CS433/533 Computer NetworksOutlineAdminRecap: High-Performance Network ServersRecap: Operational LawsRecap: Why Multiple Network Servers?Recap: Load Direction: Basic ArchitectureRecap: Load DirectionNetwork Path PropertiesNetwork Path Properties: Improve ScalabilityServer SelectionSlide 12Basic Direction MechanismsDirection Mechanisms are Often CombinedExample: NetflixExample: Netflix Manifest FileSlide 17Example: Wikipedia ArchitectureSlide 19DNS Indirection and RotationExample: Amazon Elastic Cloud 2 (EC2) Elastic Load BalancingDetails: Step 1Details: Step 2Details: Step 3DiscussionSlide 26Clustering with VIP: Basic IdeaBig PictureVIP ClusteringLoad Balancer (LB): Basic StructureProblemSolution 1: Network Address Translation (NAT)Example Virtual Server via NATLB/NAT FlowSlide 35SLB/NAT Flow: DetailsLB/NAT Advantages and DisadvantagesLB with Direct ReplyLB/DR ArchitectureWhy IP Address Matters?ARP ProtocolARP in ActionLB/DR ProblemLB via Direct RoutingLB/DR Advantages and DisadvantagesExample Implementation of LBSlide 47Discussion: Problem of the Load Balancer ArchitectureSolutionsMicrosoft NLBSlide 51CS433/533Computer NetworksLecture 12Load Balancing Networks2/16/20121OutlineAdmin and recapLoad balance (direction)oLoad direction mechanismsoDNSoLoad balancer (smart switch)2AdminProgramming assignment 1 status3Recap: High-Performance Network ServersAvoid blocking (so that we can reach bottleneck throughput)threadsLimit unlimited thread overheadthread pool, async ioCoordinating data accesssynchronization (lock, synchronized)Coordinating behavior: avoid busy-waitwait/notify; FSMExtensibility/robustnesslanguage support/design for interfaces4Recap: Operational LawsUtilization law: U = XSForced flow law: Xi = Vi XBottleneck device: largest Di = Vi SiLittle’s Law: Qi = Xi RiBottleneck analysis:5},min{)(max1ZDNDNX},max{)(maxZNDDNR Recap: Why Multiple Network Servers?Scalabilitybeyond single server capability and geolocation of a single serverRedundancy and fault toleranceadministration/maintenance (e.g., incremental upgrade)redundancy (e.g., to handle failures)System/software architectureresources may be naturally distributed at different machines (e.g., run a single copy of a database server due to single license; access to resource from third party) security (e.g., front end, business logic, and database)6Recap: Load Direction: Basic ArchitectureMajor componentsServer state monitoringNetwork path properties between clients and serversServer selection alg.Server routing/adaptation Client direction mechanism7InternetInternetClientSite ASite B?Recap: Load Direction8server statenet path propertybetween servers/clientsserverselectionalgorithmspecificrequest ofa clientnotify clientabout selection(direction mech)server routingNetwork Path PropertiesWhy is the problem difficult?oScalability: if do measurements, complete measurements grow with N * M, where•N is # of sources (e.g., clients)•M is # of destinations (e.g., servers)oComplexity/feasibility in computing path metrics9MNNetwork Path Properties: Improve ScalabilityAggregation:omerge a set of IP addresses (reduce N and M)•E.g., when computing path properties, Akamai aggregates all clients sharing the same local DNS serverSampling and predictionoInstead of measuring N*M entries, we measure a subset and predict the unmeasured pathsoWe will cover it later in the course10M serversN’~100K local DNS serversN~all Internet clientsServer SelectionWhy is the problem difficult?What are potential problems of just sending each new client to the lightest load server?11OutlineAdmin and recapLoad balance (direction)oOverviewoBasic load direction mechanisms12Basic Direction MechanismsApplication layerApp/user is given a list of candidate server names HTTP redirectorDNS: name resolution gives a list of server addressesIP layer: Same IP address represents multiple physical serversIP anycast: Same IP address shared by multiple servers and announced at different parts of the Internet. Network directs different clients to different servers (e.g., Limelight)Load balancer (smart switch) indirectionReverse proxy13Direction Mechanisms are Often Combined14DNS name1IP1IP2 IPnCluster1in US EastCluster2in US WestLoad balancerLoad balancerproxyCluster2in EuropeLoad balancerLoad balancerserversDNS name2Example: Netflix15Example: Netflix Manifest File16Client player authenticate and then downloads manifest file from servers at Amazon CloudExample: Netflix Manifest File17Example: Wikipedia Architecture18http://wikitech.wikimedia.org/images/8/81/Bergsma_-_Wikimedia_architecture_-_2007.pdfOutlineAdmin and recapLoad balance (direction)oBasic load direction mechanismsoDNS19DNS Indirection and Rotation20157.166.226.25routerDNS serverfor cnn.comIP addressof cnn.com157.166.226.25157.166.226.26IP addressof cnn.com157.166.226.26157.166.226.25157.166.226.26157.166.255.18Example: Amazon Elastic Cloud 2 (EC2) Elastic Load BalancingUse the elb-create-lb command to create an Elastic Load Balancer. Use the elb-register-instances-with-lb command to register the Amazon EC2 instances that you want to load balance with the Elastic Load Balancer. Elastic Load Balancing automatically checks the health of your load balancing Amazon EC2 instances. You can optionally customize the health checks by using the elb-configure-healthcheck command.Traffic to the DNS name provided by the Elastic Load Balancer is automatically distributed across your load balanced, healthy Amazon EC2 instances.21http://aws.amazon.com/documentation/elasticloadbalancing/Details: Step 11. Call CreateLoadBalancer with the following parameters:AvailabilityZones = us-east-1aListeners•Protocol = HTTP•InstancePort = 8080•LoadBalancerPort = 80•LoadBalancerName = MyLoadBalancerThe operation returns the DNS name of your LoadBalancer. You can then map that to any other domain name (such as www.mywebsite.com) (how?)PROMPT> elb-create-lb MyLoadBalancer --headers --listener "lb-port=80,instance-port=8080,protocol=HTTP" --availability-zones us-east-1aResult:DNS-NAME DNS-NAME DNS-NAME MyLoadBalancer-2111276808.us-east-1.elb.amazonaws.com 22http://docs.amazonwebservices.com/ElasticLoadBalancing/latest/DeveloperGuide/Details: Step 22. Call ConfigureHealthCheck with the following parameters:LoadBalancerName = MyLoadBalancerTarget =