HP XC System Software Administration Guide Version 3.2

1.8.1 Linux Virtual Server for HP XC Cluster Alias
The HP XC system uses the Linux Virtual Server (LVS) to present a single host name for user
logins. LVS is a highly scalable virtual server built on a cluster of real servers. By using LVS, the
architecture of the HP XC system is transparent to end users, and they see only a single virtual
server. This eliminates the need for users to know how the cluster is configured in order to
successfully log in and use it. Any changes in the system configuration are transparent to end
users. LVS also provides load balancing across login nodes, which distributes login requests to
different servers.
Figure 1-3 illustrates the use of LVS in an HP XC system.
Figure 1-3 LVS View of Cluster
1.8.2 Network Time Protocol
One node in an HP XC system acts as the internal Network Time Protocol (NTP) server for all
the other nodes. By default this is the head node. All other nodes are NTP clients of this server.
You can specify where the internal NTP server gets the time. You can specify up to four external
time sources if the internal server has a connection to an outside network. You can also choose
to use the internal server's own clock as the time source.
If something goes wrong and you notice a problem with the clocks synchronizing on any nodes,
verify the internal server's /etc/ntp.conf file and the ntp.conf file on the nodes that are
experiencing the problem.
Other tools, such as ntpq and ntpdc, are also available. For more information, see ntpd(1),
ntpq(1), and ntpdc(1) and the ntp.conf file.
1.8.3 Network Address Translation
The HP XC system uses Network Address Translation (NAT) to enable nodes in the HP XC
system without direct external network connections to open outbound network connections to
external addresses. NAT enables application nodes to access network-available resources without
the additional network management, resources, or load of making application nodes part of an
external public network.
1.8.4 Network Information Service
The configuration of Network Information Service (NIS) on an HP XC system is an optional step
that is useful for easing user management and helpful for SLURM and LSF-HPC with SLURM
use. You may decide to set up your user management with some other software, such as
Lightweight Directory Access Protocol (LDAP).
42 HP XC Administration Environment