RED HAT CLUSTER SUITE .
Jul 15, 2015
RED HAT CLUSTER SUITE
.
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.