Radware会话保持.doc

会话保持会话保持就是要确保单个应用会话的所有流量发送到同一服务器。会话保持通常是基于源地址、源地址和源端口进行保持。但是有时侯仅这些信息是不够的，比如在会话过程中客户端的IP地址改变，或者多个TCP连接属于同一逻辑会话，并且必须发送到同一服务器。在这种情况下，WSD必须通过应用标识区别会话，而不是三层（IP地址）和四层（TCP/UDP端口）信息。WSD能够看到应用层会话标识，跟踪这些标识，确保相同标识的数据发送到同一服务器。WSD支持下列方法保持应用层会话：=Session ID保持提供了一种灵活机制，根据HTTP流量中的不同条件保持HTTP流量；=SSL ID 专门问跟踪SSL会话设计；=MS Terminal Servers会话保持专门针对Microsoft 终端服务器；=哈希分发方法，根据四层客户表维持客户IP保持，或者联合七层策略维持基于URL保持；Session ID 保持Session ID保持功能是专门为HTTP会话设计的，他能够让WSD把所有具有相同会话标识的服务请求发送到同一服务器。Session ID保持工作在第七层，基于HTTP会话标识保持服务器。为了定义HTTP包头中哪部分信息标识会话，WSD提供了灵活的配置机制。比如会话标识符能够作为HTTP包头中URL参数的一部分，等等。通过Session ID保持，WSD通过Session ID区分会话是否来自同一客户端。在HTTP会话中，WSD检查访问FARM的流量，根据保存在HTTP包头中的Session ID选择服务器，WSD用保持标识符在HTTP报头中查找Session ID，这个保持标识符能够基于每个FARM定义。保持优先级机制 在处理服务器选择过程中，WSD采用下列保持优先级：1. Session ID2. Source TCP port3. Source IP address如果在HTTP报头中没有会话信息，根据预先定义的会话模式选择服务器： 默认模式下，当目的端口要求Session ID保持的TCP流量到达一个FARM地址，WSD强行实现Entry per session模式，参考表格4-8。这意味着这种流量的服务器选择基于Session ID，如果没有Session ID，根据客户端ID保持选择服务器。其他到FARM的流量继续在客户表中按默认模式反映。 当选择server per session 模式，对于没有Session 信息的新会话，WSD选择最佳的服务器。 当选择Entry per session 模式，WSD根据源端口号码分发没有会话信息的请求。每个新会话由源端口和源IP地址标识。基于源地址的会话保持由客户表机制维护。Note: 必须配置每个FARM的Session ID 保持。动态和静态会话标识保持机制 会话标识保持能够动态或静态设置。动态会话标识WSD从服务器应答中动态学习会话标识的内容。静态机制意味着你必须为每个服务器配置会话标识。 动态会话标识保持 当采用动态会话标识保持，服务器应答中包含了会话标识。保证带有相同会话标识的流量到来时选择相同的服务器。会话标识在WSD的内存中保存一段时间，具体由Inactivity Timeout参数定义。在这段时间，无论何时具有相同会话标识的客户端访问，WSD把客户端的请求发送到相同的服务器，而不考虑客户端的IP地址。Table 4-8 说明了动态会话标识保持的参数 Parameter DescriptionFarm Address 采用会话标识保持的FARM的IP地址 Application Port 截取流量会话ID信息的的TCP端口，0表示所有端口。默认是0.Lookup Mode查找模式定义了请求中会话标识出现的位置。Lookup Mode的可能值为： 报头：表示WSD查找HTTP报头，用分隔符：分隔用于服务器保持的保持标识符和值。 Indicator: 表示WSD查找用于保持服务器的用分隔符=分隔的保持标识和内容。 RegExp: 表示WSD查找HTTP报头中预先定义的常规表示符。Default value is Indicator.For example: set Lookup Mode to Header andPersistency Identifier to WWW-AuthenticateHTTP Header field. Another example, setLookup Mode to Key and PersistencyIdentifier to JSESSIONID, when using serverpersistency with Weblogic servers.Persistency Identifier标识符的名称，最多64个字节，大小写敏感。 Identifier MatchI表示摄制的标识符内容是否匹配标识符名称，或者只是作为一个前缀，允许跟随其他字符。可以是完全匹配或者前缀。 Value Offset偏移量标识会话ID的内容是否紧跟着保持标识符名称。默认是0，意味着会话ID内容紧跟着会话标识符的名称和分割符。内容偏移量用于保持标识符由一个动态值和一个静态值组成。WSD忽略服务器保持的动态前缀。比如标识内容由时间戳和客户ID组成，只用客户端ID进行服务器保持。Value Max Length会话ID内容的最大长度。Possible values: 1 to 256, default is 256. Stop Chars表示会话ID内容结束的字符。默认是;. 最多10个字符。中间不需要分隔。All white space, including white blank, tab, enter, and so on, are also considered a Stop Character.Inactivity Timeout（Second）Defines how long the association of SessionID values to servers should be kept when notraffic with this Session ID value is passingthrough WSD. The mechanism is similar toAging Time in the Client Table. Possiblevalues: 1 to 65,535 seconds (18.2 hours),default is 60 seconds.Learning DirectionThis parameter indicates which traffic isinspected by WSD both in order to gatherpersistency information and in order to usethat information for a specific session.Possible values: Server Reply means WSD dynamicallylearns which session IDs are to beassociated with each server, according toinformation in replies from servers. WSDinspects also client requests, to find if theycontain a session ID that was alreadylearned by WSD, to forward them to thecorrect server accordingly. Client Request can be used whenSession IDs appear only in requests fromclients, and means that WSD does notinspect replies from servers. This can beused, for example, when persistency isbased on client IP that appears in XForwarded-For HTTP header, or whenonly static values of Session IDs areused, as manually configured in the StaticSession ID Persistency Table. Both Directions means WSD inspectsboth client requests and servers replies inorder to learn about persistencyidentifiers.Default value is Server Reply.Ignore Server ReplyThe possible values are: Never to ignore the server reply, meaningWSD looks in it even if WSD alreadyfound a Session ID for this session. Insuch case WSD updates the Session IDPersistency table according to theinformation in the servers reply. When ID is in Request improves WSDperformance when the Learning Directionparameter is set to Server Reply or toBoth Directions. When WSD alreadyfound a Session ID in clients request,WSD does not further inspect the serverreply. When a Session ID already exists inthe clients request, and it can beguaranteed that the server does notchange that Session ID, you can set thisfield to When ID is in Request.Tip: Use this option when Static Session IDsare used.Default value is Never.