Redhat Clustering

types of clusters
1.Storage
2.High Availability
3.Load Balancing
4.High Performance

Redhat Cluster Suite (RHCS)
RHCS consists of the following major components
Cluster Infrastructure
High Availability Service Management
Cluster Administration Tools
Linux Virtual Server

Additional components which are used to supplement RHCS but not part of the RHCS are
Red Hat Global File System(GFS)
Cluster Logical Volume Manager(CLVM)
Global Network Block Device(GNBD)

Cluster Infrastructure
Cluster Infrastructure performs the following functions
Cluster Management
Lock Management
Fencing
Cluster Configuration Management

Cluster Management
Cluster Manager(CMAN) manages cluster quorum and cluster membership. CMAN is a distributed cluster manager and runs on each cluster node. If more than half the cluster nodes are active the cluster has quorum.

Lock Management
In RHCS, Distributed Lock Manager(DLM) is the lock manager. GFS and CLVM use locks form the DLM.

Fencing
The cluster infrastructure performs fencing though the fence daemon, fenced. Fenced when notified of a failed cluster node, fences the failed node. The fencing daemon determines from the cluster configuration file which fencing method to use. Two key elements in the cluster configuration file define a fencing method. They are fencing agent and fencing device.

RHCS provides a variety of fencing methods.
Power fencing
Fibre Channel switch fencing
GNDB fencing
Other fencing(e.g.: IBM Bladecenter, PAP, DRAC/MC, HP ILO, IPMI, IBM RSA II)

Cluster Configuration System(CCS)
CCS runs in each cluster node and makes sure that the cluster configuration file in each cluster node is up to date. The cluster configuration file /etc/cluster/cluster.conf is an XML file that describes the following cluster characteristics
1.Cluster Name – contains cluster name, cluster configuration file revision number, basic fence timing properties when a node joins a cluster or is fenced from the cluster.
2.Cluster – Displays each node in the cluster, specifying node name, node ID, number of quorum votes, and fencing method for that node.
3.Fence Device – Displays fence devices in the cluster, along with the details to use them.
4.Managed Resources – Displays resources required to create cluster services.


High availability Service Management
Provides the ability to create and manage highly available cluster services. The key component is “rgmanager” which implements cold failover for off the shelf applications. You can associate a cluster service with a failover domain. Failover domains are not required for operation. A failover domain is a subset of cluster nodes that are eligible to run a particular cluster service. A cluster service can run on only one cluster node at a time to maintain data integrity. One can specify failover priority in a failover domain.

RedHat GFS
GFS is a cluster file system that allows a cluster of nodes to simultaneously access a block device that is shared among the nodes. GFS uses a lock manager to co-ordinate I/O. Volume management is managed through CLVM. GFS provides features such as quotas, multiple journals, and multipath support.

GFS Deployment scenarios are based on performance, scalability, and economy. GFS on a fibre SAN fabric is used for highest performance and scalability, but is quite expensive. One can use GFS and GNBD with a SAN for slightly less costly solution. GFS and GNBD with directly connected storage would be the most economical option.

Cluster Logical Volume Manager
CLVM provides a cluster wide version of LVM2. The key component in CLVM is clvmd. Clvmd runs in each cluster node and distributes lvm metadata updates in a cluster to all the nodes.

Global Network Block Device
GNBD provides block device access to redhat GFS over TCP/IP. GNBD consists of 2 major components: a GNBD client and a GNBD server. A GNBD server runs on a node and exports block level storage from it's local storage. A GNBD client runs in a node with GFS and imports a block device exported by a GNBD server.

Linux Virtual Server.
LVS is a set of software components used for load balancing IP traffic. The LVS router is also responsible for checking the integrity of the service on each real server.

Cluster Administration Tools
Conga – Web based management tool
system-config-cluster – GUI tool for managing a clustering
Command line tools for managing a cluster.
1.ccs_tool
2.ccs_test
3.cman_tool
4.fence_tool
5.fence_node
6.clustat
7.clusvcadm

Thanks to Author, orignal source http://blog.sushilsuresh.co.uk/2008/09/redhat-clustering-overview.html