Red Hat ENTERPRISE LINUX 4 - VIRTUAL SERVER ADMINISTRATION Manual

Also see for ENTERPRISE LINUX 4 - DEVELOPER TOOLS GUIDE: Installation guide Installation guide Tuning guide Installation guide Manual

Contents

Chapter 3.19Setting Up LVSLVS consists of two basic groups: the LVS routers and the real servers. To prevent a single point offailure, each groups should contain at least two member systems.The LVS router group should consist of two identical or very similar systems running Red HatEnterprise Linux. One will act as the active LVS router while the other stays in hot standby mode, sothey need to have as close to the same capabilities as possible.Before choosing and configuring the hardware for the real server group, determine which of the threeLVS topologies to use.3.1. The NAT LVS NetworkThe NAT topology allows for great latitude in utilizing existing hardware, but it is limited in its ability tohandle large loads because all packets going into and coming out of the pool pass through the LVSrouter.Network LayoutThe topology for LVS using NAT routing is the easiest to configure from a network layoutperspective because only one access point to the public network is needed. The real servers passall requests back through the LVS router so they are on their own private network.HardwareThe NAT topology is the most flexible in regards to hardware because the real servers do notneed to be Linux machines to function correctly. In a NAT topology, each real server only needsone 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 topology creates anetwork bottleneck at the LVS router, gigabit Ethernet NICs can be employed on each LVS routerto increase the bandwidth the LVS routers can handle. If gigabit Ethernet is employed on the LVSrouters, any switch connecting the real servers to the LVS routers must have at least two gigabitEthernet ports to handle the load efficiently.SoftwareBecause the NAT topology requires the use of iptables for some configurations, there can bea fair amount of software configuration outside of Piranha Configuration Tool. In particular, FTPservices and the use of firewall marks requires extra manual configuration of the LVS routers toroute requests properly.3.1.1. Configuring Network Interfaces for LVS with NATTo set up LVS with NAT, you must first configure the network interfaces for the public network and theprivate network on the LVS routers. In this example, the LVS routers' public interfaces (eth0) will beon the 192.168.26/24 network (I know, I know, this is not a routable IP, but let us pretend there is afirewall in front of the LVS router for good measure) and the private interfaces which link to the realservers (eth1) will be on the 10.11.12/24 network.So on the active or primary LVS router node, the public interface's network script, /etc/sysconfig/network-scripts/ifcfg-eth0, could look something like this:DEVICE=eth0