IP Load Balancing (Piranha)
Red Hat Enterprise Linux AS has two distinct types of integrated clustering functionality: IP Load Balancing and Cluster Manager.
IP Load Balancing (often known by its project name, Piranha) provides the ability to load-balance incoming IP network requests across a farm of servers. IP Load Balancing is based on Open Source Linux Virtual Server (LVS) technology, with significant Red Hat enhancements.
The following excerpts from the IP Load Balancing documentation provide an overview of its basic operation:
Load-Balancing Clusters Using IP Load Balancing Servers
An IP Load Balancing (IPLB) cluster appears as one server, but, in reality, a user from the Web is accessing a group of servers behind a pair of redundant IPLB routers. An IPLB cluster consists of at least two layers. The first layer is composed of a pair of similarly configured Red Hat Enterprise Linux AS systems. One of these nodes acts as the active IPLB router (the other acts as a backup), directing requests from the Internet to the second layer--a pool of servers called real servers. The real servers provide the critical services to the end-user while the LVS router balances the load to these servers.
The active router serves two roles in the cluster:
- To balance the load on the real servers.
- To check the integrity of the services on each of the real
servers.
The figure shows a simple IPLB cluster consisting of two layers. On the first layer are two IPLB routers. The active system directs traffic from the Internet to a variable number of real servers on the second layer, which in turn provide the necessary services.
The simple, two-layered configuration used in the figure is 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 between each node. If high-availability shared data access and update is required, a third layer is added to the topology. Red Hat Enterprise Linux AS Cluster Manager is ideal for this purpose, so both clustering types can be used together to create, for example, a high availability 3-tier solution with full transactional capabilities.
More high-availability information:
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