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C122-B001-02EN
CHAPTER 9 Clustering
z
Network configuration
The nodes that belong to a cluster are connected via a dedicated LAN to ensure that
they can monitor errors encountered by any of the other nodes and that data
consistency can be maintained among the nodes. This network is called a private
network. In contrast, the LAN used for business operations is called a public
network.
9.3.2
Virtual server
A virtual IP address instead of the IP address of a node is used as the IP address for
access to business application software, because it is not affected by business
application operations on any node. The server whose virtual network name is
associated with the virtual IP address is called a virtual server. The virtual server can
be referenced from clients as a Windows network computer.
As a rule, clients access the application software via a virtual server. During
switching from a node on which business application software is running, the
corresponding session is disconnected once. However, the session can be resumed by
reestablishing the connection to the same virtual server after the business application
software restarts.
Because of this mechanism, clients in a cluster system need not consider the particular
node on which business application software is running.
Figure 9.8 Virtual server
9.3.3
Scope of remedies
Remedies can be found for hardware (e.g., CPUs, motherboards, and LAN cards)
failures and software failures (e.g., application errors). Note that a server cluster is
not a fault tolerant (FT) system. If a business application failover occurs, operation
stops for a short time.
Node 1
Node 2
Virtual server: Server A
Clients
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