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Configuring Cluster Fencing Agents in a Pacemaker Cluster

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Creating a fence device A system administrator can create a fence device in the cluster with the pcs stonith create command: # pcs stonith create name fencing_agent parameters The command requires additional arguments, such as the fencing agent and the fencing parameters required for the fencing agent. There are generic properties for all the fencing agents shipped with Red Hat Enterprise Linux High Availability Add-on: stonith-timeout This setting defines the time to wait for fencing … [Read more...] about Configuring Cluster Fencing Agents in a Pacemaker Cluster

Setting Up Fencing Devices in a Pacemaker Cluster

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Overview of fence device configuration Fencing is a requirement for every operational cluster. The first step when setting up fencing for the cluster is the setup of the hardware or software device that does the actual fencing. The Red Hat Enterprise Linux High Availability Add-on provides a variety of fencing agents for use with different fence devices. The pcs stonith list provides a list of all installed fencing agents: # pcs stonith list fence_apc - Fence agent for APC over … [Read more...] about Setting Up Fencing Devices in a Pacemaker Cluster

What is fencing and What are different methods of fencing in a pacemaker cluster

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What is fencing? The Red Hat High Availability Add-on uses fencing to ensure data integrity in the cluster. Fencing is often accomplished by powering the node off since a dead node is clearly not able to do anything. In other cases, a combination of operations will be used to cut the node off from the network (to stop new work from arriving) or from storage (to stop the node from writing to shared storage). Fencing is a necessary step in service and resource recovery in a cluster. The Red Hat … [Read more...] about What is fencing and What are different methods of fencing in a pacemaker cluster

Managing Quorum Calculations in a Pacemaker Cluster

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Set quorum calculation options The votequorum component allows a cluster administrator to build clusters with switches that alter the way quorum gets calculated. When building a new cluster with the pcs cluster setup command, the following switches may be added to change the behavior of quorum handling in the cluster: --wait_for_all Wait for all cluster members to be online before starting to calculate quorum. This setting effectively prevents a fence race when the cluster is starting up. … [Read more...] about Managing Quorum Calculations in a Pacemaker Cluster

What is quorum in a pacemaker cluster (Understanding Quorum Operations)

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What is quorum? In order for a cluster to work as expected, the nodes must be in agreement on certain facts, such as which machines are currently cluster members, where services are running, and which machines are using which resources. The method in which this is implemented in the Red Hat High Availability Add-on is by the use of a majority voting scheme. Every cluster node casts one vote if it successfully joins the corosync network communication and is able to communicate with the other … [Read more...] about What is quorum in a pacemaker cluster (Understanding Quorum Operations)

Prohibiting a cluster node from hosting resources in pacemaker cluster (putting a node into standby mode)

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There are times when an administrator needs to temporarily suspend resource hosting of a cluster node without disrupting regular cluster operation. This can happen, for example, when a critical security update needs to be applied for the hosted resource. The update can be applied after putting node by node into standby mode, resulting in reduced downtime. A different use case is to test resource migration. When a node is put in standby mode, it does not get any resources assigned. Resources that … [Read more...] about Prohibiting a cluster node from hosting resources in pacemaker cluster (putting a node into standby mode)

Managing Cluster Membership in pacemaker cluster (Adding and removing a cluster node)

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The Red Hat High Availability Add-on provides different ways for a system administrator to control membership of cluster nodes: Starting and stopping the cluster services control whether a cluster node is participating in the cluster at runtime. Enabling and disabling the cluster services control whether a cluster node automatically starts the cluster services and joins the cluster when it boots. Adding and removing a cluster node from the cluster permanently changes whether the node is a … [Read more...] about Managing Cluster Membership in pacemaker cluster (Adding and removing a cluster node)

How to Configure CentOS/RHEL 5,6 to use /etc/passwd to Store Passwords Instead of /etc/shadow

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The Ask: CentOS/RHEL 5,6 systems needs to be configured to use /etc/passwd to store passwords instead of using /etc/shadow. DISCLAIMER: It is not recommended or advise customers to move from /etc/shadow due to potential security risks. So use this method with caution. The steps for making authentication work without /etc/shadow are as follows: 1. Boot into single user mode. 2. Edit /etc/sysconfig/authconfig changing: USESHADOW=yes Change to: USESHADOW=no 3. If this directive is … [Read more...] about How to Configure CentOS/RHEL 5,6 to use /etc/passwd to Store Passwords Instead of /etc/shadow

Beginner Guide to RHEL 7 high-availability cluster – Architectural Overview

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What is a cluster? A cluster is a set of computers working together on a single task. Which task is performed, and how that task is performed, differs from cluster to cluster. There are two different kinds of clusters covered in this post and upcoming posts to come in this series. 1. High-availability clusters: The goal of a high-availability cluster, also known as an HA cluster or failover cluster, is to keep running services as available as they can be. This is primarily achieved by having … [Read more...] about Beginner Guide to RHEL 7 high-availability cluster – Architectural Overview