Server Load Balancing phần 1 pdf

[...]... nslookup www.vegan.net Server: ns1.vegan.net Address: 19 8 .14 3.25 .15 Name: www.vegan.net Addresses: 208 .18 5.43.202, 208 .18 5.43.203, 208 .18 5.43.204 The end result is that the traffic destined for www.vegan.net is distributed between the three IP addresses listed, as shown in Figure 1- 2 Figure 1- 2 Traffic distribution by DNS-based load balancing Chapter 1: Introduction to Server Load Balancing This seems... Theories of Server Load Balancing 1 Introduction to Server Load Balancing While Server Load Balancing (SLB) could mean many things, for the purpose of this book it is defined as a process and technology that distributes site traffic among several servers using a network-based device This device intercepts traffic destined for a site and redirects that traffic to various servers The load- balancing process... or even hundreds of servers operating behind a single URL In Figure 1- 1, we see the simplest representation of SLB Figure 1- 1 SLB simplified Chapter 1: Introduction to Server Load Balancing A load balancer performs the following functions: • Intercepts network-based traffic (such as web traffic) destined for a site • Splits the traffic into individual requests and decides which servers receive individual... servers then make the requests to the authoritative DNS servers and cache the received information Figure 1- 3 shows a typical failure scenario with DNS-based load balancing Figure 1- 3- A failure scenario with DNS-based load balancing The lack of DNS update speed is also an issue when demand increases suddenly, and more servers are required quickly Any new server entries in DNS take a while to propagate, which... For instance, let's say you had three web servers with IP addresses of 208 .18 5.43.202, 208 .18 5.43.203, and 208 .18 5.43.204 that we wanted to share the load for the site www.vegan.net The configuration in the DNS server for the three IP addresses would look like this: www.vegan.net IN IN IN A A A 208 .18 5.43.202 208 .18 5.43.203 208 .18 5.43.204 You can check the effect using a DNS utility known as nslookup,... with it Some sites lose thousands of dollars or more in revenue for Chapter 1: Introduction to Server Load Balancing every minute their sites are unavailable SLB evolved from this need A load balancer works by taking traffic directed at a site One URL, one IP address, and the load balancer distribute the load They balance the load by manipulating the network packets bound for the site and usually do... the serving power of a site is to add more servers This can be very economical, since many small- to medium-sized servers can be much less expensive than a few high-end servers Also, when site load increases, servers can be brought up immediately to handle the increase in traffic Load balancers started out as PC-based devices, and many still are, but now loadbalancing functions have found their way into... which it runs Also, beefing up a server requires taking the server down, and downtime is a concern that server upgrades don't address Even the most redundant of server systems is still vulnerable to outages DNS-Based Load Balancing Before SLB was a technology or a viable product, site administrators would (and sometimes still do) employ a load- balancing process known as DNS round robin DNS round robin... the information 4 The root servers reply back with an authoritative DNS server for the requested hostname 5 The DNS server makes a query to the authoritative DNS server and receives a response Caching issues Many of the limitations of DNS round robin are caused by DNS caching To prevent DNS servers from being hammered with requests, and to keep bandwidth utilization low, DNS servers employ quite a bit... concerning this book to the publisher: O'Reilly & Associates, Inc 10 1 Morris St Sebastopol, CA 95472 (800) 998-9938 (in the U.S or Canada) (707) 829-0 515 (international/local) (707) 829- 010 4 (fax) We have a web page for this book, where we list errata or any additional information You can access this page at: http://www oreilly com/catalog/serverload To ask technical questions or comment on the book, send . of Server Load Balancing 1 1. Introduction to Server Load Balancing 3 In the Beginning 4 Evolution 7 Other Technologies 8 2. Concepts of Server Load Balancing 13 Networking Basics 13 Server Load. CLI 10 0 Getting Started 10 1 Security 10 3 Flat-Based SLB 10 4 NAT-Based SLB 10 8 Redundancy 11 4 Syncing Configurations 11 7 Table of Contents Administration Network 11 7 Additional Features 11 8 10 BIG-IP 11 9 Getting Started 11 9 Flat-Based SLB 12 5 NAT-BasedSLB 12 6 Redundancy 12 7 11 . Foundry Serverlron Series 12 9 Command Line Interface (CLI) 13 0 Flat-Based SLB 13 3 NAT-BasedSLB 13 5 Redundancy 13 6 TV.