Scalingterminalservicesarchitecturetomeetthinclientnetwork縮放的終端服務(wù)體系以滿足瘦客戶機網(wǎng)絡(luò)ScalingterminalservicesarchitecturetomeetthinclientnetworkgrowthandclientresourcesreclamationforservicesdistributionSilvestrosN.,PapapanagiotouTh.,IordanakisM.,DilintasG.TechnologicalEducationalInstituteOfPiraeusComputingSystemsEngineeringDepartment250Thivon&P.RalliAve.,Egaleo,Athens,Greece,12244{nsilve,theofilos,mdi,dili}<ΑΤ>oslab.teipir.grNowadaysterminalservicesoptimizetheavailablecomputingresourcesandgreatlyassistadministratorsbysavingtime,duetoeasierinstallation,configurationandmaintenanceoftheserveranddeploymentofapplications.Anotherperspectiveisthecost-savingaspect,sinceinaterminalserverenvironment,allapplicationlogicrunsontheserver,sotheprocessingrequirementsforclientmachinesareminimal.Butevenifclientmachines’requirementsareminimal,personalcomputersthesedaysarepowerfulenoughtoconcurrentlyhandleagreatsetoftasks,soinsuchanenvironment,modernPCsusedasthinclients,havetheirresourceswasted.Inthispaperweattempttoscaleterminalservicestomultipleservers,providingaproperandefficientloadbalancingmethod,whileontopofthatweattempttoutilizeresourcesfromthethinclientsthemselves,inordertomaximizetheefficiencyofthewholeapparatusortogivethecapabilityofusingthemforexternaltasks.Theclientresourcesreclamationisachievedbyformingaclustercomprisingofalltheclientnodes.1.TheenvironmentThenetworkofourOperatingSystemlabconsistedofabout30thinclients,oneterminalserveranda100MbitEthernetconnection.Aftertheadditionofoneextralab(Databases)with15thinclientsandtheR&Dundergroundcenterwith10thinclients,westartedtofaceproblemsoflatency.Therewasalsotheproblemofthesinglepointoffailurecauseifthesingleterminalserverhadproblem,thennoneofthethinclientscouldoperatenormally.Afterthesewedecidedtoupgradeourinfrastracturetoconfronttheproblemsaraised.WeaddedasecondterminalserverandupgradedournetworkinfrastrureusingFibreCablebetweenthethreedifferentclassesandupgradedinternalnetworkinto1Gbitconnection.Afterthesechanges,wecanhavehighavailabilitybasedonactive/passivenodes.Iftheactiveterminalserverfails,thenthepassiveonecouldbeusedautomatically.Theproblemisthattheactivesessionsbetweentherunningthinclientsandtheterminalserverarelost,sothinclientsneedtorebootafterthis.Becauseitisveryimportantforustohaveoursystemsrunningduringtheteachinghours,wealsotriedtoputthetwoterminalserversintoacluster,soifoneofthetwoserverfails,thesessionsandprocessesmigratetotheotherone.2.TechnologiesLTSP(LinuxTerminalServerProject)enablesthin-clientsupporttoLinuxservers.LTSPisaflexible,costeffectivesolutionthatisempoweringourlabs.Weareabletouselow-powerthinclientswhichbootfromaterminalserverandrunanXserverconnectedtotheterminalserver.Thebootprocessofthethinclientsisasfollows.InitiallyeachthinclientsendsaDHCPdiscoverpackettofindtheavailableDHCPserversrunningonthelocalnetwork.ThenanIPaddressisassignedtotheclientfromtheserverandthroughthePXEandTFTPprotocolakernelimageisdownloadedandisexecutedattheclient.Afterthese,eachthinclientcanuseanyfilesneeded,availableattheserver,usingtheNBD(NetworkBlockDevice)protocolwhichgivesthecapabilityofusingtheremoteterminalserverasoneofitsblockdevices.OneofthemailadvantagedusingLTSPisthathelpadministratorstodotheirtasksquicker,duetoeasierinstallation,configurationandmaintenanceoftheserveranddeploymentofapplications.Theyneedtosetupandmaintainonlyoneserverandallthethinclientsarebootedinthasameway.Italsohasalotofadvantagesfromtheclientside.ByusingLDAP,theycanloginfromanythinclientconnectedtotheterminalserverandhavetheirpersonalfilesandsettingsavailable.ErlangisaprogramminglanguagedesignedattheEricssonComputerScienceLaboratoryandhasmanyfeatures.Itsupportsconcurrentprocesseswhichcancommunicatewitheachotherbysendingasynchronousmessages.ItisdesignedtoberuninadistributedenvironmentaswecanhavemanyErlangvirtualmachinesrunningondifferentnodeswhichcancommunicateinexactlythesamewayasprocessesresidingonthesamenode.Italsohasadvancedrobustnesssinceithasvariouserrordetectionprimitiveswhichcanbeusedtostructurefault-tolerantsystemsusingfail-overandmigrationtechniques.Anothergreatfeatureisthatitisallowedprogramcodetobechangedinarunningsystemwithoutstoppingthenodes.Finallyissupportsexternalinterfaceswithwhichcancommunicatewithprogramswritteninotherlanguages.KerrighedisaSingleSystemImage(SSI)operatingsystemforclusters.ItofferstheviewofauniqueSymmetricMultiProcessing(SMP)machineontopofaclusterofstandardPCs.ThegoalsofKerrighedareeaseofuse,highperformanceofapplications,highavailabilityofthecluster,efficientresourcesmanagement,andhighcustomizabilityoftheoperatingsystem.Itsmainfeaturesareclusterwideprocessmanagement,clusterwidesharedmemory,clusterfilesystem,andhighavailabilityforuserapplications.ItsoperationbasedonthesamemaincharacteristicsasLTSPaswehaveacentralserverfromwithallthenodesbootusingthesamebootprocessasLTSPexceptthatinsteadofusingtheNBDprotocoltoaccessfiles,itusestheNetworkFileSystem(NFS).Itsmainadvantagesisthatitsupportsprocessmigrationbetweenclusternodesifonenodefailsortocounterbalancetheresourcesusageofthethinclients.3.LoadBalancingInordertoachievehighavailabilityinLTSP,severalsoftwaremustbeusedinLTSPserverandcooperateeachother.Ourenvironment,needshighavailableresourcesofLTSPservice.ThiscanachievedusingtogetherheartbeatsoftwaretoperformredundancyofaLoadBalancerservice,theloadbalancingserviceitselfcalledldirectord,andthetoolstomanagethislikeipvsadm.Heartbeatlogicbasedonaservicerunningonbothactiveandpassivenodeofacluster.Usuallytheseserversareinterconnectedthroughoneormorecrossovercables.Theactivenodeisrunningtheactualresourcesthatwewanttohavehighavailability,andthepassivenodestaysstandby,sendingandlisteningforaheartbeattoandfromtheactivenode.Whentheactivenodeforsomereasonhaveafailureonrunningtheservice(ex.connectionproblem,softwareproblem)thentheservicefailsovertheothernodeandnamedactivenode.TheactualservicethatperformstheloadbalancingbetweenthenodesofourLTSPclustercalledldirectord.Thisdaemonisusedtosendpacketsonthenodesofaclusterusingdifferentalgorithms.Conceptsconfiguringthisserviceare,checksweshouldconfiguretheclustertoperforminordertodecidewhetheronenodeisrunningtheserviceornotbalancingmethodthattheloadbalancershouldusesoitdistributestheload,onthenodesoftheclusterwiththebestdistributionway,toolsandinterfacetothisbalancersoitcanbeusedeasilyandmonitoritsperformanceInordertouseldirectordserviceweshouldrecompilethelinuxkernelwiththeuseofip_vsmodule.Thismoduleprovidesthekerneltheneededfunctionsovertheipv4/6soitcanmonitoranddistributeanetworktrafficusingdifferentmethodstodifferentnodes.Usingasimpleconfigurationfilewemayassignaclusteripforourclusteredservice,axdmcpcheckforourserviceinthespecificportofit,andconfiguretheRound-Robinmethodtodistributethenetworkloadonournodes.Finallyweinterfacewiththispartofthekernelusingtheipvsadmcommandtochecktheavailabilityoftheserviceandthecurrentandtimedoutconnections.Wemayalsousethistoadd/removenodesonourcluster.Asimplelogfileshouldbemonitoredthroughanalertingmechanismsuchassyslogserviceinordertoknowwhenweshouldtakesomeadministrativemeasures.4.Thereclamationofclientresources4.TheideabehindreclamationofclientresourcesisthatnormallyinanLTSPenvironmentweuseonlytheresourcesoftheterminalserver(twoserversinourcase)sothethinclientsremainidlejustrenninganXserver.Sincethatmodernsystemshasgreatpower,itisagoodideatobeabletousethispower.Inthisway,eachprocesscanbeexecutednotonlyattheterminalserverbutalsoatathinclient,maybedifferentfromwhichthatstartedit.HavingarunningLTSPenviromentforeducationalpurposes[1]allowustousethisasaninftrastructuretoperformmoretasksthanusual.Ourvisionofhavingaresearchactivityarounddistributingandparallelsystemsforceustodeploysomearchitecturesonourcomputernetwork.UsingerlangcomputerlanguagewecontributeourresourcesonalargecomputercloudcalledRainUp,meanwhileusingKerrighedweareabletobuildalargeparallelcomputertoscaleoutsymmetricmultiprocessorapplications.OurLTSPenvironmentusesasingleoperatingsystemimagewhichpassedtoeverythinclientnode.ThisimageresidesintheloadbalancedLTSPcluster.Inthisimage,wehaveinstallederlanginterpretersoeverytimeadisklessstationbootsupusingthisimageitisreadytoperformtasksusingerlanginterpreter.Ontheotherside,onactiveLTSPserver,alistofcurrentconnectednodescanberetrievedsoaserverprocessofacloudcomputernetworklikeRainUpcaneasilyjointheminitsresources.Thetrustedconnectivitybetweenthemandthehighspeednetworkarekeystoprovidesuchasuccessfulimplementation.TheoperatingsystemimagewhichisusedforthebootofdisklessstationinordertoprovidetheneededgraphicmodeandnetworklibrariestoconnecttoXserver,ha