Linux Cluster Concepts

Linux Cluster
Administration RHEL 5
1Linux Clustering Document www.expertslogin.com

Linux Cluster Concepts And
Administration on RHEL 5
Cluster Basics
What is cluster
Cluster types
Storage
High Availability
Load balancing
High performance

Storage Clusters
Provide consistent file system image across
nodes
Simplify storage administration
Simplify backup & disaster recovery
RHCS provides storage clustering through
Red Hat GFS

High Availability Clusters
Provide 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 clustering
through its High availability Service
Management component

Load balancing clusters
Dispatch network service requests to multiple
cluster nodes
Provide cost-effective scalability
Failures in a load-balancing cluster are not
visible from outside the cluster
RHCS provides load-balancing through LVS

Performance Clusters
Use cluster nodes to perform concurrent
calculations
Allow applications to work in parallel
Referred to as computational clusters or grid
computing

Red Hat Cluster Suite
RHCS
RHCS major components:
RHCS optional components
Cluster infrastructure
HA Service Management
Cluster Administration tools
Linux Virtual Server ( LVS)
Global File System (GFS)
Cluster Logical Volume Manager (CLVM)
Global Network Block Device (GNBD)

Red Hat Cluster Suite
RHCS

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
Lock 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 fencing
External
Integrated

Cluster Infrastructure Cluster
ConfigurationSystem
(CCS)
CCS manage cluster configuration
CCS provide information to other cluster
components
CCS ensures configuration file is up-to-date
in all nodes

Configuration file /etc/cluster/cluster.conf
Cluster characteristics
Cluster Infrastructure Cluster
ConfigurationSystem
(CCS)
Cluster name
Cluster
Fence Device
Managed Resources

HA Service Management
Create & 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 Domains
Failover characteristics
Unrestricted
Restricted
Unordered
Ordered
Failback

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-
sions
to LVM2

Provides block-device access to GFS over
TCP/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 Block
Device (GNBD)

Set of integrated s/w for load balancing
Runs on equally configured computers
LVS roles:
Linux Virtual Server (LVS)
Active LVS router
Backup LVS router
Load balancing
Integrity of services check

Two tiers : LVS routers & real servers
Active LVS router uses NAT to direct from
public 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 load
balancing algorithms

Load-balancing algorithms:
Round-Robin Scheduling
Weighted Round-Robin Scheduling
Least-Connection
Weighted Least-Connections (default)

NAT Routing
Direct Routing
Routing Methods:

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
Conga
luci
ricci

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

Linux Cluster Concepts

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