash"...
I just named it that way for the sake of naming it that way! So let's get to it:
  • Create a new file as follows, "~/bashes/.whatever_file_name", of which in my case, is inside a new folder that I created, "bashes", in my home directory and named it ".bash_aliases". Keep in mind that your folder can be named anything you want.

  • Now go back to your main file, ".bash_profile" and then replace your alias with the following shell scrip code.

  #Referencing path to file containing the aliases
  if [ -f $aliasesPath ]; then 
     source $aliasesPath

  • Something along those lines should help you out. It's basically a shell if statement that checks if that file path exists and if so we then reference it from the main ".bash_profile" so next thing you should try is to now reload like we did earlier if you did all this using terminal or just close and then open terminal.  
So now you have externalised the aliases and you can try with other stuff like your environment variable profiles can also be externalised and so forth. Like I said this is the first main thing I learned when moving to UNIX, I hope it helps someone out there. I would really love to learn from you on how I can improve this post and some feedback, Cheers! 

Tuesday, February 11, 2014

Starting with Acitiviti (BPM Engine)


I am busy working on a project which has a very small workflow or business process component to it. One of the requirements was that we had to use Activiti to manage the business processes. My first port of call was the "Activiti in Action" book. When I felt that had enough ammunition to take on Activiti, I gave it a go.

There were a few bumps along the road especially because I was trying to incorporate Acitiviti into an existing Spring Maven application. In this blog I am going to show you how to get your Activiti code running in a Maven Spring application.

Activiti Architecture

The Basic Activiti architecture is pretty simple. There is a database which is used to maintain and persist state. You can manipulate the state of objects within the database by using the Activiti engine or API. This can be the Activiti libraries or dependencies in your application or you can also interrogate the database using the Rest services.

The Activiti Explorer is a web application which uses the API to view and change objects housed in the database. The Activiti Explorer also has a tool (Activiti Modeler) which can be used to model BPMN processes. You can model your process using this tool and then export the configuration into an xml file. You can then use this xml file in your application without having to model the process manually. 


You will need to download Tomcat and the latest Activiti Release. The only 2 artefacts of concern to you for this tutorial can be located in the wars directory:
  • activiti-rest.war
  • activiti-explorer.war 
You can deploy these 2 war files on your Tomcat server. To be really specific, you only need the activiti-explorer. You might need to add the H2 database Driver to your Tomcat server.

Do I need a database?

Activiti does use a database but you do not need one explicitly. Activiti is packaged with an embedded H2 database. This means that when you run the application, it will access this embedded database automatically. So even though you are not specifying a database, there is one being used.

Add these dependencies to your Maven POM file

     <!-- Activiti Stuff-->  
 <!-- Spring Stuff-->  
 <!-- H2 Driver-->  

Add this repository to your Artefact repository or your Maven POM file

       <id>Alfresco Maven Repository</id>  

Design a Simple Activiti Workflow process using Activiti Modeler

This is the sample process that I designed. It is simple and self explanatory.
Here is the exported xml file contents (SampleActivitiProcess.bpmn20.xml):
 <?xml version="1.0" encoding="UTF-8"?>  
 <definitions xmlns="" xmlns:xsi="" xmlns:activiti="" xmlns:bpmndi="" xmlns:omgdc="" xmlns:omgdi="" typeLanguage="" expressionLanguage="" targetNamespace="">  
  <process id="SampleActivitiProcess" name="SampleActiviti" isExecutable="true">  
   <startEvent id="start" name="start"></startEvent>  
   <userTask id="SomeUserTask" name="SomeUserTask"></userTask>  
   <endEvent id="end" name="end"></endEvent>  
   <sequenceFlow id="flowFromStart" name="flowFromStart" sourceRef="start" targetRef="SomeUserTask"></sequenceFlow>  
   <sequenceFlow id="flowToEnd" name="flowToEnd" sourceRef="SomeUserTask" targetRef="end"></sequenceFlow>  
  <bpmndi:BPMNDiagram id="BPMNDiagram_SampleActivitiProcess">  
   <bpmndi:BPMNPlane bpmnElement="SampleActivitiProcess" id="BPMNPlane_SampleActivitiProcess">  
    <bpmndi:BPMNShape bpmnElement="start" id="BPMNShape_start">  
     <omgdc:Bounds height="30.0" width="30.0" x="165.0" y="210.0"></omgdc:Bounds>  
    <bpmndi:BPMNShape bpmnElement="SomeUserTask" id="BPMNShape_SomeUserTask">  
     <omgdc:Bounds height="80.0" width="100.0" x="301.0" y="185.0"></omgdc:Bounds>  
    <bpmndi:BPMNShape bpmnElement="end" id="BPMNShape_end">  
     <omgdc:Bounds height="28.0" width="28.0" x="495.0" y="211.0"></omgdc:Bounds>  
    <bpmndi:BPMNEdge bpmnElement="flowFromStart" id="BPMNEdge_flowFromStart">  
     <omgdi:waypoint x="195.0" y="225.0"></omgdi:waypoint>  
     <omgdi:waypoint x="301.0" y="225.0"></omgdi:waypoint>  
    <bpmndi:BPMNEdge bpmnElement="flowToEnd" id="BPMNEdge_flowToEnd">  
     <omgdi:waypoint x="401.0" y="225.0"></omgdi:waypoint>  
     <omgdi:waypoint x="495.0" y="225.0"></omgdi:waypoint>  
I would advise you to always change the ID's of all of the elements and also provide them with descriptive names. This helps you out tremendously when developing against your BPMN process.

Let us start Coding

The general process of running an Activiti process is as follows:

Design BPMN Process

You can use Activiti Modeler from Activiti Explorer, the Eclipse Activiti Plugin or manually build the xml representing your business process flow.

Deploy Process

You can use Activiti Explorer to deploy or programatically deploy your business process flow. Doing it programatically, you have 2 options:

  • The Spring way
  • The Standard java way

Run Process Instance

You reference a process which is deployed and start a new process instance.

