This section describes the basic network configuration and services of a Qlustar cluster.
The IP configuration of the head-node is defined in the file
man interfaces for details), while
/etc/resolv.conf is the key-control file regarding the
DNS configuration (see DNS). Network interfaces can be brought up or
down using the commands
ifdown (see also the corresponding man pages). Typically,
the head-node has at least two network interfaces, one for the external LAN and one for the
internal cluster network. For all cluster-internal networks (boot/NFS, optional Infiniband
and/or IPMI)Network Configuration cluster-internal networks, unofficial (not routed) IP
addresses are used, usually in the range
192.168.x.0/255.255.255.0, while for larger clusters
172.16.y.0/255.255.0.0 is often used. In the latter case,
y might indicate the
The cluster-internal network ranges can be conveniently chosen during installation.
This section describes how to configure the Domain Name System (DNS). The file
/etc/resolv.conf contains the addresses of the DNS servers to use and a list of domain names
to search when looking up a short (not fully qualified) hostname. Example:
search your.domain nameserver 127.0.0.1
where 127.0.0.1 is the localhost address and your.domain is the DNS domain name.
The basic IP configuration of the compute-nodes is done using the Dynamic Host Control Protocol
(DHCP). The DHCP server is not only responsible to automatically supply the IP address and
netmask to these nodes, but also additional configuration options like the gateway and DNS
server addresses, DNS domain name and many other parameters. Starting from Qlustar 11.0,
dnsmasq is also used to provide DHCP services. The corresponding configuration file is
/etc/dnsmasq.d/01-dhcpd.conf and is auto-generated by QluMan.
If a cluster has additional internal networks (e.g. Infiniband), the IP address of a node in that network is derived from its basic DHCP address and set automatically during boot. The addresses of additional networks can be specified during installation and in QluMan. Check the QluMan Guide for more details.
To allow direct TCP/IP connections for the compute-nodes to machines outside of the internal cluster network, IP masquerading (NAT) is configured by default on the head-node(s) during installation. This might be necessary e.g., when applications running on the compute-nodes need to contact a license server in the public LAN.
All IP packets with unofficial sender IP addresses and a destination in the public LAN are then
translated by the head-node to packets with its own official IP address. When a reply packet
arrives, it is translated back to the unofficial IP address of the originating node inside of
the cluster. The head-node works as a router in this case. The following example section in
/etc/network/interfaces (cluster network address is 192.168.97.0/24) shows, how masquerading
is activated on boot and disabled on shutdown:
iface br-ext inet static address 192.168.55.44 netmask 255.255.255.0 broadcast 192.168.55.255 gateway 192.168.55.254 dns-nameservers 127.0.0.1 bridge_ports enp0s4 bridge_stp off bridge_fd 0 bridge_maxwait 0 up iptables -t nat -A POSTROUTING -s 192.168.97.0/24 \ -o br-ext -j MASQUERADE down iptables -t nat -D POSTROUTING -s 192.168.97.0/24 \ -o br-ext -j MASQUERADE
Synchronized system time throughout the cluster is crucial for its flawless operation. It is
achieved using the Network Time Protocol (NTP) daemon. If the head-node has direct Internet
access, publicly available time-servers on the Internet can be contacted and used as an
accurate time reference. In order to set a list of time-servers, edit the file
and add a line for every ntp-server (example ntp-1) to be contacted: