The cluster communication layer is the bottom layer of the cluster software stack and provides continuous communication between all the computer cluster nodes. Continuous communication between the cluster members is required for normal cluster operation. It is a priority for cluster members to get all of the information required about the current computer cluster configuration and status at any time. The cluster members must always know the exact number of the cluster nodes currently forming the computer cluster, and must also be notified immediately if a cluster member joins or leaves the computer cluster. Successful cluster communication can be achieved only when all the cluster members are connected to each other and able to communicate. This is why you must carefully decide the sort of cluster connection the members will use to communicate to each other. The types of supported cluster connection are defined by the cluster communication software. The most...

The cluster resource management layer is the top layer of the cluster stack. It makes sure that the services your cluster provides are up-and-running at all times.

The features of the cluster resource management layer are as follows:

The main objective of the cluster resource management layer is to relocate cluster resources and services to operational cluster members when there is a failure in the cluster. In order for the cluster resource management layer to manage cluster services, it must be able to access the applications providing the cluster service. The services and applications the cluster resource manager provides are called cluster resources. These resources can be anything such as an IP address, web server, database server, or any other application available on the operating system. The cluster...

In order to make it easy for you to understand the cluster service, you will be presented with a theoretical example of a two-node active/passive computer cluster providing a website cluster service. The active/passive cluster configuration only provides operational cluster services on the master cluster member at a given time, while the secondary cluster member waits on standby to take over if there is a master node failure. If the currently active cluster member fails, the cluster resources will be relocated and recovered on the operational secondary cluster member.

The following resources are required to run a simple website:

All the listed resources must be installed and configured on the cluster node operating system and also added to the cluster resource manager configuration. In this way, the cluster resource manager is able to manage the resources and provide failover capabilities...

There are endless possibilities and platforms a computer cluster can be installed and configured on and, therefore, also different software building the cluster stack. Since the objectives of this book are to familiarize you with the high-availability cluster running on CentOS Linux, I will present you with the cluster stack software to be used to install and configure a highly available computer cluster on CentOS Linux.

CentOS is a Community Enterprise Operating System. It is a Linux distribution that provides a free enterprise platform. The functionalities of CentOS are compatible with its commercial upstream source: Red Hat Enterprise Linux (RHEL). The current major CentOS version is 7 and was released on July 7, 2014. It offers many changes compared to its predecessor, CentOS version 6. Probably due to this and the fact that CentOS 6 maintenance updates will be supported until November 30, 2020, the majority of CentOS Linux servers still run CentOS version...

The first step towards building your highly available computer cluster is the operating system installation. We will not cover the details of installing CentOS Linux on the server machines. I can only mention that it is always good practice to install the minimum number of packages required. This is the beauty of using the Linux operating system in general, and also CentOS Linux specifically. CentOS has an option for minimal installation, which actually installs only the basic required packages for normal functioning of the operating system. This is an advantage because the more packages are used, the higher the possibility that one of the packages will go berserk and cause trouble at the operating system level. It is also an advantage for patching the systems, since there are fewer packages to patch.

All the dependencies and required packages will be installed while installing the cluster stack software of your choice. Note that you can...

In this chapter, you became familiar with cluster stacks and cluster stack layers. Each cluster stack layer was explained in detail by elaborating on the tasks it must provide and how to provide them. You also learned about the cluster software stack solutions that will be presented in practical examples in the following chapters of this book, and the necessary preparations and recommendations before installing the cluster software stack. In the next chapter, you will prepare the operating system to run the cluster stack software. You will follow step-by-step instructions on how to install and configure operating system requirements and cluster communication software.