Create Activiti process engine

The are 3 ways to achieve this:

In Memory

 ProcessEngine processEngine = ProcessEngineConfiguration  

This is the easiest and fastest way to get up and running. It references the embedded database and uses the default configuration.

File based

 ProcessEngine processEngine = ProcessEngineConfiguration.createProcessEngineConfigurationFromResource("activiti.cfg.xml").buildProcessEngine();  
The database connection settings are referenced from the activiti.cfg.xml

Here is a sample file refencing the embedded default H2 database:
 <?xml version="1.0" encoding="UTF-8"?>  
 <beans xmlns=""  
   <!--<bean id="processEngineConfiguration"  
   <bean id="processEngineConfiguration" class="org.activiti.engine.impl.cfg.StandaloneProcessEngineConfiguration">  
     <property name="jdbcUrl"  
          value="jdbc:h2:/tmp/activiti;AUTO_SERVER=TRUE" />  
     <property name="jdbcDriver" value="org.h2.Driver" />  
     <property name="jdbcUsername" value="sa" />  
     <property name="jdbcPassword" value="" />  
     <!-- Database configurations -->  
     <property name="databaseSchemaUpdate" value="true" />  
     <!-- job executor configurations -->  
     <property name="jobExecutorActivate" value="false" />  
     <!-- mail server configurations -->  
     <property name="mailServerPort" value="5025" />  
     <property name="history" value="full" />  

Basic Spring Style

     ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("Service-core-application-context.xml");  
     ProcessEngine processEngine = (ProcessEngine) ctx.getBean("processEngine");  

Here is the Spring configuration required:
   <bean id="dataSource" class="org.springframework.jdbc.datasource.SimpleDriverDataSource">  
     <property name="driverClass" value="org.h2.Driver" />  
     <property name="url" value="jdbc:h2:mem:activiti;DB_CLOSE_DELAY=1000" />  
     <property name="username" value="sa" />  
     <property name="password" value="" />  
   <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">  
     <property name="dataSource" ref="dataSource" />  
   <bean id="processEngineConfiguration" class="org.activiti.spring.SpringProcessEngineConfiguration">  
     <property name="databaseType" value="mysql" />  
     <property name="dataSource" ref="dataSource" />  
     <property name="transactionManager" ref="transactionManager" />  
     <property name="databaseSchemaUpdate" value="true" />  
     <property name="deploymentResources"  
          value="classpath*:SampleActivitiProcess.bpmn20.xml" />  
     <property name="jobExecutorActivate" value="false" />  
   <bean id="processEngine" class="org.activiti.spring.ProcessEngineFactoryBean">  
     <property name="processEngineConfiguration" ref="processEngineConfiguration" />  
   <bean id="repositoryService" factory-bean="processEngine" factory-method="getRepositoryService" />  
   <bean id="runtimeService" factory-bean="processEngine" factory-method="getRuntimeService" />  
   <bean id="taskService" factory-bean="processEngine" factory-method="getTaskService" />  
   <bean id="historyService" factory-bean="processEngine" factory-method="getHistoryService" />  
   <bean id="managementService" factory-bean="processEngine" factory-method="getManagementService" />  
You can see in this way, Spring handles deploying the BPMN Process for you.

It is important to know that BPMN Process xml files can only be of 2 types and have to end in the following extensions for the API to process / deploy the files:

  1. .bpmn20.xml (Activiti Modeler)
  2. .bpmn (Eclipse Activit Plugin)
The 2 services that we require is the RuntimeService and the RepositoryService:
 RepositoryService repositoryService = processEngine.getRepositoryService();  
 RuntimeService runtimeService = processEngine.getRuntimeService();  

Remember that if you are using the Spring way, the respective beans already exist.
We use the RepositoryService to deploy the process, if it has not already been done (the spring way or via the Activiti Explorer console):

We then start a process using the RuntimeService:
 String procId = runtimeService.startProcessInstanceByKey("SampleActivitiProcess").getId();  

A process is considered to be active if it is not in an end state or not suspended. You can use the Task Service to manipulate active tasks:
 TaskService taskService = processEngine.getTaskService();  
 List<Task> tasks = taskService.createTaskQuery().active().list();  
Remember that the TaskService bean already exists if you are using the Spring way.

You can use the TaskService to query, claim and complete tasks:
 taskService.claim(task.getId(), "sampleUser");  

Once the Process in a Final state, you can't use the TaskService for these processes but need to use the HistoryService:
 HistoryService historyService = processEngine.getHistoryService();  
     HistoricProcessInstance historicProcessInstance =  
     System.out.println("Process instance end time: " + historicProcessInstance.getEndTime());  
Remember that the HistoryService bean already exists if you are using the Spring way.


This should be enough information to get you up and running with Activiti. Remember to start off small and build on incrementally. This way you can understand the process in much greater detail.
Activiti is a great tool and what is even more amazing is that this piece of software is open source and free to use.

As always, I would love to hear your comments or questions. You can also follow me on Twitter or Google plus. I have added shortcuts to my profile in the About me link.

Tuesday, January 21, 2014

Back to Java Basics - Installing Java

I can't remember learning how to install java at varsity. Maybe, the instructions were on the first tutorial and I never had to bother with it again or it might have just been installed for us. The point being; when I started at my first job and had to install java on both my Windows machine and my allocated workspace on a Unix, I just could not get it right.

Was I crazy?

This might have been the case but then again whenever I feel an inference in the direction that I am crazy, I often find solace in believing that everyone else in this world is crazy and I being the only sane one. Moving on ... I did google the usual "How to install java on windows" and followed the instructions meticulously but still it did not work. You can imagine how I felt when I had to ask one of the seniors to help me install java. It was not straight forward for him as well. He spent about 30 minutes to an hour. Messing around with environment variables through command line and all kinds of weird nonsense. Eventually he got it working and I was amazed. My first thoughts were that if getting java installed was so difficult, how would I cope as a java developer? It turned out that the windows machine I inherited belonged to a techie who installed every possible software he could get his hands on. You might be asking: but this has nothing to do with installing java???

