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# Apache Tomcat Configuration Reference ## The Cluster Valve object | print-friendly version
Introduction
A cluster valve is no different from any other Tomcat `Valve`. The cluster valves are interceptors in the invokation chain for HTTP requests, and the clustering implementation uses these valves to make intelligent decision around data and when data should be replicated. A cluster valve must implement the `org.apache.catalina.ha.ClusterValve` interface. This is a simple interface that extends the `org.apache.catalina.Valve` interface.
org.apache.catalina.ha.tcp.ReplicationValve
> The `ReplicationValve` will notify the cluster at the end of a HTTP request so that the cluster can make a decision whether there is data to be replicated or not.
> Attributes
> > Attribute | Description
> > --- | ---
> > `className` | Set value to `org.apache.catalina.ha.tcp.ReplicationValve`
> > `filter` | For known file extensions or urls, you can use a filter to notify the cluster that the session has not been modified during this request and the cluster doesn't have to probe the session managers for changes. If there is a filter match, the cluster assumes there has been no session change. An example filter would look like `filter=".*\.gif;.*\.js;.*\.jpg;.*\.png;.*\.htm;.*\.html;.*\.css;.*\.txt;"` The filter uses regular expressions and each filter is delimited by a semi colon. `Pattern#compile(java.lang.String)`
> > `primaryIndicator` | Boolean value, so to true, and the replication valve will insert a request attribute with the name defined by the `primaryIndicatorName` attribute. The value inserted into the request attribute is either `Boolean.TRUE` or `Boolean.FALSE`
> > `primaryIndicatorName` | Default value is `org.apache.catalina.ha.tcp.isPrimarySession` The value defined here is the name of the request attribute that contains the boolean value if the session is primary on this server or not.
> > `statistics` | Boolean value. Set to `true` if you want the valve to collect request statistics. Default value is `false`
org.apache.catalina.ha.session.JvmRouteBinderValve
> In case of a mod_jk failover, the `JvmRouteBinderValve` will replace the `jvmWorker` attribute in the session Id, to make future requests stick to this node. If you want failback capability, don't enable this valve, but if you want your failover to stick, and for mod_jk not to have to keep probing the node that went down, you use this valve.
> Attributes
> > Attribute | Description
> > --- | ---
> > `className` | `org.apache.catalina.ha.session.JvmRouteBinderValve`
> > `enabled` | Default value is `true` Runtime attribute to turn on and off turn over of the session's jvmRoute value.
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