Server Load Balancing
by: Tony Bourke (Author)
Publisher: O′Reilly
Edition: Illustrated
Publication Date: 13 Aug. 2001
Language: English
Print Length: 192 pages
ISBN-10: 0596000502
ISBN-13: 9780596000509
Book Description
Load balancing improves network performance by distributing traffic efficiently so that individual servers are not overwhelmed by sudden fluctuations in activity. Server Load Balancing is a guide to this critical component of high availability, clustering, andfault tolerance, all of which provide the infrastructure for reliable Internet sites and large corporate networks.Much of the information on load balancing comes from vendor-specific manuals that use inconsistent terminology and are often biased toward the products they cover. Server Load Balancing explains to engineers and technicians the concepts and terminology of load balancing and offers practical guidance for planning and implementing it in almost any environment. It includes a configuration guide with diagrams and sample configurations for installing, configuring, and maintaining products from the four major vendors:Alteon WebSystemsCisco’s CSS Series (formerly ArrowPoint)F5’s BIG-IPthe Foundry ServerIron seriesBy comparing several load balancing products, you’ll gain a deeper understanding of the technology and how best to use it to improve your network performance. No system administrator responsible for traffic management should be without this practical guide.
About the Author
Amazon Review The slender Server Load Balancing explains the state of the art in multiple-server technologies implemented at Layers 4 and 5 on the OSI network model. An increasing number of shops are putting clustering and load-balancing technologies into place so as to provide high availability and an economic way to scale server capacity. Though author Tony Bourke includes a fair bit of good information on configuring four commercial load-balancing solutions, the most valuable part of his work is his high-level discussions of how load balancing fits into a larger network environment, and his explanations of the relative merits of alternative approaches to the problem. A comparison of flat-based solutions with designs based on Network Address Translation (NAT) is part of this book’s value; further appeal takes the form of dozens of network diagrams that document typical working solutions. Bourke shows his familiarity with real-life design constraints by documenting various load-balancing solutions and pointing out what each can do for an organisation–he points out that a host that implements NAT-based balancing solution can double as a firewall, thereby saving some money that would have been required for a dedicated security device. He also provides introductory material on the competing solutions’ administration interfaces, enabling implementers to get a head start on their work without wading into vendor documentation. –David WallTopics covered: The problems presented by requirements for high availability and failover, and the solutions that server load balancing can provide. In addition to general information on flat–and NAT-based load balancing solutions–this book documents strategies for implementing Alteon WebSystems, Cisco CSS, F5 BIG-IP, and Foundry ServerIron. Review ‘This has been well written with clear precise instructions, together with diagrams, on the many subjects, thus ensuring that the network administrator, not only understands the reasons behind the tasks, but also provides clear instructions in a step by step process.’ www.four-runner.com From the Publisher Load balancing distributes traffic efficiently among network servers so that no individual server is overburdened. This vendor-neutral guide to the concepts and terminology of load balancing offers practical guidance to planning and implementing the technology in most environments. It includes a configuration guide with diagrams and sample configurations for installing, configuring, and maintaining products from the four major server load balancing vendors.
About the Author
Tony Bourke is a private consultant specializing in Unix administration, networking, and load balancing. He has held positions at SiteSmith, GlobalCenter, and Digex. Tony has designed and implemented SLB and Unix architectures for many high-profile and high-traffic web sites. He has published articles in Sys Admin Magazine, Hostingtech Magazine, and Network World. He is one of the leading authorities on the topic of server load balancing and frequently speaks at conferences around the country. He can be reached at tony@vegan.net. Excerpt. © Reprinted by permission. All rights reserved. Chapter 7 – NAT-Based SLB Network ArchitectureNAT-based SLB network architecture is, by definition, any SLB network implementation where the IPs of the VIPs and real servers are on different subnets. It is named NAT because the load balancer NATs packets traveling between two subnets, much like a firewall or a router performing a NAT. ImplementationThe main difference between NAT- and flat-based architectures is that the SLB unit performs a NAT from one network to another. The best and most typical way to implement NAT-based SLB is with a route-path, two-armed configuration.In this configuration the servers are on a separate VLAN from the VIP addresses on the load balancers. On the public network, the only floating IPs between the active and standby load balancers are the VIP addresses. There is no need for a floating default gateway (such as 192.168.0.10 in the flat-based example) on the public network, since the load balancers aren’t acting as default routes on that network. The floating gateway is included on the private network (10.0.0.1 in the following figures). The load balancers can also function as firewalls because they have such tight control over traffic flow.Sometimes NAT-based SLB is implemented, but, in this method, all devices share one LAN. The load balancers are configured for multiple networks on the same LAN, and they perform the NAT themselves. The load balancers are configured for two subnets on the same LAN, one for the public interfaces for the VIPs, and another for the web server’s private subnet. Even though everything is on the same LAN, the load balancer still performs the NAT. From both a security and an architectural standpoint, it’s better to use a two-armed configuration with two separate LANs (or two VLANs). Putting everything on one LAN defeats several of the security objectives and advantages of a NAT-based configuration. Keeping an actual barrier between the server and public network reinforces the overall security of a site. Traffic flow is easier to manage with two (V)LANs as well. There is a clear delineation and demarcation point for the two separate networks, making troubleshooting, in many cases, much easier.Bridge-Path and DSRBecause NAT from one network to another is a Layer 3 function, bridge-path isn’t an option for NAT-based SLB. For NAT to work, the load balancer must have interfaces on two networks, and bridge-path generally involves only one network.DSR is not as common in a NAT-based scenario as it is in a flat-based setup, but it is possible. Unlike flat-based scenarios, a Layer 3 device is required in addition to the load balancer and Layer 2 infrastructure to work with DSR. As per a DSR scenario, the packets have already been rewritten on the way out of the actual servers with no need for any more processing. The Layer 3 device simply forwards the packets from one network to another–a process that is resource-intensive but saves the load balancer some work. The redundancy component was removed to better show how DSR would fit into this type of scenario. A packet comes to the load balancer (step 1) and is sent to a web server, such as ws-3 (step 2). The web server then sends the packet out already rewritten (step 3), but it still needs to be forwarded to the public network so it can get to the Internet. The Layer 3 device forwards the packet unchanged to the public network and then on to its destination (step 4), without adding any additional load to the load balancer. The actual load on the Layer 3 device is minimal, since all it is doing is forwarding packets with no processing.Why NAT-Based?There are several advantages to NAT-based SLB, most of which involve the extra security that a NATed connection can provide, especially when the servers are on a nonrouted RFC 1918 address space. When dealing with servers on a nonrouted IP space, you have a great deal of control over how the servers are actually seen by the world. This architecture lends itself well to a site where the majority of traffic is HTTP (or SSL). With the added security of the NATed IPs and the relatively low in-out ratio (approximately 10 packets out for every packet in with HTTP traffic, while hundreds of packets go out for every packet in with streaming), the NAT-based architecture can provide an additional measure of security and performance. Web and SSL applications both work well with NAT.
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