Oh, you are so wrong. I eventually got to understand the sorcery behind installing java. Up to this day I still find senior java engineers struggling with this concept but in a different problem space. As a practising consultant we often have to work with systems that are running in production with multiple versions of java installed but running some undesired version. I have seen even the most senior engineers spending hours trying to sort this mess out.

By contrast to the title, I am not going to show you how install java. I am going to clear up all the mystery that surrounds:
  • Installing java step by step and it just not working for you
  • Having installed a specific version of java but when running "java -version" it says that it is running some other obscure version

Understand Environment Variables

It is of utmost importance that you understand how environment variables work. I have written an article and would suggest that you read this article very carefully and become comfortable with the concepts before proceeding:

Setting Environment Variables on Unix and Windows

If you reached this point, you are really comfortable with environment variable ;-)
Cool, let us continue...

Installing Java

For me there are just 3 important parts to installing java:

  1. The jdk package (jdk folder)
  2. Setting the JAVA_HOME environment variable
  3. Updating the path variable to reference the jdk binary or executables

Point number 2 is not even required, you will understand later.

Once you have the jdk package (folder containing bin, include, jre, lib & Other files) you are 90% there. If you type java through a command line at this point, unfortunately java will not work. The only thing required here is to get the operating system to reference the java binary or executables. If you have read my other post, you should have realised that I am talking about setting the path variable. All we need to do is add the path / location of the bin directory to the path environment variable.

Now, if you try and run java from a command line it should work. If you have followed my instructions correctly and it is still not working then; open up a new command line terminal (fully explained in my other post) or this is were things get really interesting.

Why is the JAVA_HOME environment variable not important? 

The JAVA_HOME environment variable would contain a reference to the base directory of jdk. When setting the path, it is advised that you only add JAVA_HOME/bin so that the operating system can find the binaries executable files. There is no functional difference by specifying the full directory path to the bin directory. It is merely a standard and preferred convention.

Why the convention?

The convention is there so that if you reference an alternate version of java, you would only need to update the JAVA_HOME environment variable. The path variable is quite long containing multiple references to different executable files. It can become "difficult" working with this long string and a typo can affect some other program.
So in a nutshell, the JAVA_HOME environment variable is a convenience variable for the purposes of this article. For your broader knowledge, the JAVA_HOME environment variable might be referenced by programs that require java. Certain web servers or application servers might need this variable be set in order for it to function. It uses this variable to reference libraries or files for it to function correctly.

Installing java today(The Interesting part I spoke about earlier)

I have noticed that when you download a java jdk today, it is packaged with an installation procedure. This procedure completes the process mentioned above on your behalf but even if you use the installer, you might still not get java to work or an undesired version might be running.

Other programs mess with the path variable 

There are so many programs, applications, servers and processes that require java. When installing them, they either reference the java installation already installed on your machine (good program) or contain it's own minimised / customised jdk or jre. If they are installed and append to your path variable, you are done! What happens is that every time you run a java comand, the system evaluates the path variable from left to right and looks in each directory for an executable called java. It will find the first occurrence, which in this scenario is a minimised / customised program specific one execute and terminate. I have personally been bitten by this when installing Oracle server and even some profiling tools.
How do we fix this?
I specifically highlighted, bolded, increased font size and underlined the word "add" earlier in this post. When most people hear add they think that it is append(put at the back). You can even prepend(put in the front) the path variable. This is a very cool trick. Now you have a way of guaranteeing that your desired java executable is executed first. Prepending the path variable saves you from figuring out which reference is problematic. You can figure this out by removing the references one at a time up until you get it working.


The path variable can be a source of major headaches but if you understand both environment variables really well and what is required to install java you should be fine. You would also be comfortable hosting multiple versions of java and be able to reference a specific version if and when required by merely changing your JAVA_HOME environment variable.

As Always, I would love to hear your comments or suggestions on how I can improve this post. I am also more than willing to lend a hand if you are having issues in your environment!

Wednesday, January 8, 2014

Setting Environment Variables on Unix and Windows

In this post I will try and explain the different ways on how to set environment variables on both Windows and Unix operating systems. I am also going to address the scope when setting an environemt variable.

What environment variables are set on my machine?

You can easily check this by typing "set" into a command line terminal on both windows or unix.
Unix and windows:
How do you retrieve the value of a particular environment variable?
echo $environment_variable
echo %environment_variable%

What are environment variables?

Environment variables are operating system level variables that can affect the running of a process. This meaning is slightly obscure but let me try to explain it the way I understand it. The way I see it, environment variables are just aliases for file or directory paths. All they are are just short names or references to a directory on your system. The reason for their existence as you may have realised by now is that they are dynamic and are uniformly used in programs (ie. no hard coding paths).

There is however one special environment variable. This is the "path" variable. The path variable contains multiple directory locations separated by either a ";" on windows or ":" in unix. Each directory location references a program's binary files or executable files. As an example, if you were to type in "java" on the command line interface of both windows or unix, the OS would search each of the directories in the path variable and identify the executable or binary with the name java. When it identifies the executable matching the name, it will execute the process and terminate. This is a very interesting and important statement.

  1. The path variable is evaluated from left to right scanning each directory for an executable matching the name.
  2. It executes the first occurrence of the executable and terminates.
  3. If no matches are made, a command not found message is returned.

How to set environment variables? 

Environment variables can be set either programmatically or manually with both being equal but they can be set for different levels of scope.

Global Scope

This is the highest level and is available to all users of the system. 
On unix this can be achieved by adding the environment variable to /etc/profile or /etc/profile.d file. On windows you can set this by going to the properties of "My Computer" and then selecting the environment variables tab. Within this tab, you should see the System variables and User Variables. Set a System Variable.
You will only be able to set a variable on this level if you are an administrator on the system.  