静态会话ID保持 你能在有或没有静态会话保持许可的情况下使用静态会话保持。 当没有静态会话保持许可的情况下： 静态会话ID保持允许WSD发送带有指定会话ID的流量到指定的服务器。当WSD收到一个到采用会话保持的FARM的会话，WSD检查会话ID保持表中设置的值。你能配置什么会话ID内容选择哪个服务器。 当具有静态会话保持许可时： WSD检查客户请求中的会话ID，基于原先定义的静态会话ID选择服务器。如果会话ID和值匹配了FARM中的设置，并且匹配了服务器的设置WSD发送一个HTTP重定向到客户端，利用原来客户请求中的主机名，增加了表示服务器的特别的字符。比如，当一个用户访问/index.htm，他可能被重定向到/rwABCDEFGHIJ/index.htm。当用户发送这个请求到WSD，WSD去掉这个字符串，转发请求到指定的服务器。 Q1 Learning Direction only client request, no server reply and both?Q2 What the layer 7 persistence means, theres 3 parameters?Q3 what the lookup mode difference about indicator, header and regExp?Generic Session ID version 8.20WSD version 8.20 enhances the Client Server persistency, by allowing searching for anypersistency identifier within the packet in a text format or in a binary format. WSD 8.20 allowssearching for any session ID using two mechanisms:Text Match Session ID Persistency: using the Text Match Session ID Persistency mechanism,WSD searches within the packet for text string. The search can be for any persistency identifier,anywhere in the packet, starting from the IP data, TCP data or UDP Data.Pattern Match Session ID Persistency: using the Pattern Match Session ID Persistencymechanism, WSD searches within the packet for binary patterns. Binary session ID matching isdone by using pattern matching. Administrators configure the offset at which the pattern beginsand a mask to apply to the pattern before checking whether it is found in the session ID table. Thepattern length is determined by the length of the pattern mask. The session ID itself may beconfigured manually via the static mechanism, or learned dynamically according to the serverselection that was performed on session IDs that did not already exist in the session ID table.An additional option is introduced to the session ID mechanism: an option to include the source IPin the persistency decision. When this mode is disabled, finding the session ID in the table is notenough for a persistency decision the source IP must also match. In case that the source IPdoes not match, WSD acts according to the farm session mode. The “Ignore Source IP” flagenable or disable this option. Default is “Enabled”.Session ID Load Balancing version 7.52WSD version 6.10 introduced support for cookie-based persistency now known as Session ID.Originally, this feature only allowed use of fixed and pre-defined cookie keys and values for eachserver. WSD now also supports dynamic session ID set by the servers. The user defines a fixedkey for the farm, then WSD tracks the use of different session ID values, or session IDs, bydifferent servers.When a client request arrives at the WSD without a session ID, WSD selects a server according tothe regular algorithms. The server will generate a dynamic session ID and send it to this client.WSD detects the session ID and remembers that the specific session ID was sent from thatspecific server. This information is kept in WSDs memory for a configurable period of time(Inactivity Timeout). During this period, whenever a client connects with the session ID (the clientsIP address may change), WSD will send that client to the same server that generated the ID. Asession ID is defined by its key name or key name prefix, and each ID value is attached to aspecific server. The feature searches the HTTP Header that appears in the request packet, so thatthe session ID can be found either as part of the URL or in an HTTP Header field. WSD alsosupports Multi Packet HTTP Header when using Dynamic session ID.Session ID Persistency According to HTTP Header version 8.03WSD can maintain persistence according to Session ID that appears in HTTP Header.Regular Expression for Session ID Persistency version 8.04WSD enables now to maintain server persistency according to any information that