RED HAT CLUSTER SUITE

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RED HAT CLUSTER SUITE OVERVIEW

What is Red Hat Cluster Suite

• Red Hat server is a suite of packages that can be used to deploy highly available services on Red Hat Linux-based servers

• Provides three main features:

• – Cluster management and service failover

• – Network load-balancing (LVS)

• – Global read-write file system (GFS) (HPC)

What is required to run a cluster?

• Two or more Servers either physical or Virtual.

• Two or more bonded NICs to send cluster heartbeat messages over (this is optional, but highly recommended!)

• Two or more bonded NICs dedicated to public network traffic

• Supported fencing solution

• Shared storage

What does a cluster consist of?

An HA cluster typically consists of the following items:

• Two or more nodes

• One or more fence devices

• Shared storage

• Public and private network interfaces

• One or more resources

• One or more services

• Quorum devices

• Failover Domains

Quorum devices

• Quorum is used to ensure that a majority of nodes areavailable in the cluster

• Needed to avoid split-brain conditions

• Works by assigning one or more votes to each server andquorum device in the cluster

• To ensure quorum, a cluster needs to have 51% of theavailable votes to form or continue running anoperational cluster

Fencing devices • Fencing devices provide a way for the cluster to remove

an unresponsive node from the cluster

• Nodes are typically fenced when they are unresponsive, and fencing is done to prevent split brain configurations

• Several supported ways to fence nodes:

• – IPMI (Intelligent Platform Management Interface)• – Power Fencing

• – SAN fencing

• – VMware virtual centre fencing, RHEVM, KVM fencing etc.

• – Vendor specific methods

• – HP –ILO (Integrated Lights Out)

• – Dell – DRAC ( Dell Remote Access Control)

• – IBM Blade Centres

Cluster resources

• Cluster resources provide the basic unit of configuration in a cluster

• Several types of resources exist by default: • – Apache

• – GFS

• – MYSQL

• – Oracle

• – Samba

• – NFS

• – Tomcat

• – IP Address

• – Start/Stop Scripts

• – Services

Cluster Services/ Resource Group

• Services are collections of resources that serve a specific purpose

• An example of this would be an HA APACHE service that contains three resources:

• – An IP address resource that is tied to the APACHE webpage database instance

• – File system resources that contain the web page ex: /var/www/html

• – httpd services that starts, stops and verifies that http is running (script: /etc/init.d/httpd)

Failover domains

• Failover domains allow you to define where servicesshould go when a service faults and is migrated toanother node

• Each failover domain can have a unique list of nodes, andeach node can be assigned a priority to tell the cluster itis a better candidate to run the service

Red Hat Cluster Components

• Luci

• Ricci

• Conga

• CMAN (Cluster Manager)

• RGManager (Resource Group Manager)

• CLVM ( Clustered LVM)

• GFS (Global File System)

CLVM –OVERVIEW

CLVM – Clustered LVMClvm:• Provides volume management of cluster storage.• A cluster-wide version of LVM2• CLVM provides the same capabilities as LVM2 on a single node, but

makes the logical volumes created with CLVM available to all nodesin a cluster.

• CLVM uses the lock-management service provided by the clusterinfrastructure.

• Using CLVM requires minor changes to /etc/lvm/lvm.conf for clusterwide locking.

clvmd:• – A daemon that provides clustering extensions to the standard

LVM2 tool• set and allows LVM2 commands to manage shared storage.• – Runs on each cluster node.• – Distributes LVM metadata updates in a cluster, thereby presenting

each cluster node with the same view of the logical volumes

GFS – Global File system OverviewPictorial Representation of GFS cluster

GFS- Global File System• The Red Hat GFS file system is a native file system that interfaces

directly with the Linux kernel file system interface (VFS layer). A GFS filesystem can be implemented in a standalone system or as part of acluster configuration. When implemented as a cluster file system, GFSemploys distributed metadata and multiple journals.

• A GFS file system can be created on an LVM logical volume. A logicalvolume is an aggregation of underlying block devices that appears as asingle logical device

• GFS is based on a 64-bit architecture, which can theoreticallyaccommodate an 8 EB file system. However, the current supportedmaximum size of a GFS file system is 25 TB.

• GFS supports up to 125 GFS nodes.