Once an environment variable is set, you would need to restart any open command terminals for the change to take effect. If you were to restart your machine the variable would still be there. It is permanent.

User Scope

Environment variables set at this level is only available to the user that is logged in.
On unix this can be achieved by adding the environment variable to /Users/<username>/.bash_profile file. Once an environment variable is set, you would need to log in again for the change to take effect or you can execute the .bash_profile script which will set the environment variable for the open session.

On windows you can set this by going to the properties of "My Computer" and then selecting the environment variables tab. Within this tab, you should see the System variables and User Variables. Set a User variable.
Once an environment variable is set, you would need to restart any open command terminals for the change to take effect. If you were to restart your machine the variable would still be there. It is permanent for the user.

Session Scope

Environment variables set at this level only last for the duration that the command line terminal is open. It is lost as soon as the terminal is closed.
On unix this can be achieved by typing the following in a command line terminal: 
export VARIABLE=value  # for Bourne, Bash and related shells
setenv VARIABLE value  # for csh and related shells
On windows this can be achieved by typing the following in a command line terminal:

Script Scope

Environment variables set at this level only last for the duration that the script runs. It is lost as soon as the script terminates, unless the script is executed from command line terminal. In this case the session scope rules apply.
Same as in the session scope but is embedded in a shell or batch script.

Setting the "path" environment variable

All of the above applies to normal environment variables. Remember we said that the "path" variable is special and contains multiple directories. You can edit the path environment variable in the same way as mentioned for normal variables as above for the most part. 

Here are other variations which might be useful when setting the "path" environment variable.
When setting on windows use the ";" symbol as a separator:
SET path=C:/interesting/informing/techies;C:/important/informing/techies
When setting on unix use the ":" symbol as a separator:
export path=/interesting/informing/techies:/important/informing/techies
If you wanted to append or prepend a new directory location to the existing "path" environment variable:      
When setting on windows use the %VAR% notation:
SET path=%path%:C:/interesting/informing/techies;C:/important/informing/techies
When setting on unix use the $VAR notation:
SET path=$path:/interesting/informing/techies;/important/informing/techies

Remember prepending or appending to the path variable makes a huge difference!!!

Who uses and maintains environment variables?

Applications and programs use environment variables. They also maintain the environment variables by doing the necessary creations, deletions and updates during installation, updating and uninstalling processes. 

Therefore, messing around with environment variables without a clear and proper understanding can cause your system not to work as desired. My suggestion is that if you do want to test something out, try it out on the session scope. In this way your system is not permanently affected. 

With this said, you can also use environment variables in your applications. They are great at abstracting paths and are also a solution to hard coding. 


I hope that this gives you a clear understanding of environment variables and their scope. As always, I would appreciate any feedback and comments are always welcome.

If you have issues in your environment I am more than happy to lend a hand!

Wednesday, December 4, 2013

Installing mysql database on a unix/linux box

There are a few tricks involved with installing mysql on a unix machine. There is the installation part and then the part where you need to connect to the mysql database server.

PS. This article assumes that the unix machine has internet access.

Step 1

Download and install mysql database server.
This command will download mysql server from the internet and install it.
If you have root access:
 yum install mysql-server  
If you do not have root access:
 sudo yum install mysql-server  

Step 2

Start the mysql database server as a unix service.
If you have root access:
 service mysqld start  
If you do not have root access:
 sudo service mysqld start  

Step 3

Check the status of the mysql database server.
If you have root access:
 service mysqld status  
If you do not have root access:
 sudo service mysqld status  

Step 4

Check that you can connect to the mysql database from the same machine.
 shell>mysql -u root  
Then run a simple query:

Step 5

Secure your mysql database server.
Run this shell command on the server:
This is an important script. It allows you to set the root password which we need to do and other tasks like removing anonymous access.
You can re-perform step 4 but this time remember to supply your password:
 shell>mysql -u root -p<password>  

Step 6

Check that you can connect to the mysql database from the same machine.
 shell>mysql -u root -p<password>  
Then run a this query:
 GRANT ALL PRIVILEGES ON *.* TO 'root'@'%'  
   IDENTIFIED BY PASSWORD 'your_password'  
The query allows remote access from any location where the user is root and the password. You can replace % with a hostname or ip address. You can also use it as a wildcard.
Remember to flush privileges:

Step 7

Use mysql workbench to connect to the mysql database server.

Additional Notes

Shut Down the mysql database server.
If you have root access:
 service mysqld stop  
If you do not have root access:
 sudo service mysqld stop  

Leave a comment if you feel that there is anything that I have left out.

Friday, November 29, 2013

Creating a Simple JBoss Cluster (7.1.1 final)


I will be demonstrating the tasks required to create a simple JBoss Cluster environment on a single machine. I will be using jboss-as-7.1.1.Final for this demonstration.

The Cluster is going to contain the following:
  • The complete Cluster is going to be hosted on one physical machine
  • The Master and Slave will each contain 3 server instances(Server 1, 2 & 3)
  • The Master instance will act as the Domain Controller
  • The Slave instance will act as a Host
  • The 3 server instances on both Master and Slave will be part of 2 Server Groups
  • Server 1 & 2 on both Master and Slave will be part of one Server Group
  • Server 3 on both Master and Slave will be part of one Server Group
  • The Server Group hosting Server 1 & 2 on both Master and Slave will not be Cluster-able but will be Domain Controlled
  • The Server Group hosting  Server 3 on both Master and Slave will be Cluster-able and Domain Controlled  
Here is a diagram illustrating the Design Architecture:

Why do we need a Cluster

  • High availability
  • Load balancing
  • Failover
  • Session Replication
  • Scalability


Download the jboss-as-7.1.1.Final package
Extract the contents of the package to 2 different directories. One directory called Master and the other called Slave.

