Cluster Basis & type of Clusters.
Two or more computers that work together to perform a task is called a cluster.
Example:
Storage Cluster Provides a consistent file system image across servers in a cluster, which allows servers to simultaneously read and write to a single shared file system.
Type of clusters:
Load Balancing cluster to dispatch network service requests to multiple cluster nodes.
Storage cluster to provide consistent file system storage image.
High Performance cluster to perform concurrent calculations for applications.
High Availability or Fail-over clusters provides continuous availability of services.
Example:
Red Hat Cluster is an integrated set of software components. RHCS consists of the following major, components.
Cluster infrastructure - which Provides fundamental functions for nodes to work together as a cluster.
High-availability Service Management — Provides failover of services from one cluster node to another in case a node becomes inoperative.
Cluster administration tools — Configuration and management tools for setting up, configuring, and managing a Red Hat cluster.
Linux Virtual Server (LVS) — Routing software that provides IP-Load-balancing.
Other optional package (and not part of Red Hat Cluster Suite) are as follows:
GFS (Global File System) and GFS2 (Global File System2) allows multiple nodes to share storage at a block level as if the storage were connected locally to each cluster node.
Cluster Logical Volume Manager (CLVM) — Provides volume management of cluster storage.
Cpanel DNS Cluster Configuration - how it should be configured
If at all possible, you should link your web server directly to the DNS servers, you will need to sync each web server to its DNS servers.
Performance:
Creating a cluster setup with direct links between servers can decrease CPU load, improving the performance of your servers. The more steps, or “hops,” between a web server and a nameserver, the slower the servers’ performance will be.
You should not set a DNS server to sync data back to a web server, as this will put extraneous data on the web server.
For each intermediate server you add, the data transfer time is 3 times slower than for a direct link.
Creating Volume Groups in a Cluster
You create volume groups in a cluster environment with the vgcreate command, just as you create them on a single node.
By default, volume groups created with CLVM on shared storage are visible to all computers that have access to the shared storage. It is possible, however, to create volume groups that are local, visible only to one node in the cluster, by using the -c n of the vgcreate command.
The following command, when executed in a cluster environment, creates a volume group that is local to the node from which the command was executed. The command creates a local volume named vg1 that contains physical volumes /dev/sdd1 and /dev/sde1.
vgcreate -c n vg1 /dev/sdd1 /dev/sde1
You can change whether an existing volume group is local or clustered with the -c option of the vgchange command.
You can check whether an existing volume group is a clustered volume group with the vgs command, which displays the c attribute if the volume is clustered.
EXAMPLES
To create a volume group named test_vg using physical volumes /dev/hdk1, and /dev/hdl1 with default physical extent size of 4MB:
vgcreate test_vg /dev/sdk1 /dev/sdl1
