B2-负载均衡基本原理

负载均衡基本原理王文angwnb@单台服务器到多台服务器的转变InternetBIG-IPLTMsClientsServersClientsInternetServers什么是服务器负载均衡12345678ClientsClientsInternet虚拟服务器与网络地址转换

VirtualServer&NAT真实服务器RealServer网络地址转换VirtualServerAddress7:80Internet:8080:8080:8080:8080RealServerAddress7:80Internet虚拟服务器数据流-Packet#1Internet:8080:8080:808:8080域名IP地址7VirtualServerAddress7:80数据流-Packet#1LTM根据负载均衡把数据包的目的地址转换成Node的地址InternetPacket#1Src-0:4003Dest–7:80:8080:8080:8080:8080Packet#1Src–0:4003Dest–:808007:80数据流–Packet#1响应包

LTM把数据包的源地址转换成VirtualServer地址InternetPacket#1-returnDest-0:4003Src–7:80:8080Packet#1-returnDest–0:4003Src–:808007:80:8080:8080:8080数据流-Packet#2InternetPacket#2Src-1:4003Dest–7:80:8080Packet#2Src–1:4003Dest–:808017:80:8080:8080:8080数据流–Packet#2回包

InternetPacket#2-returnDest-1:4003Src–7:80:8080Packet#2-returnDest–1:4003Src–:808017:80:8080:8080:8080数据流-Packet#3InternetPacket#3Src-5:4003Dest–7:80:8080Packet#3Src–5:4003Dest–:808057:80:8080:8080:8080数据流–Packet#3回包

InternetPacket#3-returnDest-5:4003Src–7:80:8080Packet#3-returnDest–5:4003Src–:808057:8080:8080:8080ConnectionTable连接表SrcIPAddressVirtualServerRealServer0:40037:80:80801:40037:80:8080………0:40057:80:80801:40087:80:80805:40037:80:8080SrcIPAddressVirtualServer0:40037:801:40037:80……0:40057:801:40087:805:40037:80客户端Netstat-na负载均衡器BconnConnectionTable连接表SrcIPAddressVirtualServerRealServer0:40037:80:80801:40037:80:8080………0:40057:80:80801:40087:80:80805:40037:80:8080SrcIPAddressRealServer0:4003:80801:4003:8080……0:4005:80801:4008:80805:4003:8080服务器端Netstat-na负载均衡器BconnF5负载均衡的基本构件

Pool、PoolMembers与NodesInternet:8080:80:4002:80PoolMembersNodes是指PoolMembers的IPAddressPools,PoolMembersandNodesNode=IPaddress:80:80:80PoolMember

=Node+PortPool

=GroupofpoolmembersPoolMembers的端口与地址问题Internet:8080:80:4002VirtualServer7:80PoolMembers注意：1、PoolMember的端口可以不一样2、PoolMember不一定需要与BIG-IP相连或在同一网段3、一个Pool中PoolMember的数量不受限，现网有达上百个的实例:80/24/24路由器虚拟服务器VirtualServerInternet:8080:4002:80VirtualServerIPAddress+Service(Port)区分端口可以为Any(0)准备了负载均衡器是否需要对流过的网络流量作处理一般与Pool相关联一台负载均衡器支持的Virtualserver的数量不受限，现网有达上千个的实例7:80如何选择服务器--负载均衡算法RoundRobinRatioLeastConnectionsFastestObservedPredictiveDynamicRatioPriorityGroupActivationFallbackHostStaticDynamicFailureMechanisms轮询--RoundRobinClientsRouterBIG-IPLTMControllerServersClientrequestsaredistributedevenly12345678Internet比率--RatioClientsRouterBIG-IPLTMControllerServersAdministratorsetsratiofordistributingClientrequests3:2:1:11234891011Internet571214613最小连接数--LeastConnectionsClientsRouterBIG-IPLTMControllerServers12InternetNextrequestsgoestoNodewithfewestopenconnections459460461470CurrentConnections3456最小连接数--LeastConnectionsClientsRouterBIG-IPLTMControllerServersInternetSometimelater,numberofconnectionschange6163280290111112CurrentConnections62最快回应--FastestClientsRouterBIG-IPLTMControllerServersNextrequestsgotoNodewithfastestresponsetime25Internet10ms10ms10ms17msCurrentResponseTimes1436最快回应--FastestClientsRouterBIG-IPLTMControllerServersSometimelater,responsetimeschange102104Internet10ms10ms7ms7msCurrentResponseTimes101103服务器健康检查HealthMonitors

如何识别不可用的服务器

Internet:80服务健康检查MonitorConcepts网络连通性检查AddressCheckNode–IPAddress端口ServiceCheckIP:port内容检查ContentCheckIP:portpluscheckdatareturned交互式检查InteractiveCheck网络连通性检查--AddressCheckStepsPacketssenttoIPAddressesIfnoresponse,thennotrafficsenttomembersusingthatnodeaddressExample-ICMPInternetICMP服务端口检查--ServiceCheckStepsOpensTCPconnection(IPAddress:service)ConnectionclosedIfTCPconnectionfails,thennotrafficsenttoassociatedMembersExample–TCPInternet:80:80:80TCPConnection内容检查--ContentCheckInternet:80:80:80StepsOpensTCPconnection(IPAddress:service)SendsarequestResponsereturnsdataConnectionclosedIfReceiveRulenotfoundindata,thennotrafficsenttoassociatedMembersExample–httphttpGET/交互式检查--InteractiveCheckInternet:80:80:80StepsOpensTCPconnection(IPAddress:service)Interactiveconversationtosimulatereal-worldConnectionclosedIfexpectedresultsdonotoccur,thennotrafficsenttoassociatedMembersExample–SQLrequestconversation会话保持Persistence123123ConnectionTable连接表SrcIPAddressVirtualServerRealServer0:40037:80:80801:40037:80:8080………0:40057:80:80801:40087:80:80805:40037:80:8080SrcIPAddressRealServer0:4003:80801:4003:8080……0:4005:80801:4008:80805:4003:8080服务器端Netstat-na负载均衡器BconnSourceAddressPersistenceTableSrcIPAddressVirtualServerRealServer0:40037:80:80801:40037:80:8080………0:40057:80:8080???1:40087:80:8080???5:40037:80:8080SrcIPAddressRealServer01……5PersistenceTable负载均衡器源地址会话保持--SourceAddressPersistence根据client的源P地址Netmask->AddressRange12312301IfNetmaskis07CookiePersistenceInsertmodeBIG-IPLTMInsertsacookieintothestreamRewritemodeWebservercreatescookieandBIG-IPLTMchangesitPassivemodeWebservercreatescookieandBIG-IPLTMreadsitClientServerHTTPrequest(nospecialcookie)TCPhandshakeTCPhandshakeHTTPrequest(nospecialcookie)HTTPreply(nospecialcookie)HTTPreply(withinsertedcookie)pick

serverHTTPrequest(withsamecookie)TCPhandshakeTCPhandshakeHTTPrequest(nospecial

cookie)HTTPreply(nospecialcookie)HTTPreply(updatedcookie)cookie

specifies

serverFirstHitSecondHitCookieInsertMode源地址转换SNATs

Internet02多对一的转换Many-to-onemappingTraffictoSNATAddressisrefusedCanshareIPwithVirtualServerSNATs–典型数据流

Internet02:400103:8002:3300103:80源地址会转换成SNAT的地址请注意源端口Server03:80SNATs–数据流的回包

InternetSNATIPAddress0203:80:400103:80

02:33001数据流的回应包地址会转换回来Server03:80SNATTable