Configuring the Master Server (Domain Controller)


Edit the file:

Replace with the IP address of the machine hosting Master in the following location:
   <interface name="management">  
     <inet-address value="${}"/>  
   <interface name="public">  
     <inet-address value="${jboss.bind.address:}"/>  
   <interface name="unsecured">      
     <inet-address value="" />    
We need to change this so that:
  1. The management interface ensures that Slave can connect to Master
  2. The public interface allows the application to be accessed from external addresses
  3. The unsecured interface allows RMI calls

Create 2 ManagementRealm user accounts for domain management authentication 

Execute the add-user script in the bin directory

User Account 1
UserName: admin
Password: password
Realm: ManagementRealm

User Account 2 - This user allows the Slave server to connect to the Master Server
UserName: slave
Password: password
Realm: ManagementRealm

For some reason JBoss enforces security checking on the Hornet queues. I don't know if this is intentional or a bug. You can supply any username and password even though you have not configured it anywhere and it does not even exist. My suggestion is to disable security.

Edit the file:


This needs to be updated in 2 locations of the domain.xml file:
 <subsystem xmlns="urn:jboss:domain:messaging:1.1">  
Change the Server Group profile configuration:
 <server-group name="other-server-group" profile="full-ha">  
       <jvm name="default">  
         <heap size="64m" max-size="512m"/>  
       <socket-binding-group ref="full-ha-sockets"/>  
Our Clustered Server group is called other-server-group. Change the profile and socket binding group reference as above. The profile is used for configuration related to Modules. These Modules are enabled and bound in the socket binding group. We need to specify a profile and socket binding group that supports Clustering.
The following modules are required:
  • infinispan
  • jgroup
  • mod_cluster
The reason we need to change this from the default configuration is because this version of JBoss has a bug that does not allow Clustering using the default value.

Update the domain.xml file:

 <subsystem xmlns="urn:jboss:domain:modcluster:1.0">  
         <mod-cluster-config advertise-socket="modcluster" proxy-list="<IP Address of Master>:10001">  
             <load-metric type="busyness"/>  
 <subsystem xmlns="urn:jboss:domain:web:1.1" default-virtual-server="default-host" instance-id="${}" native="false">  

This configuration ensures that JBoss is aware of mod_cluster and is publishing or advertising Server Status information to our mod_cluster.

Configuring the Slave Server (Host)


Delete the file:


Edit the file:


Set the host name on Slave by changing:
 <host name="master" xmlns="urn:jboss:domain:1.2">  
 <host name="slave" xmlns="urn:jboss:domain:1.2">  

Configure the Domain Controller as follows(Take note of the Security Realm configured):
     <remote host="<IP Address of Master>" port="9999" security-realm="ManagementRealm"/>  

Replace with the IP address of the machine hosting Slave in the following location:
   <interface name="management">  
     <inet-address value="${}"/>  
   <interface name="public">  
     <inet-address value="${jboss.bind.address:}"/>  
   <interface name="unsecured">      
     <inet-address value="" />    
The same reasons apply here as when we configured for the Master instance above.

Change the Security Realm to the following:
       <security-realm name="ManagementRealm">  
    <secret value="cGFzc3dvcmQ="/>  
           <properties path="" relative-to="jboss.domain.config.dir"/>  
This server identities created allows the Slave instance to connect to Master. We configured the host name of this instance to "slave". This needs to correspond to a user account created on Master with the same user name. From above this corresponds to User Account 2. The secret value is the password of User Account 2 (slave) in base64 format / encoded.

Change the port numbers on the management address to avoid port conflicts with Master:
       <native-interface security-realm="ManagementRealm">  
         <socket interface="management" port="${}"/>  
       <http-interface security-realm="ManagementRealm">  
         <socket interface="management" port="${}"/>  
Increment by 10 000 for convenience purposes.

Add a port offset to Server 1, 2 & 3 to avoid port conflicts with Master:
     <server name="server-one" group="main-server-group">  
       <socket-bindings port-offset="1000"/>  
     <server name="server-two" group="main-server-group" auto-start="true">  
       <socket-bindings port-offset="1150"/>  
     <server name="server-three" group="other-server-group" auto-start="false">  
       <socket-bindings port-offset="1250"/>  
Increment by 1 000 for convenience purposes.

Start Master and Slave

 ./ -b <IP Address of Master> -bmanagement <IP Address of Master>  

 ./ -b <IP Address of Slave> -bmanagement <IP Address of Slave>  

Sample Web Application

Create a very simple web application. You will need to add the distributable tag to the applications web.xml file to configure it to be Cluster-able (Session Replication).
I also suggest that you add System.out.println statements into your application especially in the event of a page being requested. In this way you will be able to easily identify which server is serving your request when running in Cluster mode.

Cluster Administration

You can access the JBoss administration console of the Domain Controller by going to this link:
 http://<IP Address of Master>:9990  
Start up Server 3 on both Master and Slave. Server 3 on both Master and Slave are part of other-server-group while Servers 1 & 2 on both Master and Slave are part of main-server-group. We are only concerned with other-server-group to demonstrate the Clustering concept.

Deploy the Web application to the other-server-group

Make sure that the deployment succeeded. If all was successful, you can access the web application on Master and Slave explicitly.
 http://<IP Address of Master>:8330/cluster-demo/  
 http://<IP Address of Slave>:9330/cluster-demo/  

(Please note that cluster-demo was a Sample Web application which I downloaded from github. Specify the context root to your own application)

If you reached this point the, you have setup a Domain controlled Multi-Server environment. Our next step is to Cluster.


If you were to access any of the server instances in the other-server-group hosting the web application, you would need to specify explicitly the ip address and port number of that particular instance. This means that if were to use the full potential behind Clustering we would need some "unified" address which would hide the Domain Server structure. This central point would then need to route requests to servers participating in the cluster. I think of it as some sort of a proxy or delegator speaking loosely. I have heard people calling it a load balancer. That is true to some degree but, remember it does more that just load balancing. It is also intelligent enough to only route requests to servers that are up and running.

