多个tomcat配置 cluster 使用组播方式共享session，会出现session丢失：报错

最近成功使用了 Nginx + 2 个tomcat7 在一台Linux机器上实现了负载均衡。

tomcat之间通过配置cluster + web.xml 配置 <distributable /> 实现 session复制功能，但是当在web系统中点击url访问功能，会时不时出现session丢失，要求重新登录。

通过chrome或firebug看拦截每个URL时的头部 cookie，可以看到 JSESSIONID = xxxxx.jvm1 和 JSESSIONID = xxxxx.jvm2 进行切换，这说明了 nginx 负载均衡有效，将http请求分发给2个tomcat进行处理，但是当访问了几次http（或 jvm1, jvm2切换几次）后，就出现了 session 丢失，JSESSIONID 值变了，不知道为什么了？

下面的2个tomcat的 cluster 配置：

tomcat:8080

<Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"
                 channelSendOptions="8">

          <Manager className="org.apache.catalina.ha.session.DeltaManager"
                   expireSessionsOnShutdown="false"
                   notifyListenersOnReplication="true"/>

          <Channel className="org.apache.catalina.tribes.group.GroupChannel">
            <Membership className="org.apache.catalina.tribes.membership.McastService"
                        address="228.0.0.4"
                        port="45564"
                        frequency="500"
                        dropTime="3000"/>
            <Receiver className="org.apache.catalina.tribes.transport.nio.NioReceiver"
                      address="10.0.125.15"
                      port="4001"
                      autoBind="100"
                      selectorTimeout="5000"
                      maxThreads="6"/>

            <Sender className="org.apache.catalina.tribes.transport.ReplicationTransmitter">
              <Transport className="org.apache.catalina.tribes.transport.nio.PooledParallelSender"/>
            </Sender>
            <Interceptor className="org.apache.catalina.tribes.group.interceptors.TcpFailureDetector"/>
            <Interceptor className="org.apache.catalina.tribes.group.interceptors.MessageDispatch15Interceptor"/>
          </Channel>

          <Valve className="org.apache.catalina.ha.tcp.ReplicationValve"
                 filter=""/>
          <Valve className="org.apache.catalina.ha.session.JvmRouteBinderValve"/>

          <Deployer className="org.apache.catalina.ha.deploy.FarmWarDeployer"
                    tempDir="/tmp/war-temp/"
                    deployDir="/tmp/war-deploy/"
                    watchDir="/tmp/war-listen/"
                    watchEnabled="false"/>

          <ClusterListener className="org.apache.catalina.ha.session.JvmRouteSessionIDBinderListener"/>
          <ClusterListener className="org.apache.catalina.ha.session.ClusterSessionListener"/>
        </Cluster>

<Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"
                 channelSendOptions="8">

          <Manager className="org.apache.catalina.ha.session.DeltaManager"
                   expireSessionsOnShutdown="false"
                   notifyListenersOnReplication="true"/>

          <Channel className="org.apache.catalina.tribes.group.GroupChannel">
            <Membership className="org.apache.catalina.tribes.membership.McastService"
                        address="228.0.0.4"
                        port="45564"
                        frequency="500"
                        dropTime="3000"/>
            <Receiver className="org.apache.catalina.tribes.transport.nio.NioReceiver"
                      address="10.0.125.15"
                      port="4002"
                      autoBind="100"
                      selectorTimeout="5000"
                      maxThreads="6"/>

            <Sender className="org.apache.catalina.tribes.transport.ReplicationTransmitter">
              <Transport className="org.apache.catalina.tribes.transport.nio.PooledParallelSender"/>
            </Sender>
            <Interceptor className="org.apache.catalina.tribes.group.interceptors.TcpFailureDetector"/>
            <Interceptor className="org.apache.catalina.tribes.group.interceptors.MessageDispatch15Interceptor"/>
          </Channel>

          <Valve className="org.apache.catalina.ha.tcp.ReplicationValve"
                 filter=""/>
          <Valve className="org.apache.catalina.ha.session.JvmRouteBinderValve"/>

          <Deployer className="org.apache.catalina.ha.deploy.FarmWarDeployer"
                    tempDir="/tmp/war-temp/"
                    deployDir="/tmp/war-deploy/"
                    watchDir="/tmp/war-listen/"
                    watchEnabled="false"/>

          <ClusterListener className="org.apache.catalina.ha.session.JvmRouteSessionIDBinderListener"/>
          <ClusterListener className="org.apache.catalina.ha.session.ClusterSessionListener"/>
        </Cluster>

说明：

1. linux 的组播服务是正常的：route add -net 224.0.0.0 netmask 240.0.0.0 dev eth1

2. 2个tomcat之间的tcp通信也是正常的，启动2个tomcat后，会在日志中看到类似的：

Manager [localhost#/crm], requesting session state from org...Memberlmpl[tcp://{10,0,125,15}:4002] ....

3. 当我停掉一个tomcat后，令一个tomcat的日志中就会显示：

Received member disappeared:org....MemberImlp[tcp://{10,0,125,15}:4001], ...., UDP Port=-1,.. id={-3 67....}...., command={66 65 66 89......}, domain={}

以上都说明了2个tomcat之间的集群通信都是OK的，但是为什么2个tomcat之间的session共享有时正常，有时不正常呢？时不时的 session 就丢失了。

请大家帮我看看啊，我的CRM项目中使用大量的iframe，有没有可能是 iframe 造成了2个tomcat之间session共享丢失呢？