The Cluster Channel object
Table of Contents
Introduction
The channel manages a set of sub components and together they create a group communication framework.
This framework is then used internally by the components that need to send messages between different Tomcat instances.
A few examples of these components would be the SimpleTcpCluster that does the messaging for the DeltaManager, or the BackupManager that uses a different replication strategy. The ReplicatedContext object does also use the channel object to communicate context attribute changes.
Nested Components
Channel/Membership:
The Membership component is responsible for auto discovering new nodes in the cluster
and also to provide for notifications for any nodes that have not responded with a heartbeat.
The default implementation uses multicast.
In the membership component you configure how your nodes, aka. members, are to be discovered and/or
divided up.
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Channel/Sender:
The Sender component manages all outbound connections and data messages that are sent
over the network from one node to another.
This component allows messages to be sent in parallel.
The default implementation uses TCP client sockets, and socket tuning for outgoing messages are
configured here.
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Channel/Sender/Transport:
The Transport component is the bottom IO layer for the sender component.
The default implementation uses non-blocking TCP client sockets.
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Channel/Receiver:
The receiver component listens for messages from other nodes.
Here you will configure the cluster thread pool, as it will dispatch incoming
messages to a thread pool for faster processing.
The default implementation uses non-blocking TCP server sockets.
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Channel/Interceptor:
The channel will send messages through an interceptor stack. Because of this, you have the ability to
customize the way messages are sent and received, and even how membership is handled.
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Attributes
Common Attributes
| Attribute | Description |
|---|---|
className |
The default value here is org.apache.catalina.tribes.group.GroupChannel and is
currently the only implementation available.
|
org.apache.catalina.tribes.group.GroupChannel Attributes
| Attribute | Description |
|---|---|
heartbeat | Flag whether the channel manages its own heartbeat. If set to true, the channel start a local thread for the heart beat. If set this flag to false, you must set SimpleTcpCluster#heartbeatBackgroundEnabled to true. default value is true. |
heartbeatSleeptime | If heartbeat == true, specifies the interval of heartbeat thread in milliseconds. The default is 5000 (5 seconds). |
optionCheck | If set to true, the GroupChannel will check the option flags that each interceptor is using. Reports an error if two interceptor share the same flag. The default is false. |
jmxEnabled | Flag whether the channel components register with JMX or not. The default value is true. |
jmxDomain |
if jmxEnabled set to true, specifies the jmx domain which
this channel should be registered. The ClusterChannel is used as the
default value.
|
jmxPrefix |
if jmxEnabled set to true, specifies the jmx prefix which
will be used with channel ObjectName.
|