We use the Apache Mod_Cluster to achieve all of the above. The Apache Mod_Cluster is an http daemon. I am using Mod_cluster version 1.2.6. I have never used this tool before and I had to wrap my head around a few concepts before understanding how it actually works.

Download the package meant for your specific operating system.

Extract the contents into the /opt directory. I found that the scripts do not work well if you do not extract it into this directory. You would also need root or sudo access. I found that it modifies files that not accessible by default to basic users.

Configure the httpd.conf file

Here a Sample file that you can use. You would only need to specify your IP Address:
 # This is the main Apache HTTP server configuration file. It contains the  
 # configuration directives that give the server its instructions.  
 # See <URL:> for detailed information.  
 # In particular, see  
 # <URL:>  
 # for a discussion of each configuration directive.  
 # Do NOT simply read the instructions in here without understanding  
 # what they do. They're here only as hints or reminders. If you are unsure  
 # consult the online docs. You have been warned.  
 # Configuration and logfile names: If the filenames you specify for many  
 # of the server's control files begin with "/" (or "drive:/" for Win32), the  
 # server will use that explicit path. If the filenames do *not* begin  
 # with "/", the value of ServerRoot is prepended -- so "logs/foo_log"  
 # with ServerRoot set to "/opt/jboss/httpd/httpd" will be interpreted by the  
 # server as "/opt/jboss/httpd/httpd/logs/foo_log".  
 # ServerRoot: The top of the directory tree under which the server's  
 # configuration, error, and log files are kept.  
 # Do not add a slash at the end of the directory path. If you point  
 # ServerRoot at a non-local disk, be sure to point the LockFile directive  
 # at a local disk. If you wish to share the same ServerRoot for multiple  
 # httpd daemons, you will need to change at least LockFile and PidFile.  
 ServerRoot "/opt/jboss/httpd/httpd"  
 # Listen: Allows you to bind Apache to specific IP addresses and/or  
 # ports, instead of the default. See also the <VirtualHost>  
 # directive.  
 # Change this to Listen on specific IP addresses as shown below to  
 # prevent Apache from glomming onto all bound IP addresses.  
 #Listen 80  
 # Dynamic Shared Object (DSO) Support  
 # To be able to use the functionality of a module which was built as a DSO you  
 # have to place corresponding `LoadModule' lines at this location so the  
 # directives contained in it are actually available _before_ they are used.  
 # Statically compiled modules (those listed by `httpd -l') do not need  
 # to be loaded here.  
 # Example:  
 # LoadModule foo_module modules/  
 LoadModule authn_file_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule authn_dbm_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule authn_anon_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule authn_dbd_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule authn_default_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule authn_alias_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule authz_host_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule authz_groupfile_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule authz_user_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule authz_dbm_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule authz_owner_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule authz_default_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule auth_basic_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule auth_digest_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule advertise_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule file_cache_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule cache_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule disk_cache_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule mem_cache_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule dbd_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule dumpio_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule reqtimeout_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule ext_filter_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule include_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule filter_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule substitute_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule deflate_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule log_config_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule log_forensic_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule logio_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule env_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule mime_magic_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule cern_meta_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule expires_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule headers_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule ident_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule usertrack_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule unique_id_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule setenvif_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule version_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule proxy_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule proxy_connect_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule proxy_ftp_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule proxy_http_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule proxy_scgi_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule proxy_ajp_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule proxy_cluster_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule ssl_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule mime_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule dav_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule status_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule autoindex_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule asis_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule info_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule suexec_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule cgi_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule cgid_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule jk_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule manager_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule slotmem_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule dav_fs_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule vhost_alias_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule negotiation_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule dir_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule imagemap_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule actions_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule speling_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule userdir_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule alias_module /opt/jboss/httpd/lib/httpd/modules/  
 LoadModule rewrite_module /opt/jboss/httpd/lib/httpd/modules/  
 <IfModule !mpm_netware_module>  
 <IfModule !mpm_winnt_module>  
 # If you wish httpd to run as a different user or group, you must run  
 # httpd as root initially and it will switch.  
 # User/Group: The name (or #number) of the user/group to run httpd as.  
 # It is usually good practice to create a dedicated user and group for  
 # running httpd, as with most system services.  
 User daemon  
 Group daemon  
 # 'Main' server configuration  
 # The directives in this section set up the values used by the 'main'  
 # server, which responds to any requests that aren't handled by a  
 # <VirtualHost> definition. These values also provide defaults for  
 # any <VirtualHost> containers you may define later in the file.  
 # All of these directives may appear inside <VirtualHost> containers,  
 # in which case these default settings will be overridden for the  
 # virtual host being defined.  
 # ServerAdmin: Your address, where problems with the server should be  
 # e-mailed. This address appears on some server-generated pages, such  
 # as error documents. e.g.  
 # ServerName gives the name and port that the server uses to identify itself.  
 # This can often be determined automatically, but we recommend you specify  
 # it explicitly to prevent problems during startup.  
 # If your host doesn't have a registered DNS name, enter its IP address here.  
 # DocumentRoot: The directory out of which you will serve your  
 # documents. By default, all requests are taken from this directory, but  
 # symbolic links and aliases may be used to point to other locations.  
 DocumentRoot "/opt/jboss/httpd/htdocs/htdocs"  
 # Each directory to which Apache has access can be configured with respect  
 # to which services and features are allowed and/or disabled in that  
 # directory (and its subdirectories).  
 # First, we configure the "default" to be a very restrictive set of  
 # features.  
 <Directory />  
   Options FollowSymLinks  
   AllowOverride None  
   Order deny,allow  
   Deny from all  
 # Note that from this point forward you must specifically allow  
 # particular features to be enabled - so if something's not working as  
 # you might expect, make sure that you have specifically enabled it  
 # below.  
 # This should be changed to whatever you set DocumentRoot to.  
 <Directory "/opt/jboss/httpd/htdocs/htdocs">  
   # Possible values for the Options directive are "None", "All",  
   # or any combination of:  
   #  Indexes Includes FollowSymLinks SymLinksifOwnerMatch ExecCGI MultiViews  
   # Note that "MultiViews" must be named *explicitly* --- "Options All"  
   # doesn't give it to you.  
   # The Options directive is both complicated and important. Please see  
   # for more information.  
   Options Indexes FollowSymLinks  
