Specifications

TWCB Overview
April 16, 2009 Page 4 of 14
The Server Farm
Theserverfarmconsistsofalogicalgroupingofcache‐servers.Eachserverfarmbelongstoa
web‐cache.TWCBsupportstheconfigurationofupto5serverfarmsthatcanbeassociatedwith
theweb‐cache.
Therearethreeaspectstoconfiguringaserverfarm:
• Creatingtheserverfarm
• Associating
oneormorecache‐serverswiththeserverfarm
• Optionallyconfiguringsomeuserstobemembersofaround‐robinlistonthatserverfarm.
Youcreateaserverfarmbynamingit.Uponnamingaserverfarm,youareplacedinweb‐cache
serverfarmconfigurationmode.Withinthiscommandmode
youcanassociateupto128
cache‐serversacrossallserverfarms.Thecacheserveristhephysicalserveronwhichtheend‐user
cacheiscreated.
Thedefaultbehaviorisfortheroutertoselectacacheserveronwhichasinglecacheperend‐user
willreside.All
webobjectscachedforthatend‐userwillusethatsinglecache.Thisdefault
behaviorissufficientforend‐userswithmoderateorlightwebusage.Shouldasinglecacheserver
beassociatedwithoneormoreheavywebusers,cacheserverresourcescaneasilybe 
overwhelmed.Thepredictorround‐robin
loadbalancingfeaturehelpsaddressthisissue.
InFigure 2weseehowanend‐user,configuredforstandardcaching,onlyaccessescachedweb
objectsfromthecacheserverwhereitscacheresides.Inthiscase,theend‐usercacheresidesonthe
s1Serverserverfarm186.89.10.51cacheserver.Thes2Serverserver
farmisconfiguredwitha
predictorround‐robinlist.Eachlistmemberhas itswebobjectscachedacrossallthecache‐servers
onthes2Serverserverfarm.
Figure 2 Predictor Round-Robin Overview
Global
Internet
Predictor Round-Robin
Initial Web Object Request
Initial Web Object Response
All Subsequent Requests for
the same object
Web Site Host
Cache1
186.89.10.51
186.89.10.55
List Members
Standard Caching
Behavior
176.89.10.20
176.89.10.32
176.89.10.45
176.89.10.50
176.89.10.52
Cache Servers
Server Farms
s1Server
s2Server
Router