Book Image

CentOS High Performance

By : Gabriel Cánepa
Book Image

CentOS High Performance

By: Gabriel Cánepa

Overview of this book

CentOS is the enterprise level Linux OS, which is 100% binary compatible to Red Hat Enterprise Linux (RHEL). It acts as a free alternative to RedHat's commercial Linux offering, with only a change in the branding. A high performance cluster consists in a group of computers that work together as one set parallel, hence minimizing or eliminating the downtime of critical services and enhancing the performance of the application. Starting with the basic principles of clustering, you will learn the necessary steps to install a cluster with two CentOS 7 servers. We will then set up and configure the basic required network infrastructure and clustering services. Further, you will learn how to take a proactive approach to the split-brain issue by configuring the failover and fencing of the cluster as a whole and the quorum of each node individually. Further, we will be setting up HAC and HPC clusters as a web server and a database server. You will also master the art of monitoring performance and availability, identifying bottlenecks, and exploring troubleshooting techniques. At the end of the book, you’ll review performance-tuning techniques for the recently installed cluster, test performance using a payload simulation, and learn the necessary skills to ensure that the systems, and the corresponding resources and services, are being utilized to their best capacity.
Table of Contents (13 chapters)
CentOS High Performance
About the Author
About the Reviewers

Quorum – scoring inside your cluster

In simple terms, the concept of quorum indicates the minimum number of members that are required to be active in order for the cluster, as a whole, to be available. Specifically, a cluster is said to have quorum when the number of active nodes is greater than the total number of nodes divided by two. Another way to express this is that quorum is achieved by at least a simple majority (50% of the total number of nodes + 1).

Although the concept of quorum doesn't prevent a split-brain scenario, it will decide which node (or group of nodes) is dominant and allowed to run the cluster so that when a split-brain situation occurs, only one node (or group of nodes) will be able to run the cluster services.

By default, when the cluster does not have quorum, pacemaker will stop all resources altogether so that they will not be started on more nodes than desired. However, a cluster member will still listen for other nodes to reappear on the network, but they will...