WildFly Cluster on Raspberry Pi (Tech Tip #28)

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Tech Tip #25 showed how to configure WildFly on Raspberry Pi. Tech Tip #27 showed how to setup WildFly on two Raspberry Pis in managed domain mode. This tech tip will show how to setup a WildFly cluster over those two hosts.

WildFly supports mod_cluster out of the box. There are several advantages of mod_cluster:

  • Dynamic configuration of httpd workers
  • Server-side load balance factor calculation
  • Fine-grained web app lifecycle control

However there is no ARM build available for it, yet. So we’ll use mod_proxy instead that gets pre-installed as part of Apache2. The Domain Controller and HTTP server need not be on the same host and that’s the configuration we’ll use for our setup. So effectively, there will be three Raspberry Pis:

  • Domain Controller
  • Host Controller
  • Web Server

raspi-cluster-techtip28

Lets get started!

  1. Before installing any modules, including Apache, on Raspbian, the system needs to be fully updated:
    Trying to install Apache without updating the system will give weird errors:
    Now install Apache HTTP as:
    The log messages show that server’s name could not be determined, and 127.0.1.1 is instead used for ServerName. This can be fixed by editing “/etc/apache2/apache2.conf” and adding the following line:
  2. After Apache is installed, “mod_proxy” modules already exists in the “/usr/lib/apache2/modules” directory, and just need to enabled.Create “/etc/apache2/mods-enabled/mod_proxy.load” as:
    This file will be picked up via a direcinve in “/etc/apache2/apache2.conf”.

    Restart the server:

    If there are any errors, then you can see them in “/var/log/apache2/error.log” directory.

    The list of modules loaded can be seen using:

    The newly loaded modules are highlighted in bold.

  3. Provide convenient host names for each of the Raspberry Pis. The names chosen for each host is shown in the table below:
    IP Address Role Host Name
    10.0.0.27 Domain Controller raspi-master
    10.0.0.28 Host Controller raspi-slave
    10.0.0.29 Web Server raspi-apache

    This is enabled by editing “/etc/hostname” on each Raspberry Pi and changing “raspberrypi” to the given name.

    In addition, “/etc/hosts” on each Raspberry Pi need to make two entries of the following format:

    Here <IP Address> and <Host Name> for each host needs to be used from the table above.

    Finally, added the following entries on “/etc/hosts” on my local Mac:

    This ensures that any cookies are set from the same domain.

    Flush the DNS using:

    Now raspi-master.example.com:8330 in the browser shows:

    raspi-master-defaultoutput-techtip28

    And similarly raspi-slave.example.com:8330 shows:

    raspi-slave-default-output-techtip28

  4. Configure mod_proxy load balancer by editing “/etc/apache2/apache2.conf” and add the following lines at the end of the file:

    This directive provide load balancing between “master” and “slave”. “Header” and “ProxySet” directive provides sticky session.

Now accessing raspi-apache.example.com/http-1.0-SNAPSHOT/index.jsp shows:

raspi-apache-default-output-techtip28

And so in three parts (part 1 and part 2), we learned how to setup a WildFly cluster on Raspberry Pi!

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Related posts:
  1. WildFly on Raspberry Pi (Tech Tip #25)
  2. WildFly Managed Domain on Raspberry Pi (Tech Tip #27)
  3. Compiling Apache HTTPD on Mac (Tech Tip #45)
  4. WildFly 9: Features and Getting Started (Tech Tip #43)
  5. Load Balance WebSockets using Apache HTTPD (Tech Tip #48)

3 thoughts on “WildFly Cluster on Raspberry Pi (Tech Tip #28)”

  1. Thanks for the tutorial.

    When you have a server running the same static addres all the time you should change the address 127.0.1.1 in /etc/hosts to your machines proper IPv4 address.

    To change the name of the machine you change raspberrypi in /etc/hosts and /etc/hostname and maybe in /etc/mailname to the new name.

    To enable (and disable) sites and modules in apache2 you can/should use a2ensite and a2disite resp a2ensmod and a2dismod. See man pages.

    To set up sites, you copy /etc/apache2/sites-available/000-default.conf to /etc/apache2/sites-available/name.conf and edit it and run a2ensite name.

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  3. Hello there, You have done a fantastic job. I will certainly digg it and
    personally suggest to my friends. I’m sure they’ll be benefited from this site.

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