   # AllowOverride controls what directives may be placed in .htaccess files.  
   # It can be "All", "None", or any combination of the keywords:  
   #  Options FileInfo AuthConfig Limit  
   AllowOverride None  
   # Controls who can get stuff from this server.  
   Order allow,deny  
   Allow from all  
 # DirectoryIndex: sets the file that Apache will serve if a directory  
 # is requested.  
 <IfModule dir_module>  
   DirectoryIndex index.html  
 # The following lines prevent .htaccess and .htpasswd files from being  
 # viewed by Web clients.  
 <FilesMatch "^\.ht">  
   Order allow,deny  
   Deny from all  
   Satisfy All  
 # ErrorLog: The location of the error log file.  
 # If you do not specify an ErrorLog directive within a <VirtualHost>  
 # container, error messages relating to that virtual host will be  
 # logged here. If you *do* define an error logfile for a <VirtualHost>  
 # container, that host's errors will be logged there and not here.  
 ErrorLog "logs/error_log"  
 # LogLevel: Control the number of messages logged to the error_log.  
 # Possible values include: debug, info, notice, warn, error, crit,  
 # alert, emerg.  
 LogLevel warn  
 <IfModule log_config_module>  
   # The following directives define some format nicknames for use with  
   # a CustomLog directive (see below).  
   LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" combined  
   LogFormat "%h %l %u %t \"%r\" %>s %b" common  
   <IfModule logio_module>  
    # You need to enable mod_logio.c to use %I and %O  
    LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\" %I %O" combinedio  
   # The location and format of the access logfile (Common Logfile Format).  
   # If you do not define any access logfiles within a <VirtualHost>  
   # container, they will be logged here. Contrariwise, if you *do*  
   # define per-<VirtualHost> access logfiles, transactions will be  
   # logged therein and *not* in this file.  
   CustomLog "logs/access_log" common  
   # If you prefer a logfile with access, agent, and referer information  
   # (Combined Logfile Format) you can use the following directive.  
   #CustomLog "logs/access_log" combined  
 <IfModule alias_module>  
   # Redirect: Allows you to tell clients about documents that used to  
   # exist in your server's namespace, but do not anymore. The client  
   # will make a new request for the document at its new location.  
   # Example:  
   # Redirect permanent /foo  
   # Alias: Maps web paths into filesystem paths and is used to  
   # access content that does not live under the DocumentRoot.  
   # Example:  
   # Alias /webpath /full/filesystem/path  
   # If you include a trailing / on /webpath then the server will  
   # require it to be present in the URL. You will also likely  
   # need to provide a <Directory> section to allow access to  
   # the filesystem path.  
   # ScriptAlias: This controls which directories contain server scripts.  
   # ScriptAliases are essentially the same as Aliases, except that  
   # documents in the target directory are treated as applications and  
   # run by the server when requested rather than as documents sent to the  
   # client. The same rules about trailing "/" apply to ScriptAlias  
   # directives as to Alias.  
   ScriptAlias /cgi-bin/ "/opt/jboss/httpd/htdocs/cgi-bin/"  
 <IfModule cgid_module>  
   # ScriptSock: On threaded servers, designate the path to the UNIX  
   # socket used to communicate with the CGI daemon of mod_cgid.  
   #Scriptsock logs/cgisock  
 # "/opt/jboss/httpd/htdocs/cgi-bin" should be changed to whatever your ScriptAliased  
 # CGI directory exists, if you have that configured.  
 <Directory "/opt/jboss/httpd/htdocs/cgi-bin">  
   AllowOverride None  
   Options None  
   Order allow,deny  
   Allow from all  
 # DefaultType: the default MIME type the server will use for a document  
 # if it cannot otherwise determine one, such as from filename extensions.  
 # If your server contains mostly text or HTML documents, "text/plain" is  
 # a good value. If most of your content is binary, such as applications  
 # or images, you may want to use "application/octet-stream" instead to  
 # keep browsers from trying to display binary files as though they are  
 # text.  
 DefaultType text/plain  
 <IfModule mime_module>  
   # TypesConfig points to the file containing the list of mappings from  
   # filename extension to MIME-type.  
   TypesConfig conf/mime.types  
   # AddType allows you to add to or override the MIME configuration  
   # file specified in TypesConfig for specific file types.  
   #AddType application/x-gzip .tgz  
   # AddEncoding allows you to have certain browsers uncompress  
   # information on the fly. Note: Not all browsers support this.  
   #AddEncoding x-compress .Z  
   #AddEncoding x-gzip .gz .tgz  
   # If the AddEncoding directives above are commented-out, then you  
   # probably should define those extensions to indicate media types:  
   AddType application/x-compress .Z  
   AddType application/x-gzip .gz .tgz  
   # AddHandler allows you to map certain file extensions to "handlers":  
   # actions unrelated to filetype. These can be either built into the server  
   # or added with the Action directive (see below)  
   # To use CGI scripts outside of ScriptAliased directories:  
   # (You will also need to add "ExecCGI" to the "Options" directive.)  
   #AddHandler cgi-script .cgi  
   # For type maps (negotiated resources):  
   #AddHandler type-map var  
   # Filters allow you to process content before it is sent to the client.  
   # To parse .shtml files for server-side includes (SSI):  
   # (You will also need to add "Includes" to the "Options" directive.)  
   #AddType text/html .shtml  
   #AddOutputFilter INCLUDES .shtml  
 # The mod_mime_magic module allows the server to use various hints from the  
 # contents of the file itself to determine its type. The MIMEMagicFile  
 # directive tells the module where the hint definitions are located.  
 #MIMEMagicFile conf/magic  
 # Customizable error responses come in three flavors:  
 # 1) plain text 2) local redirects 3) external redirects  
 # Some examples:  
 #ErrorDocument 500 "The server made a boo boo."  
 #ErrorDocument 404 /missing.html  
 #ErrorDocument 404 "/cgi-bin/"  
 #ErrorDocument 402  
 # MaxRanges: Maximum number of Ranges in a request before  
 # returning the entire resource, or 0 for unlimited  
 # Default setting is to accept 200 Ranges  
 #MaxRanges 0  
 # EnableMMAP and EnableSendfile: On systems that support it,  
 # memory-mapping or the sendfile syscall is used to deliver  
 # files. This usually improves server performance, but must  
 # be turned off when serving from networked-mounted  
 # filesystems or if support for these functions is otherwise  
 # broken on your system.  
 #EnableMMAP off  
 #EnableSendfile off  
 # Supplemental configuration  
 # The configuration files in the conf/extra/ directory can be  
 # included to add extra features or to modify the default configuration of  
 # the server, or you may simply copy their contents here and change as  
 # necessary.  
 # Server-pool management (MPM specific)  
 #Include conf/extra/httpd-mpm.conf  
 # Multi-language error messages  
 #Include conf/extra/httpd-multilang-errordoc.conf  
 # Fancy directory listings  
 #Include conf/extra/httpd-autoindex.conf  
 # Language settings  
 #Include conf/extra/httpd-languages.conf  
 # User home directories  
 #Include conf/extra/httpd-userdir.conf  
 # Real-time info on requests and configuration  
 #Include conf/extra/httpd-info.conf  
 # Virtual hosts  
 #Include conf/extra/httpd-vhosts.conf  
 # Local access to the Apache HTTP Server Manual  
 #Include conf/extra/httpd-manual.conf  
 # Distributed authoring and versioning (WebDAV)  
 #Include conf/extra/httpd-dav.conf  
 # Various default settings  
 #Include conf/extra/httpd-default.conf  
 # Secure (SSL/TLS) connections  
 #Include conf/extra/httpd-ssl.conf  
 # Note: The following must must be present to support  
 #    starting without SSL on platforms with no /dev/random equivalent  
 #    but a statically compiled-in mod_ssl.  
 <IfModule ssl_module>  
 SSLRandomSeed startup builtin  
 SSLRandomSeed connect builtin  
 # This Listen port is for the mod_cluster-manager, where you can see the status of mod_cluster.  
 # Port 10001 is not a reserved port, so this prevents problems with SELinux.  
 # This directive only applies to Red Hat Enterprise Linux. It prevents the temmporary  
 # files from being written to /etc/httpd/logs/ which is not an appropriate location.  
 MemManagerFile /var/cache/httpd  
  <Directory />  
   Order deny,allow  
   Deny from all  
   Allow from 192.168.10.  
  # This directive allows you to view mod_cluster status at URL  
  <Location /mod_cluster-manager>  
   SetHandler mod_cluster-manager  
   Order deny,allow  
   Deny from all  
   Allow from 192.168.10.  
  KeepAliveTimeout 60  
  MaxKeepAliveRequests 0  
  ManagerBalancerName other-server-group  
  AdvertiseFrequency 5  
  ServerAdvertise On  
The main areas of concern is:
Somewhere early in the file and:
 # This Listen port is for the mod_cluster-manager, where you can see the status of mod_cluster.  
 # Port 10001 is not a reserved port, so this prevents problems with SELinux.  
 # This directive only applies to Red Hat Enterprise Linux. It prevents the temmporary  
 # files from being written to /etc/httpd/logs/ which is not an appropriate location.  
 MemManagerFile /var/cache/httpd  
  <Directory />  
   Order deny,allow  
   Deny from all  
   Allow from 192.168.10.  
  # This directive allows you to view mod_cluster status at URL  
  <Location /mod_cluster-manager>  
   SetHandler mod_cluster-manager  
   Order deny,allow  
   Deny from all  
   Allow from 192.168.10.  
  KeepAliveTimeout 60  
  MaxKeepAliveRequests 0  
  ManagerBalancerName other-server-group  
  AdvertiseFrequency 5  
  ServerAdvertise On  
Right at the end of the file.

Start up Mod_Cluster

 sudo ./apachectl start  

To Shut down Mod_Cluster

 sudo ./apachectl stop  

You can check that the Mod_Cluster is running by accessing:
 http://<Your IP Address>  
You should get a page that looks like this:
You can also use this url:
 http://<Your IP Address>:10001  
The result should be the same as above.

To check that Mod_Cluster is connecting to you 2 server instances:
 http://<Your IP Address>:10001/mod_cluster-manager  

If your page looks like this then Mod_Cluster is running but Communication between your Cluster group other-server-group and Mod_Cluster is not working correctly or the Servers might be down:


To test the Cluster, access the the web application via the Mod_Cluster:
 http://<Your IP Address>:10001/cluster-demo/  
 http://<Your IP Address>/cluster-demo/  

Mod_Cluster will route requests based on server availability. You can determine which server instance is serving the requests by checking the server console.

Now try shutting down one server instance. Check that the requests are still being processed by the other server.

If all is working then, you have Clustering working!!!


This exercise is merely meant to identify the concepts and principles. You can easily migrate this structure to multiple machines and even add more "slave" instances or nodes.

As always, I would love to hear any feedback, comments or questions. I can also provide technical advise to your organisation if required.

AS7 Cluster Howto
Coder36 - Setting up a JBoss 7.1 Cluster