Linux Cluster Concepts

Linux ClusterAdministration

RHEL 5

1Linux Clustering Document www.expertslogin.com


Linux Cluster Concepts And Administration on RHEL 5

Cluster BasicsWhat is cluster

Cluster typesStorageHigh AvailabilityLoad balancingHigh performance



Storage ClustersProvide consistent file system image across nodes

Simplify storage administration

Simplify backup & disaster recovery

RHCS provides storage clustering through Red Hat GFS



High Availability ClustersProvide continuous availability of services

Maintain data integrity

Node failures in a high-availability cluster are not vis-ible from outside the cluster

RHCS provides high-availability clusteringthrough its High availability ServiceManagement component



Load balancing clustersDispatch network service requests to multiple cluster nodes

Provide cost-effective scalability

Failures in a load-balancing cluster are notvisible from outside the cluster

RHCS provides load-balancing through LVS



Performance ClustersUse cluster nodes to perform concurrentcalculations

Allow applications to work in parallel

Referred to as computational clusters or gridcomputing



Red Hat Cluster SuiteRHCS

RHCS major components:

RHCS optional components

Cluster infrastructureHA Service ManagementCluster Administration toolsLinux Virtual Server ( LVS)

Global File System (GFS)Cluster Logical Volume Manager (CLVM)Global Network Block Device (GNBD)



Red Hat Cluster SuiteRHCS



Cluster Management

Lock Management

Fencing

Cluster Configuration Management

Cluster Infrastructure



Cluster Infrastructure Cluster Management(CMAN)

Distributed across all nodes

CMAN track cluster quorum Prevents split-brain

CMAN tracks membership



Service provides mechanism for other cluster components to synchronize their access to shared resources

Distributed Lock Manager (DLM)

GFS & CLVM use locks from DLM

Cluster Infrastructure Cluster Management(CMAN)

Cluster InfrastructureLock Management



Cluster Infrastructure Fencing

Disconnection of a node from the cluster’s shared storage fenced daemon performs fencing

DLM & GFS recover after fenced

Fencing methods



Fencing methods:

SCSI3 Persistent Reservation Fencing

Fiber Channel switch fencing

GNBD fencing

Cluster Infrastructure Fencing

Power fencingExternalIntegrated



Cluster Infrastructure Cluster ConfigurationSystem (CCS)

CCS manage cluster configuration

CCS provide information to other clustercomponents

CCS ensures configuration file is up-to-datein all nodes



Configuration file /etc/cluster/cluster.conf

Cluster characteristics

Cluster Infrastructure Cluster ConfigurationSystem (CCS)

Cluster nameClusterFence DeviceManaged Resources



HA Service ManagementCreate & manage HA cluster services

rgmanager implements cold failover

HA service must be configured in cluster.conf

Associate service to failover domain

Failover priority in a failover domain



Failover Domains



Failover DomainsFailover characteristics

UnrestrictedRestrictedUnorderedOrderedFailback



GFS/GFS2 is a native file system

GFS/GFS2 provides data sharing among nodes with single, consistent view of the file system name space

GFS/GFS2 file system must be created on an LVM logical volume (linear or mirror)

Red Hat Global File System



Cluster Logical Volume(CLVM)

CLVM provides the same capabilities as LVM2 on a single node

CLVM makes volume available to all nodes

clvmd daemon provides clustering exten-sionsto LVM2



Provides block-device access to GFS overTCP/IP Useful when FC or single initiator SCSI are not necessary or are cost prohibitive

GNBD client , GNBD server

Global Network Block Device (GNBD)



Global Network BlockDevice (GNBD)



Set of integrated s/w for load balancing

Runs on equally configured computers

LVS roles:

Linux Virtual Server (LVS)

Active LVS routerBackup LVS router

Load balancingIntegrity of services check






Two tiers : LVS routers & real servers

Active LVS router uses NAT to direct frompublic network to real servers

Service requests arrive to LVS to a virtual IP (VIP)

Only one LVS is active at a time

LVS distributes requests based on loadbalancing algorithms





Load-balancing algorithms:

Round-Robin SchedulingWeighted Round-Robin SchedulingLeast-ConnectionWeighted Least-Connections (default)

NAT RoutingDirect Routing



Routing Methods:




Cluster Administration tools

Conga

Cluster Administration GUI

Command line administration tools



s/w provides centralized configuration &management

Conga primary components

luci server runs on one computer & commu-nicates with multiple clusters & computers via ricci

ricci agent that runs on each computer

Cluster Administration toolsConga

luciricci



System-config-cluster

Cluster status tool

Cluster Administration GUI

- ccs_tool → cluster configuration- cman_tool → cluster management- fence_tool → fence tool- clustat → cluster status- clusvcadm → cluster user service administration



Command Line Administration Tools

Cluster Administration tools

Linux Cluster Concepts

Technology