Red Hat ENTERPRISE LINUX AS 2.1 -, Installation Manual

Page: 121 / 210

Section 8.1:The NAT LVS Cluster 121
8 Setting Up a Red Hat Enterprise Linux
AS LVS Cluster
A Red Hat Enterprise Linux AS LVS cluster consists of two basic groups: the LVS routers and the real
servers. To prevent a single point of failure, each groups should contain at least two member systems.
The LVS router group should consist of two identical or very similar systems running Red Hat Enter-
prise Linux AS. One will act as the active LVS router while the other stays in hot standby mode, so
they need to have as close to the same capabilities as possible.
Before choosing and configuring the hardware for the real server group, you most decide what which
of the three types of LVS topographies to use.
8.1 The NAT LVS Cluster
The NAT topography allows for great latitude in utilizing existing hardware, but it is limited in its
ability to handle large loads due to the fact that all packets going into and coming out of the cluster
pass through the LVS router.
Network Layout
The topography for an LVS cluster utilizing NAT routing is the easiest to configure from a net-
work layout perspective because the cluster needs only one access point to the public network.
The real servers pass all requests back through the LVS router so they are on their own private
network.
Hardware
The NAT topography is the most flexible in regards to cluster hardware because the real servers
do not need to be Linux machines to function correctly in the cluster. In a NAT cluster, each real
server only needs one NIC since it will only be responding to the LVS router. The LVS routers,
on the other hand, need two NICs each to route traffic between the two networks. Because
this topography creates a network bottleneck at the LVS router, gigabit Ethernet NICs can be
employed on each LVS router to increase the bandwidth the LVS routers can handle. If gigabit
Ethernet is employed on the LVS routers, any switch connecting the real servers to the LVS
routers must have at least two gigabit Ethernet ports to handle the load efficiently.
Software
Because the NAT topography requires the use of
iptables
or
ipchains
for some configu-
rations, there can be a fair amount of software configuration outside of
Piranha Configuration
Tool
. In particular, FTP services and the use of firewall marks requires extra manual configu-
ration of the LVS routers to route requests properly.