the services and applications from other nodes in the cluster in the event of planned
failover of services or server failure, or if applications are stopped for maintenance
purposes.
The cluster consists of numerous nodes that can be active or passive. An active node is
simply a node that currently owns a service or application. Windows Server 2012 and
above allow up to 64 nodes in a cluster, up from the 16 nodes in previous versions of
Windows Server.
A cluster can contain multiple services and applications, and these can be spread
among all of the nodes in the cluster. A service or application consists of various
resources that enable the service or application to function, such as a disk resource, a
share, a name, and an IP address. Different types of services and applications use
different resources.
Any resource that is cluster aware and hosted in a cluster can move between nodes in
the cluster to increase its availability. In an unplanned failure, such as a node failing, a
small period of service interruption may occur, because the node failure must be
detected and then the service’s resources moved to another node and restarted. In
most planned scenarios, such as moving resources from one node to another to enable
maintenance on the source node, any outage can be avoided, such as using Live
Migration when a Hyper-V virtual machine moves between nodes in a cluster.
If you used clustering prior to Windows Server 2008, then you will have experienced
an extremely long and painful cluster creation process that required pages of
configuration information, was hard to troubleshoot, and required special hardware
from a cluster-specific hardware compatibility list. This completely changed with
Windows Server 2008. Windows Server 2008 introduced a greatly simplified cluster
creation process that required you to specify only the nodes to be added to the cluster
and to provide a name for the cluster and an IP address if DHCP was not used. All the
other details are automatically configured by the cluster setup wizard. Additionally,
the separate cluster hardware compatibility list was removed, replaced with a new
cluster validation process that is run on the desired nodes prior to cluster creation. If
the cluster validation passes, the cluster will be supported by Microsoft.