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# Apache Tomcat Configuration Reference ## The Channel Interceptor object | print-friendly version
Introduction
Apache Tribes supports an interceptor architecture to intercept both messages and membership notifications. This architecture allows decoupling of logic and opens the way for some very kewl feature add ons.
Available Interceptors
`org.apache.catalina.tribes.group.interceptors.TcpFailureDetector` `org.apache.catalina.tribes.group.interceptors.ThroughputInterceptor` `org.apache.catalina.tribes.group.interceptors.MessageDispatch15Interceptor` `org.apache.catalina.tribes.group.interceptors.MessageDispatchInterceptor` `org.apache.catalina.tribes.group.interceptors.NonBlockingCoordinator` `org.apache.catalina.tribes.group.interceptors.OrderInterceptor` `org.apache.catalina.tribes.group.interceptors.StaticMembershipInterceptor` `org.apache.catalina.tribes.group.interceptors.TwoPhaseCommitInterceptor` `org.apache.catalina.tribes.group.interceptors.DomainFilterInterceptor` `org.apache.catalina.tribes.group.interceptors.FragmentationInterceptor` `org.apache.catalina.tribes.group.interceptors.GzipInterceptor`
Static Membership
> In addition to dynamic discovery, Apache Tribes also supports static membership, with membership verification. To achieve this add the `org.apache.catalina.tribes.group.interceptors.StaticMembershipInterceptor` underneath the `org.apache.catalina.tribes.group.interceptors.TcpFailureDetector` interceptor. Inside the `StaticMembershipInterceptor` you can add the static members you wish to have. The `TcpFailureDetector` will do a health check on the static members,and also monitor them for crashes so they will have the same level of notification mechanism as the members that are automatically discovered.
>          <Interceptor className="org.apache.catalina.tribes.group.interceptors.StaticMembershipInterceptor">
>            <Member className="org.apache.catalina.tribes.membership.StaticMember"
>                       port="5678"
>                       securePort="-1"
>                       host="tomcat01.mydomain.com"
>                       domain="staging-cluster"
>                       uniqueId="{0,1,2,3,4,5,6,7,8,9}"/>
>          </Interceptor>
Attributes
> Common Attributes
> > Attribute | Description
> > --- | ---
> > `className` | Required, as there is no default
> > `optionFlag` | If you want the interceptor to trigger on certain message depending on the message's option flag, you can setup the interceptors flag here. The default value is `0`, meaning this interceptor will trigger on all messages.
> org.apache.catalina.tribes.group.interceptors.MessageDispatch15Interceptor Attributes
> > Attribute | Description
> > --- | ---
> > `className` | Required, This dispatcher uses JDK 1.5 java.util.concurrent package
> > `optionFlag` | The default and hard coded value is `8 (org.apache.catalina.tribes.Channel.SEND_OPTIONS_ASYNCHRONOUS)`. The dispatcher will trigger on this value only, as it is predefined by Tribes.
> org.apache.catalina.tribes.group.interceptors.MessageDispatchInterceptor Attributes
> > Attribute | Description
> > --- | ---
> > `className` | Required, Same implementation as `MessageDispatch15Interceptor`, but with JDK 1.4 compliance.
> > `optionFlag` | The default and hard coded value is `8 (org.apache.catalina.tribes.Channel.SEND_OPTIONS_ASYNCHRONOUS)`. The dispatcher will trigger on this value only, as it is predefined by Tribes.
> > `alwaysSend` | What behavior should be executed when the dispatch queue is full. If `true` (default), then the message is is sent synchronously, if `false` an error is thrown.
> > `maxQueueSize` | Size in bytes of the dispatch queue, the default value is `1024*1024*64 (64MB)` sets the maximum queue size for the dispatch queue if the queue fills up, one can trigger the behavior, if `alwaysSend` is set to true, the mesage will be sent synchronously if the flag is false, an error is thrown
> org.apache.catalina.tribes.group.interceptors.TcpFailureDetector Attributes
> > Attribute | Description
> > --- | ---
> org.apache.catalina.tribes.group.interceptors.ThroughputInterceptor Attributes
> > Attribute | Description
> > --- | ---
> > `interval` | Defines the interval in number of messages when we are to report the throughput statistics. The report is logged to the `org.apache.juli.logging.LogFactory.getLog(ThroughputInterceptor.class)` logger under the `INFO` level. Default value is to report every `10000` messages.
> Nested element StaticMember Attributes
> > Attribute | Description
> > --- | ---
> > `className` | Only one implementation available:`org.apache.catalina.tribes.membership.StaticMember`
> > `port` | The port that this static member listens to for cluster messages
> > `securePort` | The secure port this static member listens to for encrypted cluster messages default value is `-1`, this value means the member is not listening on a secure port
> > `host` | The host (or network interface) that this static member listens for cluster messages. Three different type of values are possible: 1. IP address in the form of "216.123.1.23" 2. Hostnames like "tomcat01.mydomain.com" or "tomcat01" as long as they resolve correctly 3. byte array in string form, for example {216,123,12,3}
> > `domain` | The logical cluster domain for this this static member listens for cluster messages. Two different type of values are possible: 1. Regular string values like "staging-domain" or "tomcat-cluster" will be converted into bytes using ISO-8859-1 encoding. 2. byte array in string form, for example {216,123,12,3}
> > `uniqueId` | A universally uniqueId for this static member. The values must be 16 bytes in the following form: 1. byte array in string form, for example {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}
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