This Apache High Availability Cluster tutorial is divided into Four Parts series to get the proper and complete understanding about each topic. Before you start reading I would like to clarify that, this guide is addressing both beginners and advance level Linux Administrators.

We will be covering the following topics in this series:

  • Part 1: Basic Concepts of High Availability Cluster
  • Part 2: Apache High Availability LAB Initial Setup & Configuration
  • Part 3: iSCSI Storage Server & Initiator Configuration
  • Part 4: Configure Apache & Cluster Resources for High Availability
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    Part 1: Basic Concepts of High Availability Cluster

    What is High Availability?

    The term High Availability” most commonly used in information technology world which means an IT system with a high level of availability. The system which is continuously operational and available for the delivery of services or resources it provides for end users.

    • In more simple words it is a system design approach and implementation of different services in a way, that achieve highest level of performance and availability of system infrastructure by eliminating a single point of failure.

    What is High Availability Cluster?

    A High Availability Cluster is a group of multiple computers act as a single system and provides continues uptime when a certain service or even whole computer from the group fails.

    A failover cluster is not just start and stop services in case of failure, it has layers of components associated with it. The following diagram represents different layers of cluster stack software.

    Apache High Availability Cluster
    Cluster Stack in RHEL7 / CentOS 7

    What is Pacemaker?

    Pacemaker is an open source high availability cluster software for Linux operating system which is also known as “Cluster Resource Manager”.

    • RHEL 7/CentOS 7 provides failover clustering functionality using pacemaker.

    The Cluster Resource Management Layer provides following features:

    • Start and Stop cluster Resources
    • Monitoring cluster Resources
    • Migrating cluster Resources
    • Grouping cluster resources
    • Location Checks

    What is Corosync?

    Corosync is a group of cluster communication system provides all the cluster communication features and capabilities. Pacemaker (Cluster Resource Manager) uses Corosync for internal cluster stack communication, Corosync also provides Quorum System.

    • Quorum System is the minimum number of votes from cluster members which is require to perform a cluster operation such as transferring resources from failed node to working available node.

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