Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.1 Instrukcja Użytkownika Pobierz pdf (Strona 28)

Introduction to Linux Clustering

8.3 Five node HA cluster with DRBD + Xen

The five-node DRBD cluster design above can be extended to become a HA Xen cluster. The

three production nodes can be configured as Xen hosts, with the Xen guests being booted

from the network and using NFS for storage (just like the hosts themselves).

Cluster Suite is running on the host node, and in the event of a Xen VM failing or the entire

host itself suffering a failure, Cluster Suite can start each Xen VM on an alternate host, with

each Xen VM being a cluster node and running a single or multiple number of services.

The Xen hosts can be configured to be part of the same domain, which also allows live

migration of Xen VMs – so if one host server is being heavily loaded, some VMs can be

moved to another host whilst they are still running with no downtime at all.

Notes:

● Optionally, instead of having the Xen VMs belong to the same cluster as the hosts,

the Xen VMs could be setup in their own cluster with each Xen host running their

own cluster, leaving the host cluster to only deal with the Xen VM as a whole. See

the Xen section of this document for details on advantages/disadvantages with this

method.

Suitable Environments:

● Ideal for hosting providers

● Ideal for large companies to increase server utilisation and availability.

● Ideal for IT companies that need large number of servers for various application and

development needs.

8.4 Geographically distributed clusters

All the cluster designs show have been for use in one physical location – the cluster nodes

are all sitting in a rack, connected via ethernet, and is able to support floating IP addresses

because there is only one route into the cluster.

However, a common desire is to have geographically distributed clusters to prevent failure of

a single site taking the whole cluster offline.

Typical uses for this might be:

● A company with offices in two cities would like to have one server at each office

with the data mirrored between them.

● An ecommerce website wanting replicated email, website and database services

between two sites to ensure availability.

However, there are some big issues with a geographically separated cluster that need to be

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Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.1 Instrukcja Użytkownika Strona 28