Hello everyone.

Today we will learn how we can setup & configure Pacemaker on two CentOS 7 Linux servers for high availability purposes. I will stuck with the very basic fundamental and I will not dive deep on it over here for this tutorial.

Let’s begin then.

First, we need to know what is CentOS, Pacemaker and High Availability and why we need them.

Why CentOS?

CentOS Linux is a community-supported distribution derived from sources freely provided to the public by Red Hat for Red Hat Enterprise Linux (RHEL). As such, CentOS Linux aims to be functionally compatible with RHEL. The CentOS Project mainly changes packages to remove upstream vendor branding and artwork. CentOS Linux is no-cost and free to redistribute. Each CentOS version is maintained for up to 10 years (by means of security updates — the duration of the support interval by Red Hat has varied over time with respect to Sources released). A new CentOS version is released approximately every 2 years and each CentOS version is periodically updated (roughly every 6 months) to support newer hardware. This results in a secure, low-maintenance, reliable, predictable and reproducible Linux environment.

You can download CentOS from here. You can directly download the ISO file format disk image of CentOS 7 from here.

What is Pacemaker?

Pacemaker is an open source high availability resource manager software used on computer clusters since 2004 for achieving high availability of systems. Till 2007, it was a part of the Linux-HA project and then it was split out to be it’s own project. It achieves maximum availability for your cluster services  by detecting and recovering from node and resource-level failures by making use of the messaging and membership capabilities. Pacemaker provides a distributed Cluster Information Base (CIB) in which it records the configuration and the status of all cluster resources among it. The CIB automatically replicates to all cluster nodes from the Designated Coordinator. Designated Coordinator is one node that Pacemaker automatically elects from all available cluster nodes. In Pacemaker, the shell allows us to configure cluster resources. Pacemaker’s Policy Engine (PE) recurrently checks the cluster configuration against the cluster status and initiates actions as required

What is High Availability?

High availability refers to such a system which  is continuously operational for a desirably long period of time without any down time or failure. It eliminates single points of failure with redundancy with a detection of failure. By implementing high availability system, uptime and availability can be make sure for your service. So by having high availability you can easily handle service outage.

Prerequisites

• You must have root user access for all the servers.
• For this tutorial, we will use two (2) CentOS 7 Linux servers where one will be the primary and the another one will be used as backup which in turns will work like a high availability system. These two (2) CentOS 7 Linux servers will form a cluster and these two (2) will be the two nodes for this cluster. You can use 3 or 4 whatever number of nodes that you need to serve your services as per your requirements.
• You need to assign IP address manually or static IP address need to be assign on your NIC / LAN card interface of your server. I am using 192.168.1.12 IP address for the primary and 192.168.1.13 IP address for the backup CentOS 7 Linux server. I am considering that, you know how you can assign IP address manually on your LAN / NIC card interface <img draggable="false" class="emoji td-animation-stack-type0-1" alt="