搭建 Tomcat 集群需要解决很多的问题，其中之一就是要解决 Session 共享问题。小规模集群可以使用 Tomcat 提供的 Session Clustering 来解决。

For the impatient

Simply add

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

to your <Engine> or your <Host> element to enable clustering.

Using the above configuration will enable all-to-all session replication using the DeltaManager to replicate session deltas. By all-to-all we mean that the session gets replicated to all the other nodes in the cluster. This works great for smaller cluster but we don't recommend it for larger clusters(a lot of Tomcat nodes). Also when using the delta manager it will replicate to all nodes, even nodes that don't have the application deployed.

To get around this problem, you'll want to use the BackupManager. This manager only replicates the session data to one backup node, and only to nodes that have the application deployed. Downside of the BackupManager: not quite as battle tested as the delta manager.

Here are some of the important default values:

Multicast address is 228.0.0.4

Multicast port is 45564 (the port and the address together determine cluster membership.

The IP broadcasted is java.net.InetAddress.getLocalHost().getHostAddress() (make sure you don't broadcast 127.0.0.1, this is a common error)

The TCP port listening for replication messages is the first available server socket in range 4000-4100

Listener is configured ClusterSessionListener

Two interceptors are configured TcpFailureDetector and MessageDispatch15Interceptor

The following is the default cluster configuration:

Cluster Basics

To run session replication in your Tomcat 7.0 container, the following steps should be completed:

All your session attributes must implement java.io.Serializable

Uncomment the Cluster element in server.xml

If you have defined custom cluster valves, make sure you have the ReplicationValve defined as well under the Cluster element in server.xml

If your Tomcat instances are running on the same machine, make sure the Receiver.port attribute is unique for each instance, in most cases Tomcat is smart enough to resolve this on it's own by autodetecting available ports in the range 4000-4100

Make sure your web.xml has the <distributable/> element

If you are using mod_jk, make sure that jvmRoute attribute is set at your Engine <Engine name="Catalina" jvmRoute="node01" > and that the jvmRoute attribute value matches your worker name in workers.properties

Make sure that all nodes have the same time and sync with NTP service!

Make sure that your loadbalancer is configured for sticky session mode.

Load balancing can be achieved through many techniques, as seen in the Load Balancing chapter.

Note: Remember that your session state is tracked by a cookie, so your URL must look the same from the out side otherwise, a new session will be created.

Note: Clustering support currently requires the JDK version 1.5 or later.

The Cluster module uses the Tomcat JULI logging framework, so you can configure logging through the regular logging.properties file. To track messages, you can enable logging on the key: org.apache.catalina.tribes.MESSAGES

more see

管中窥豹

我们打开conf下的server.xml文件，找到下面这一行：

<Engine name="Catalina" defaultHost="localhost">

在这一行的下面加入如下代码：

然后再在 web 项目的 web.xml 中添加 <distributable/> 后即可完成 Tomcat Session 共享。

本文由个人 hexo 博客 迁移

date: 2017-10-11 20:53:02