Three-Tier Lvs Topology - Red Hat ENTERPRISE LINUX 4 Manual

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Three-Tier LVS Topology

• Source Hash Scheduling — Distributes requests to the pool of real servers by looking up the source

IP in a static hash table. This algorithm is for LVS routers with multiple firewalls.

Also, the active LVS router dynamically monitors the overall health of the specific services on the real

servers through simple send/expect scripts. To aid in detecting the health of services that require

dynamic data, such as HTTPS or SSL, you can also call external executables. If a service on a real

server malfunctions, the active LVS router stops sending jobs to that server until it returns to normal

operation.

The backup LVS router performs the role of a standby system. Periodically, the LVS routers exchange

heartbeat messages through the primary external public interface and, in a failover situation, the

private interface. Should the backup LVS router fail to receive a heartbeat message within an

expected interval, it initiates a failover and assumes the role of the active LVS router. During failover,

the backup LVS router takes over the VIP addresses serviced by the failed router using a technique

known as ARP spoofing — where the backup LVS router announces itself as the destination for IP

packets addressed to the failed node. When the failed node returns to active service, the backup LVS

router assumes its backup role again.

Figure 1.21, "Two-Tier LVS Topology"

The simple, two-tier configuration in

is suited best for clusters

serving data that does not change very frequently — such as static web pages — because the

individual real servers do not automatically synchronize data among themselves.

1.8.2. Three-Tier LVS Topology

Figure 1.22, "Three-Tier LVS Topology"

shows a typical three-tier LVS configuration. In the example,

the active LVS router routes the requests from the public network (Internet) to the second tier — real

servers. Each real server then accesses a shared data source of a Red Hat cluster in the third tier

over the private network.

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